Riboflavin content of coelomocytes in earthworm (Dendrodrilus rubidus) field populations as a molecular biomarker of soil metal pollution ISJ 9: 169-177, 2012 ISSN 1824-307X RESEARCH REPORT Searching for external sources of the riboflavin stored in earthworm eleocytes P Sulik1, M Klimek1, P Talik1, J Kruk2, AJ Morgan3, B Plytycz1 1Department of Evolutionary Immunobiology, Institute of Zoology, Jagiellonian University, Krakow, Poland 2Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland 3Cardiff School of Biosciences, Main Building, Cardiff University, Cardiff CF10 3US, Wales, UK Accepted October 1, 2012 Abstract Riboflavin (vitamin B2) is essential to maintain immune potency in animals and plants. So far is accepted that animals cannot synthesise riboflavin; they rely on plant-sourced diets and intestinal bacteria for their supplies. A unique feature of earthworm ‘hepatocyte-like’ chloragocytes and chloragocyte-derived eleocytes floating in celomic cavity is the storage of riboflavin within intracellular granules. The hypothesis was that vegetarian food-deprivation or antibiotic/antifungal treatment inhibits riboflavin accumulation in eleocytes of Eisenia andrei. The 7-week starvation inhibited worm body weight gain and worm reproduction but had insignificant effects on celomocytes, both amoebocytes and eleocytes, and eleocyte riboflavin accumulation. The 1 week or 3 week antibiotic exposure had insignificant effects on worm coelomocytes and riboflavin content. Thus, a vegetarian diet and intestinal bacteria are not the exclusive or perhaps even the main sources of eleocyte riboflavin. The role of endosymbionts in earthworm flavonoid economy warrants targeted investigation. Moreover, the possibility of horizontal transfer of riboflavin biosynthesis genes from bacteria/fungi to earthworm genomes cannot be neglected. Key Words: Eisenia andrei; food deprivation; antibiotic treatment; celomocytes; riboflavin Introduction The earthworm immune system is very efficient (Bilej et al., 2011). The immunocompetent cells (celomocytes) include amebocytes, which are classical immunocytes according to nomenclature proposed by Ottaviani (2011), and species-specific chloragogen tissue-derived free chloragocytes (eleocytes). Eleocytes (detached chloragocytes), but not amebocytes, exhibit autofluorescence (Cholewa et al., 2006) that is evidently restricted to chloragosomal vesicles (Plytycz et al., 2007). Autofluorescent self-marking, and the simplicity of non-invasive retrieval of celomocyte suspensions, make eleocytes ideal subjects for flow cytometry analysis (e.g., Cholewa et al., 2006; Plytycz and Morgan, 2011). Spectrofluorimetry has revealed that riboflavin (vitamin B2) is a prominent fluorophore contributing to eleocyte autofluorescence (Koziol et al., 2006; Cygal et al., 2007). The percentage of autofluorescent eleocytes among celomocytes and ___________________________________________________________________________ Corresponding author: Barbara Plytycz Department of Evolutionary Immunobiology, Institute of Zoology Jagiellonian University, Krakow, Poland E-mail: barbara.plytycz@uj.edu.pl the amount of riboflavin stored within eleocytes are species-specific, with some species possessing a high proportion of fluid-suspended eleocytes whilst other species have very few such eleocytes in their celom (Plytycz et al, 2006). Moreover, intrinsic edaphic variables (Plytycz and Morgan, 2011; Plytycz et al., 2011), including metal contamination (e.g., Kwadrans et al., 2008; Homa et al., 2010; Piotrowska et al., 2010; Podolak et al., 2011), can modulate eleocyte counts and riboflavin content. Lumbricid worms can expel celomocytes through their dorsal pores when irritated in natural environments (e.g., by predators) or experimentally by physicochemical stimuli such as a mild electric shock (Roch, 1979), ultrasound (Hendawi et al., 2004), or 5 % ethanol (Cooper at al., 1995). Experimental manipulations do not affect worm viability, and their immune system gradually recovers after electro-stimulation (Olchawa et al., 2003; Polanek et al., 2011). Riboflavin is not stored exclusively in eleocytes. Recent observations indicate that the attached chloragocytes of lumbricid earthworms, whether they have high or very low numbers of chloragocyte-derived eleocytes floating freely in the celomic fluid, contain significant riboflavin levels (Mazur et al., 