Bacterial Community Affects Toxin Production by Gymnodinium catenatum

Abstract

The paralytic shellfish toxin (PST)-producing dinoflagellate Gymnodinium catenatum grows in association with a complex marine bacterial community that is both essential for growth and can alter culture growth dynamics. Using a bacterial community replacement approach, we examined the intracellular PST content, production rate, and profile of G. catenatum cultures grown with bacterial communities of differing complexity and composition. Clonal offspring were established from surface-sterilized resting cysts (produced by sexual crosses of strain GCDE06 and strain GCLV01) and grown with: 1) complex bacterial communities derived from each of the two parent cultures; 2) simplified bacterial communities composed of the G. catenatum-associated bacteria Marinobacter sp. strain DG879 or Alcanivorax sp. strain DG881; 3) a complex bacterial community associated with an untreated, unsterilized sexual cross of the parents. Toxin content (STX-equivalent per cell) of clonal offspring (134–197 fmol STX cell−1) was similar to the parent cultures (169–206 fmol STX cell−1), however cultures grown with single bacterial types contained less toxin (134–146 fmol STX cell−1) than offspring or parent cultures grown with more complex mixed bacterial communities (152–176 fmol STX cell−1). Specific toxin production rate (fmol STX day−1) was strongly correlated with culture growth rate. Net toxin production rate (fmol STX cell−1 day−1) did not differ among treatments, however, mean net toxin production rate of offspring was 8-fold lower than the parent cultures, suggesting that completion of the sexual lifecycle in laboratory cultures leads to reduced toxin production. The PST profiles of offspring cultures were most similar to parent GCDE06 with the exception of cultures grown with Marinobacter sp. DG879 which produced higher proportions of dcGTX2+3 and GC1+2, and lower proportions of C1+2 and C3+4. Our data demonstrate that the bacterial community can alter intracellular STX production of dinoflagellates. In G. catenatum the mechanism appears likely to be due to bacterial effects on dinoflagellate physiology rather than bacterial biotransformation of PST toxins.

Gymnodinium catenatum Graham isolated from the Portuguese coast: Toxin content and genetic characterization

“…Regarding the microbiome influence on PST content and profile, building evidence favors the hypothesis of an indirect influence of the microbiome, through mediation of dinoflagellate cell physiological processes, rather than direct bacterial PST production (Green et al, 2010;Bolch et al, 2011;Albinsson et al, 2014). Albinsson et al (2014), using cyst germination and controlled microbiome manipulation, have elegantly shown that changes in the cultureassociated microbiome influence the PST profile and net PST production in G. catenatum. In addition, these authors observed an almost 8-fold reduction in the mean net toxin production rate in offspring cultures, relative to parent cultures, suggesting the sexual process involved in cyst formation also plays an important role in toxin modulation.…”

“…The biotic and/or abiotic factors determining the differences between PSTs from cyst and plankton-derived cultures are still poorly understood and assumed to be related to the physiological process of encystment/excystment and its interplay with culture conditions (Negri et al, 2007;Hallegraeff et al, 2012;Albinsson et al, 2014). Several works have recently been published on the influence of the accompanying bacterial community (microbiome) on the physiology of Gymnodinium catenatum in culture (Green et al, 2010;Bolch et al, 2011;Albinsson et al, 2014).…”

“…Several works have recently been published on the influence of the accompanying bacterial community (microbiome) on the physiology of Gymnodinium catenatum in culture (Green et al, 2010;Bolch et al, 2011;Albinsson et al, 2014). It is now clear that G. catenatum has an obligate requirement of a marine microbiome for survival and growth (Bolch et al, 2011).…”

“…It is now clear that G. catenatum has an obligate requirement of a marine microbiome for survival and growth (Bolch et al, 2011). Regarding the microbiome influence on PST content and profile, building evidence favors the hypothesis of an indirect influence of the microbiome, through mediation of dinoflagellate cell physiological processes, rather than direct bacterial PST production (Green et al, 2010;Bolch et al, 2011;Albinsson et al, 2014). Albinsson et al (2014), using cyst germination and controlled microbiome manipulation, have elegantly shown that changes in the cultureassociated microbiome influence the PST profile and net PST production in G. catenatum.…”

Global toxicology, ecophysiology and population relationships of the chainforming PST dinoflagellate Gymnodinium catenatum

“…Culture-related factors (growth temperature, medium, and chain-length) are known to significantly alter both total STX content as well as the presence and relative (mol%) proportions of STX derivatives (Band-Schmidt et al, 2006). The composition of the associated culture bacterial community can also influence toxin content and profile, either directly by inter-conversion of toxins produced by the dinoflagellate (see Smith et al (2002) re Alexandrium minutum) or indirectly via their influence on G. catenatum growth rate and cell physiology (Albinsson et al, 2010). Comparisons of profiles obtained from the same strain by different laboratories suggest consistent differences in PST chromatogram interpretation, partly due to limited availability of verified standards for particular STX derivatives.…”