The effects of heavy metals on the community structure of symbiotic gut microbes in Fundulus heteroclitus

Background/Question/Methods

The magnitude of the role symbiotic microbial communities serve in respect to their host organism’s health has only recently been realized.  Still, little is known about how environmental contaminants such as heavy metals may alter these microbial assemblages. In this study, we investigate how heavy metal contamination may alter gut microbiota composition in Fundulus heteroclitus.  Fish were sourced from two sites; Callahan Mine (CM, n=6), an EPA Superfund site in Brooksville, ME, and a reference site (NEC, n=6) on Mount Desert Island, ME. A third group of fish from Callahan Mine (CMR, n=6) and maintained in reference-like conditions for one year to identify possible plasticity within the microbiota. Microbial DNA was sequenced by 454 pyrosequencing and tail clippings were taken for genotyping. 

Results/Conclusions

Overall, Lactococcus was the most abundant genus, contributing to 12.70 + 1.56% (CM), 23.13 + 7.36% (CMR), and 32.56 + 5.77% (NEC) of the resident microbiota (ANOVA, df=2, F=3.595, p=0.055). Shewanella was more abundant in CM fish (9.94 + 2.01%), made up 6.29 + 2.30% of CMR, and 2.85 + 1.77% of NEC intestinal mucosal bacteria (ANOVA, df=2, F=2.895, p=0.089). Microbiota from NEC had a higher average percent of Leuconostoc and Lactococcus present. Leuconostoc accounted for 10.62 + 1.84% of the microbiota in NEC, 3.82 + 0.52% in CM, and 7.82 + 2.55% in CMR fish (ANOVA, df=2, F=3.073, p=0.078).  CMR microbiota had intermediate abundances of Shewanella, Leuconostoc, and Lactococcus. Sex of the host fish was not found to contribute to differences in microbiota abundances. These findings suggest that the surrounding environmental conditions (i.e. metal contamination at CM) may be a factor in driving microbiota composition and structure.