2011). This finding 169 mailto:barbara.plytycz@uj.edu.pl Fig. 1 Schematic representation of two independent experiments designed to investigate the effects of (A) food deprivation and (B) antibiotic/antifungal treatment, respectively, on riboflavin content in the eleocytes of Eisenia andrei. In Experiment A, worms were either fed ad libitum (F treatment) or unfed (U treatment). In Experiment B, worms were exposed either to water-soaked filter paper (controls: C treatments) or to filter paper soaked with antibiotic/antifungal cocktail Cefuroxime/Fluconazole (A treatments). At the end of 7-week (Experiment A) or 1- week and 3-week (Experiment B) experimental periods, celomic fluid was expelled by electro-stimulation (X-es) and analysed. indicates that riboflavin storage plays an important role in earthworm biology. Riboflavin is synthesized by plants and many microorganisms (Bacher et al., 2000). Animals lack the riboflavin biosynthesis machinery (Fassbinder et al., 2000). Consequently, the main sources of the vitamin for earthworms are highly likely to be a plant-based detritivorous diet, intestinal microflora, and from other endosymbionts. For example, there is direct evidence for insects (Nakabachi and Ishikawa, 1999) and nematodes (Taylor et al., 2012) being provided with riboflavin by their endosymbiotic bacteria. The main aim of the present work was to find the primary source of the riboflavin accumulated in the eleocytes of the epigeic, composting, earthworm species Eisenia andrei. In the first series of experiments the worms were food-deprived (U - unfed) while in the second series they were treated with an antibiotic/antifungal cocktail (A). The working hypothesis was that eleocyte riboflavin accumulation would be decreased in celomocyte lysates by worm starvation or by reducing the gut flora, respectively. It turned out, however, that the effects of such treatments were statistically insignificant, and therefore other putative sources of riboflavin accumulated in eleocytes are discussed. Materials and Methods Earthworms Adult Eisenia andrei (Oligochaeta; Lumbricidae), field-sampled in manure and compost heap in the Sadecki Mountains (southern Poland), were kept under controlled conditions (16 ± 1 °C; 12:12 LD) in the laboratory. The worms were kept in plastic boxes with perforated lids and the moisture level was checked weekly. Groups of worms with similar individual body weights (c. 0.5 -0.6 g) were used. Experimental design (Fig. 1) Worms were subjected to celomocyte extrusion at the end of 7-week experiments on effects of starvation or after 1-week or 3-week experiments on effects of antibacterial/antifungal factors. Food deprivation (Fig. 1A) Worms with similar body weights (appr. 0.6 g) (2 boxes, 8 worms per box) were maintained on 170 fresh commercial soil (PPUH BIOVITA, Tenczynek). In the first box worms were fed (‘F’), i.e., provided ad libitum with a mixed diet comprised of dried/boiled nettle (Urtica dioica) and dandelion (Taraxacum officinale) leaves, and in the second the worms were deprived of food (i.e., unfed, ‘U’). After 7 weeks on the contrasting dietary regimes, all of the worms were weighed, their celomocyte- containing celomic fluid was extruded and analysed, and the egg capsules (cocoons) in each box were counted. The results were compared and statistically analysed. Antibacterial and antifungal treatment (Fig. 1B) Earthworms were exposed dermally to solution of antibacterial/antifungal agents since such a procedure was very efficient in studies on effects of heavy metal solutions on worm celomocytes (e.g., see Olchawa et al. 2006; Plytycz et al. 2011). Worms of similar body weight (appr. 0.5 g), 10 worms per group, were kept individually in plastic tubes on a substrate comprised entirely of daily- exchanged shredded soft filter paper (5.7 g per tubes) soaked either with water (i.e., controls: ‘C’ groups) or with an antibiotic/antifungal cocktail (‘A’ groups). The antibiotic used was Cefuroxime (Zinacef 750 inj., GLAXO), a second generation cephalosporin. The antifungal agent was Fluconazole (Diflucan 2 mg/ml inj., Pfizer), a triazole antifungal drug. These agents were diluted and combined to give concentrations of 10,000 mg kg-1 of Cefuroxime and 200 mg kg-1 of Fluconazole per in the filter paper. After one week and 3 weeks, 5 individual worms from each of the treatments (‘C’ and ‘A’, respectively) were