ARS | Publication request: Characterizing the role of a bacterial consortium in the reproduction of the model symbiotic squid, Euprymna scolopes

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: October 26, 2012
Publication Date: October 26, 2012
Citation: Kerwin, A.J., Frasca, S., O'Donnell, K., Sutton, D.A., Nyholm, S.V. 2012. Characterizing the role of a bacterial consortium in the reproduction of the model symbiotic squid, Euprymna scolopes. American Society for Microbiology.

Technical Abstract: The Euprymna scolopes – Vibrio fischeri association has been a model for the elucidation of numerous beneficial host/microbe interactions, including quorum sensing, host immune response to beneficial and environmental microbes, and symbiont specificity. Recently, the bacterial consortium contained within the accessory nidamental gland (ANG), part of the reproductive system of female E. scolopes, has come under scrutiny. Ribosomal fluorescence in situ hybridization of freshly laid eggs showed that the jelly coat contains populations of bacteria similar to that found in the ANG, suggesting that bacteria are deposited directly into the eggs. The role of these bacteria in the reproduction of this and other cephalopod species is unknown but has been hypothesized to be involved with providing protection for the developing embryos, possibly by the prevention of biofilm fouling. To begin to explore the function of the ANG bacterial consortium, we conducted a series of experiments whereby development of egg clutches (with and without antibiotic treatment) was monitored over a four-week period. Treatment of squid egg clutches with chloramphenicol led to the development of a thick biofilm and the death of the embryos (0% viability; n = 7 clutches). Clutches treated with ethanol (the chloramphenicol vehicle; n = 5 clutches) or those left untreated (n = 7 clutches) had no observed biofilms and developed and hatched at normal levels (>62% viability). Numerous fungal hyphae were observed in DAPI-stained biofilms by fluorescence microscopy. The fungal biofilm generally appeared 11-19 days after the antibiotic-treated clutches were deposited. A fungal culture was isolated on inhibitory mold agar with gentamicin. Morphological characterization and preliminary multi-locus sequence typing using four genes (TEF1-a, RPB2, ITS rDNA, and the 5’ end of LSU rDNA) suggest that this isolate is a haplotype of an unnamed phylogenetically distinct species (designated FSSC 2), located within the Fusarium solani species complex (FSSC), a species that includes pathogens of marine animals. Taken together, these data suggest ANG bacteria may protect developing squid embryos from fungal biofilms, similar to what has been described for bacterial egg protection of other marine invertebrates. Current work is focused on testing whether cultured ANG bacterial strains inhibit fungal and other microbial biofilms, characterizing bacterial gene expression in the eggs and ANG, and monitoring the bacterial egg population during embryogenesis.