retrieved, weighed, and their celomocytes extruded and analysed. Comparisons and statistical analysis were performed between ‘C’/‘A’ groups after 1 week, and 3 weeks, separately. Celomocyte extrusion The earthworms were stimulated for 1 min. with an electric current (4.5 V) to expel celomic fluid with suspended celomocytes through the dorsal pores. Briefly, the weighed earthworms were individually placed in Petri dishes containing 3 ml of extrusion fluid (phosphate-buffered saline, PBS, supplemented with 2.5 g/l ethylenediamine tetra- acetic acid, EDTA), and 2 ml samples of the extruded celomocyte suspensions were used for spectrofluorimetric analysis; 1 ml was fixed in 2 % formalin and used for cell counting in hemocytometer and flow cytometry. Soil-derived bacteria Soil samples were prepared according to modified procedure used previously (Wieczorek- Olchawa et al., 2003). In short, sample of air dried commercial soil (2 g) used in present experiments was shaken in 10 ml of sterile PBS on a laboratory shaker type 358 s (Elpan, Poland). After 1 h sedimentation, 1 ml of supernatant was added to 9 ml sterile bacterial broth (Biomed, Warszawa, Poland). After overnight incubation at room temperature, suspension of soil-derived bacteria was used for testing the efficiency of antibacterial/antifungal agents. Effects of Cefuroxime and Fluconazole on soil- derived bacteria Ten μl of bacteria suspensions were added to 90 μl of bacterial broth in 96-well flat-bottomed plates (Falcon), supplemented either with Cefuroxime (C) (final concentration 10,000 mg/l), or Fluconazole (F) (final concentration 200 mg/l), or Cefuroxime/Fluconazole cocktail (CF) at the same concentrations, or with an equivalent volume of PBS (controls); wells filled with broth supplemented with C, F, C/F, PBS, but without addition of soil-derived bacteria served as controls of sterility. 8 wells were used per each treatment. Plates were incubated for 20 h at room temperature. The viability of bacteria in the various treatment groups was assessed by MTT reduction test, according to modified method described by Wieczorek-Olchawa et al. (2003). The yellow MTT (3-[4,5-dimethylthiazol-2-yl]-2,5- diphenyl-tetrazolium bromide; Sigma) is reduced to blue formazan by dehydrogenases of living bacteria. In practice, 10 μl of MTT (from 5 mg/ml working solution) was added to each well and incubated for 15 min in darkness. Absorbance was measured at 570 nm on an ExpertPlus (AsysHitech GmbH, Austria) spectrometer. Flow cytometric measurement and analysis Samples of celomocytes were analysed with a FACScalibur flow cytometer (BD Biosciences). During analytical experiments, 10,000 thresholded events per worm sample were collected and analysed on the basis of their forward scatter (FS) (for cell size) and sideward scatter (SS) (cell complexity) properties. Fluorescence FL1-H (emission 530 nm; excitation 488 nm) was recorded. The resulting files were analysed using WinMDI 2.8 software (Joe Trotter, http://facs.scripps.edu), by producing dot plots of cell size versus FL1 autofluorescence. Spectrofluorimetry and analysis Spectrofluorometric measurements were performed on 2 ml riboflavin (Sigma-Aldrich) solution as a standard and on celomocyte- suspension lysates (lysed with 2 % Triton; Sigma- Aldrich) using an LS50B Perkin-Elmer Spectrofluorometer. Emission spectra of riboflavin were recorded in the 460 - 680 nm range (lambda at 370 nm), while excitation spectra were recorded in the 300 - 500 nm range (lambda at 525 nm). The spectrofluorimetric signatures of unbound riboflavin are characterised by two maxima (at 370 nm and 450 nm) in the excitation spectrum, and a maximum at 525 nm in the emission spectrum. Riboflavin standard curve was prepared using serial dilution of pure riboflavin (Sigma-Aldrich). The emission value at 525 nm in each particular celomocyte lysates was converted to amount of riboflavin (in μg) according to the standard curve, as described previously (Plytycz et al., 2006). To verify species identification, in randomly selected samples spectra of fluorophore specific for E. andrei were recorded according to the Albani et al. (2003) protocol; emission spectra were recorded in the 340 - 480 nm range (lambda at 320 nm), while excitation spectra were recorded in the 260 - 360 nm 171 http://facs.scripps.edu/ Fig. 2 Fluorescence spectra of celomocyte lysates from Eisenia andrei. Top row: spectra of fluorophore specific for E. andrei: A - emission (Mem lambda at 320 nm; peak at 370 - 380 nm); B - excitation (Mex lambda at 380 nm; peak at 314 - 320 nm). Bottom row: spectra of riboflavin: C - emission (Rem lambda at 370 nm; peak at 520 - 525 nm); D - excitation (Rex lambda at 525 nm; peaks at 370 nm and 450 nm). range (lambda at 380 nm). The spectrofluorimetric signature of E. andrei is characterised by a maximum at 314 nm in the excitation spectrum, and a maximum at 370 - 380 nm in the emission spectrum. Arbitrary units (AU) of fluorescence were recorded using Microsoft Excel v. 97. Statistical analysis The results were expressed as means ± standard errors. Differences between the means were determined with the Mann-Whitney U-test (STATGRAPHICS Plus 5.0), with the level of significance established at p < 0.05. Results Species identification (Fig. 2) Worms sampled in the Sadecki Mountains and reared in the Institute of Zoology in Krakow were identified as E. andrei on the basis of the uniformly reddish body coloration. Celomic fluid lysates of worms from the present experiments contained fluorescence spectra similar to those characteristic for the fluorophore described by Albani et al. (2003) as a presumptive diagnostic molecular marker for E. andrei (Fig. 2, top), and riboflavin-specific fluorescence spectra (Fig. 2, bottom). Cocoon production Cocoon production was inhibited in unfed worms compared with their fed counterparts (17 and 37 cocoons, respectively, produced in the 7 week treatment period, corresponding to 0.30 and 0.66 cocoons/worm/week). Cocoons were absent in worms kept for 3 weeks on filters soaked with water or antibiotic/antifungal cocktail. Effects of antibiotic/antifungal agents on soil-derived bacteria/fungi (Fig. 3) MTT reduction assay revealed the high amount of soil-derived bacteria multiplied in bacterial broth during overnight incubation. The amounts of bacteria in the control wells filled only with bacterial broth was high. Similarly high amounts of bacteria were detected in wells supplemented with antifungal agent, Fluconazole (F wells). In a sharp contrast, living bacteria were absent in broth supplemented with antibacterial Cefuroxime (C), and in the cocktail of these two agents (CF), as optical densities read at 570 nm were very low and almost identical to those of bacteria-free wells supplemented with PBS (controls of sterility), or with F, C, or CF (Fig. 3). Effects of food deprivation on coelomocytes (Fig. 4) At the end of 7-week experiments body weights were statistically significantly lower in unfed worms than in their fed ad libitum counterparts (Fig. 5). Numbers of celomocytes (CN), among them both amebocytes (AN) and eleocytes (EN), were similar in fed and unfed worms, both those counted in extruded fluid and after adjustment for reduced body mass (CN/BW, AN/BW, EN/BW). Percentages of eleocytes (E) and riboflavin content in celomocyte lysates (R) were unaffected by 7-week 172 Fig. 3 Viability of soil-derived bacteria measured by MTT reduction test after overnight in vitro incubation in the control bacterial broth or that supplemented with antifungal Fluconazole (F), or antibacterial Cefuroxime (C) or with cocktail of these two agents (C/F). Solid and empty bars - samples with and without addition of soil-derived bacteria, respectively. OD - optical density read at 570 nm. Data are presented as means ± SE; n = 8 wells per treatment. food deprivation, riboflavin amount being even higher in unfed worms after adjustment for reduced body mass (RF/BW) or eleocyte number (RF/EN), but the increase was statistically insignificant (Fig. 4). Effects of antibiotics on worm celomocytes (Fig 5) One-week dermal exposure to soft filter papers soaked with water or Cefuroxime/Fuconazole (CF) aqueous solution had no adverse effects on worm viability, while worms exposed for 3 weeks to antibiotic/antifungal agents showed impaired mobility thus experiments were terminated. Autopsy revealed presence of ingested pieces of filters in worm intestines indicating that animals were penetrated by antibacterial/antifungal cocktail both via the derma and through the digestive tract. At the end of 1-week experiments body weights were similar in worms maintained on a substrate of filter paper as the only nutritional source, and moistened either with water (C - control group) or antibiotic/fungicide Cefuroxime/Fuconazole (CF) aqueous solution (A group) (Fig. 5A). Body weights (BW) were unaffected during 1-week CF exposure, while the percentages of eleocytes (E %) tended to be increased. In the worms exposed to antibiotics/fungicides (A groups), also numbers of celomocytes, among them amebocytes and eleocytes tended to be increased. Amount of riboflavin was unaffected, both that measured in celomocyte lysates and after adjustment for body mass (RF and RF/BW, respectively), but that concerning riboflavin adjusted to eleocytes number (RF/EN) was lower in cells from worms exposed to antibacterial/antifungal cocktail than that in water exposed worms, but the difference was statistically insignificant (Fig. 5A). At the end of 3-week experiments (Fig. 5B) body weights (BW) and percentages of eleocytes (E %) among coelomocytes were similar in worms maintained on the water- and C/F-soaked filter papers as the only nutritional source (Fig. 5B). In the worms exposed to antibiotics/fungicides, numbers of amebocytes tended to be increased (CN), eleocytes (EN) were unaffected, while amount of riboflavin tended to be reduced, both total and adjusted for body mass (RF and RF/BW, respectively), with differences being statistically insignificant, but that concerning riboflavin adjusted to eleocytes number (RF/EN) was higher in the control worms that that from the A (CF-treated) group, the difference being close to significance (p = 0.06) (Fig. 5B). Discussion It is well established that riboflavin is important for the proper functioning of the innate immunity of both animals (e.g., Powers 2003; Verdrengh and Tarkowski, 2005) and plants (Dong and Beer, 2000; Asai et al., 2010; Yoshioka et al., 2011), as well as being a signalling molecule in bacterial quorum sensing (Rajamani et al., 2008; Atkinson and Williams, 2009). In earthworms riboflavin acts as a chemoattractant for celomocytes what may facilitate the targeted recruitment of immune-competent celomocytes to the site of pathogen invasion (Mazur et al., 2011). Therefore, accumulation of riboflavin in chloragosomes of chlogagocytes and chloragocyte- derived eleocytes is probably of adaptive value for earthworm species, and eleocyte riboflavin stores are mobilized mainly in a case of pathogen invasion to support immune functions (Plytycz and Morgan, 2011). 173 Fig. 4 Effects of 7-week food deprivation on adult E. andrei. Worm groups fed ad libitum on nettle and dandelion leaves were designated ‘F’ (open bars), and unfed groups were designated ‘U’ (solid bars). Body weights (BW), percentages of eleocytes (E, %), celomocyte numbers (NC), among them amoebocyte numbers (AN) and eleocyte numbers (EN), and body weight-adjusted (CN/BW; AN/BW; EN/BW); total riboflavin content (RF) in extruded celomocytes, body weight-adjusted riboflavin content (RF/BW), and riboflavin content adjusted to extruded eleocyte numbers (RF/EN). Data are presented as means ± SE; n = 8 worms per group. Lack of statistically significant differences according to Mann-Whitney U-test between F and U treatments (p > 0.05). Our working hypothesis was that riboflavin stores in eleocytes are exhausted in food-deprived worms and especially in those fed only on filter papers and exposed dermally/orally to solution of antibacterial and antifungal agents. Contrary to our expectations, these experimental manipulations had no or little effects on riboflavin status in eleocytes of E. andrei. In the first part of the present study we revealed that the riboflavin contents in eleocyte-rich celomocyte lysates were very similar in E. andrei fed ad libitum on nettle and dandelion leaves and in worms deprived of plant-derived food. Dietary restriction over a period of a few weeks has previously (Piotrowska et al., 2010; Polanek et al., 2011) been observed to have a little or no effect on the riboflavin status of circulating immune- competent cells in other earthworm species. Consequently, we excluded such a possibility that the main sources of the vitamin for earthworms is a plant-based detritivorous diet. These observations may be interpreted in a number of ways. First, it is feasible that if riboflavin is not consumed to counteract a pathogen challenge during a given period, then the vitamin budget could be maintained by recycling directly or indirectly from senescent eleocytes to newly formed eleocytes. Second, earthworms may possess enough riboflavin stored internally elsewhere, for example in the chloragogenous tissue, to maintain optimal levels in 174 Fig. 5 Effects of 1 week (Fig. 5A) or 3-weeks (Fig. 5B) antibacterial/antifungal treatments on adult E. andrei. Worms were kept on filter paper soaked either with water (control, C, open bars) or with a cocktail of antibiotic/antifungal agents (A, solid bars). Body weights (BW), percentages of eleocytes (E, %), celomocyte numbers (NC), among them amebocyte numbers (AN) and eleocyte numbers (EN), and body weight-adjusted (CN/BW; AN/BW; EN/BW); total riboflavin content (RF) in extruded celomocytes, body weight-adjusted riboflavin content (RF/BW), and riboflavin content adjusted to extruded eleocyte numbers (RF/EN). Data are presented as means ± SE; n = 5 worms per group. Lack of statistically significant differences according to Mann-Whitney U-test between C and A treatments (p > 0.05). the eleocytes stores over the time period. Third, during a period of dietary restriction riboflavin may be replenished from endosymbiont source or sources, possibly driven by upregulation through metabolic feedback. It is not possible to infer from present knowledge which of these possibilities is the most likely. Measuring systemic riboflavin-binding protein, and the immuno-localisation of its membrane-bound counterpart (Foraker et al., 2003), would be helpful in this regard. In order to check if the main source of earthworm riboflavin is intestinal microflora the second part of experiments was performed. In an attempt to reduce if not eliminate the gut flora (Thakuria et al., 2008) earthworms were maintained for a period of several weeks on a filter paper substrate spiked with water (control) or a cocktail of antibiotic and antifungal agents. Post mortem revealed that worm intestines were filled with papers, what strongly supports that Cefuroxime/Fluconazole cocktail, which successfully killed soil bacteria, might eliminate the worm gut flora. Contrary to our expectations, the riboflavin accumulation within the eleocytes was only slightly reduced in the antibiotic-exposed worms fed only with antibiotic-soaked filter paper. It is worth to notice that such dermal exposure to filter papers soaked with metal chlorides was very efficient in studies on effects of heavy metals on coelomocytes of several earthworm species, putatively by disruption of balance between coelom-invading pathogens and worm immune system (e.g., Wieczorek-Olchawa at al., 2003; Olchawa et al., 2006; Plytycz et al., 2011). It is not known whether the antibiotic is trafficked through the earthworm body and has a negative impact on endosymbionts such as Verminephrobacter (e.g., Lund et al., 2010a, b). However, investigations on insects provide concrete evidence that bacterial endosymbionts do synthesise and supply riboflavin to their hosts (Nakabachi and Ishikawa, 1999). More recently, studies have shown that the depleted genomes of the bacterial endosymbionts of certain insect species have retained ancestral genes encoding essential amino acids and components of the riboflavin-synthesis pathway (Moran et al., 2003). In an exquisite example of co-evolution, it has been 175 observed that different endosymbiont species within a given insect host species retain complimentary components of common and essential metabolic pathways (McCutcheon et al., 2009). It is not implausible that endosymbionts play similar nutritive roles in earthworms, but there is no direct evidence for the phenomenon. The fact that Verminephrobacter eiseniae is vertically inherited via the cocoons of Eisenia fetida (Davidson et al., 2008) does, however, raise the intriguing possibility that the riboflavin requirements of the developing embryo are supplied directly by this or other endosymbiont species within the egg capsule. Another possible mechanism for keeping a relatively constant riboflavin content in earthworm celomocytes would be the ‘insertion’ of riboflavin biosynthesis genes into the earthworm genome by horizontal DNA transfer from microbes. This is not as inplausible as it may appear because such lateral transfer of fungal carotenoid genes into arthropods is well documented phenomenon (Moran and Jarvik, 2010; Altincicek et al., 2012). Given the ubiquity of riboflavin in earthworms, and the immunological benefits provided by the vitamin, it is important to seek the presence of genes regulating riboflavin biosynthesis in lumbricid earthworms. Acknowledgements This work was supported by K/ZDS/001955 from the Jagiellonian University. References Albani JR, Demuynck S, Grumiaux F, Lepreˆtre A. Fluorescence fingerprints of Eisenia fetida and Eisenia andrei. Photoch. Photobiol. 78: 599- 602, 2003. Altincicek B, Kovacs JL, Gerardo NM. Horizontally transferred fungal carotenoid genes in the two- spotted spired mite Tetranychus urticae. Biol. Lett. 8: 253-257, 2012. Asai S, Mase K, Yoshioka H. A key enzyme for flavin synthesis is required for nitric oxide and reactive oxygen species production in disease resistance. Plant J. 62: 911-924, 2010. Atkinson S, Williams P. Quorum sensing and social networking in the microbial world. J. R. Soc. Interface 6: 959-978, 2009. Bacher A, Eberhardt S, Fischer M, Kis K, Richter G. Biosynthesis of vitamin B2 (riboflavin). Annu. Rev. Nutr. 20: 153-167, 2000. Bilej M, Prochazkova P, Silverowa M, Jaskova R. Earthworm immunity. Adv. Exp. Med. Biol. 708: 66-79, 2011. Cooper EL, Cossarizza A, Suzuki MM, Salvioli S, Capri M, Quaglino D, et al. Autogenic but not allogenic earthworm effector coelomocytes kill the mammalian tumor target K562. Cell Immunol. 166: 113-122, 1995. Cholewa J, Feeney GP, O’Reilly M, Stürzenbaum SR, Morgan AJ, Plytycz B. Autofluorescence in eleocytes of some earthworm species. Fol. Histochem. Cytobiol. 44: 65-71, 2006. Cygal M, Lis U, Kruk J, Plytycz B. Coelomocytes and fluorophores of the earthworm Dendrobaena veneta raised at different ambient temperatures. Acta Biol. Crac. Ser. Zool. 49: 5- 11, 2007. Davidson SK, Powell RJ, Stahl DA. Transmission of a bacterial consortium in Eisenia fetida egg capsules. Environ. Microbiol. 12: 2277-2288, 2008. Dong H, Beer SV. Riboflavin induces disease resistance in plants activating a novel signal transduction pathway. Phytopathology 90: 801- 811, 2000. Fassbinder F, Kist M, Bereswill S. Structural and functional analysis of the riboflavin synthesis genes encoding GTP cyclohydrolase II (ribA), DHBP synthase (ribD), riboflavin synthase (ribC), and riboflavin deaminase/reductase (ribD) from Heliobacter pylori strain P1. FEMS Microbiol. Lett. 191: 191-197, 2000. Foraker AB, Khantwal CM, Swaan PW. Current perspectives on the cellular uptake and trafficking of riboflavin. Adv. Drug Del. Rev. 55: 1467-1483, 2003. Hendawi M, Sauve S, Ashour M, Brousseau P, Fournier M. A new ultrasound protocol for extrusion of coelomocyte cells from the earthworm Eisenia fetida. Ecotoxicol. Environ. Saf. 59: 17-22, 2004. Homa J, Klimek M, Kruk J, Cocquerelle C, Vandenbulcke F, Plytycz B. Metal-specific effects on metallothionein gene induction and riboflavin content in coelomocytes of Allolobophora chlorotica. Ecotox. Environ. Saf. 73: 1937-1943, 2010. Koziol B, Markowicz M, Kruk J, Plytycz B. Riboflavin as a source of autofluorescence in Eisenia fetida coelomocytes. Photoch. Photobiol. 82: 570-573, 2006. Kwadrans A, Litwa J, Wołoszczakiewicz S, Księżarczyk E, Klimek M, Duchnowski M, et al. Changes in coelomocytes of the earthworm, Dendrobaena veneta, exposed to cadmium, copper, lead or nickel-contaminated soil. Acta Biol. Crac. Ser. Zool. 49: 57-62, 2008. Lund MB, Davidson SK, Holmstrup M, James S, Kjeldsen KU, Stahl DA, et al. Diversity and host specificity of the Vermnephrobacter-earthworm symbiosis. Environ. Microbiol. 12: 2142-2151, 2010a. Lund MB, Holmstrup M, Lomstein BA, Damgaard C, Schramm A. Beneficial effect of Verminephrobacter nephridial symbionts on the fitness of the earthworm Aporrectodea tuberculata. Appl. Environ. Microbiol. 76: 4738- 43, 2010b. Mazur AI, Klimek M, Morgan AJ, Plytycz B. Riboflavin storage in earthworm chloragocytes and chloragocyte-derived eleocytes and its putative role as chemoattractant for immunocompetent cells. Pedobiologia 54S: S37-S42, 2011. McCutcheon JP, McDonald BR, Moran NA. Convergent evolution of metabolic roles in bacterial co-symbionts of insects. PNAS 106: 15394-15399, 2009. Moran NA, Plague GR, Sandström JP, Wilcox JL. A genomic perspective of nutrient provisioning by bacterial symbionts of insects. Proc. Natl. Acad. Sci. (Suppl. 2) 100: 14543-14548, 2003. Moran NA, Jarvik T.Lateral transfer of genes from fungi underlies carotenoid production in aphids. Science 328: 624-627, 2010. 176 http://www.ncbi.nlm.nih.gov/pubmed/20511426 http://www.ncbi.nlm.nih.gov/pubmed/20511426 http://www.ncbi.nlm.nih.gov/pubmed/20511426 http://www.ncbi.nlm.nih.gov/pubmed/20511426 Nakabachi A, Ishikawa H. Provision of riboflavin to the host aphid, Acyrthosiphon pisum, by endosymbiotic bacteria, Buchnera. J. Insect Physiol. 45: 1-6, 1999. Olchawa E, Czerny B, Plytycz B. Wpływ temperatury i bakterii glebowych na odbudowę układu odpornościowego i reprodukcje dżdżownic (Effects of temperature and soil bacteria on restoration of the immune system and reproduction of earthworms). Acta Agrophysica 1: 705-710 (In Polish), 2003. Olchawa E, Bzowska M, Sturzenbaum SR, Morgan AJ, Plytycz B. Heavy metals effect the coelomocyte-bacteria balance in earthworms: Environmental interactions between abiotic and biotic stressors. Environ. Pollut. 142: 373-381, 2006. Ottaviani E. Immunocyte: the invertebrate counterpart of the vertebrate macrophage. Inv. Surv. J. 8: 1-4, 2011. Piotrowska E, Podolak A, Klimek M, Klimek BA, Kruk J, Plytycz B. Effects of metalliferous soil on coelomocytes from ecophysiologically contrasting lumbricid species. Acta Biol. Crac. Ser. Zool. 52: 5-17, 2010. Plytycz B, Homa J, Koziol B, Rozanowska M, Morgan AJ. Riboflavin content in autofluorescent earthworm coelomocytes is species-specific. Folia Histochem. Cytobiol. 44: 275-280, 2006. Plytycz B, Klimek M, Homa J, Tylko G, Kolaczkowska E. Flow cytometric measurement of neutral red accumulation in earthworm coelomocytes: Novel assay for studies on heavy metal exposure. Eur. J. Soil Biol. 43, 116-120, 2007. Plytycz B, Klimek M, Homa J, Kruk J, Morgan AJ. Species-specific sensitivity of earthworm coelomocytes to dermal metal (Cd, Cu, Ni, Pb, Zn) exposures: Methodological approach. Pedobiologia 54S: S203-S210, 2011a. Plytycz B, Klimek M, Klimek BA, Szymanski W, Kruk J, Morgan AJ. Riboflavin content in the coelomocytes of contrasting earthworm species is differentially affected by edaphic variables including organic matter and metal content. Pedobiologia 54S: S43-S48, 2011b. Plytycz B, Morgan AJ. Riboflavin storage in earthworm chloragocytes/eleocytes in an eco- immunology perspective. Inv. Surv. J. 8: 199- 201, 2011. Podolak A, Piotrowska E, Klimek M, Klimek BA, Kruk J, Plytycz B. Effects of nickel, zinc, and lead-contaminated soil on burrowing rate and coelomocytes of the earthworm, Allolobophora chlorotica. Folia Biologica (Kraków), 59: 91-97, 2011. Polanek K, Wroblewska M, Klimek M, Kruk J, Plytycz B. Restoration of the coelomocyte system in the fed and food-deprived earthworms Allolobophora chlorotica and Dendrobaena veneta. Acta Biol. Cracov. Ser. Zool. 53: 5-11, 2011. Powers HJ. Riboflavin (vitamin B-2) and health. Am. J. Clin. Nutr. 77: 1352-1360, 2003. Rajamani S, Bauer WD, Robinson JB, Farrow 3rd JM, Pesci EC, Teplitski M, et al. The vitamin riboflavin and its derivative lumichrome activate the LasR bacterial quorum-sensing receptor. Mol. Plant Microbe Interact. 21: 1184-1192, 2008. Roch P. Protein analysis of earthworm coelomic fluid: I. Polymorphic system of natural hemolysin of Eisenia fetida andrei. Dev. Comp. Immunol. 3: 599-608, 1979. Segerstrom SC. Stress, energy, and immunity: an ecological view. Curr. Dir. Psychol.Sci. 16:.326- 330, 2007. Taylor M, Mediannikov O, Raoult D, Greub G. Endosymbiotic bacteria associated with nematodes, ticks nd amoebae. FEMS Immunol. Med. Microbiol. 64: 21-31, 2012. Thakuria D, Schmidt O, Liliensiek AK, Egan D, Doohan FM. Field preservation and DNA extraction methods for intestinal microbial diversity analysis in earthworms. J. Microbiol. Methods 76: 226-233, 2008. Verdrengh M, Tarkowski A. Riboflavin in innate and acquired immune responses. Inflamm. Res. 54, 390-393, 2005. Wieczorek-Olchawa E, Niklinska M, Miedzobrodzki J, Plytycz B. Effects of temperature and soil pollution on the presence of bacteria, coelomocytes and brown bodies in coelomic fluid of Dendrobaena veneta. Pedobiologia 47: 702-709, 2003. Yoshioka H, Mase K, Yoshioka M, Kobayashi M, Asai S. Regulatory mechanisms of nitric oxide and reactive oxygen species generation and their role in plant immunity. Nitric Oxide 25: 216-221, 2011. 177 http://www.ncbi.nlm.nih.gov/pubmed/18645630 http://www.ncbi.nlm.nih.gov/pubmed/19038293 http://www.ncbi.nlm.nih.gov/pubmed/19038293 http://www.ncbi.nlm.nih.gov/pubmed/19038293 1Department of Evolutionary Immunobiology, Institute of Zoology, Jagiellonian University, Krakow, Poland This work was supported by K/ZDS/001955 from the Jagiellonian University.