Reproducibility of a microbial river water community to self-organize upon perturbation with the natural chemical enantiomers, R- and S-carvone.

A river water microbial community was studied in response to perturbation with the monoterpene enantiomers R- and S-carvone. The microbial community structure and function was also evaluated after enantiomers exposure was switched. Microbial communities were evaluated by length heterogeneity PCR. The addition of R- and S-carvone enriched for a range of functionally different communities: enantiomer-selective, racemic and ones that contain both. After 5 days incubation, the R- and S-carvone treatments developed a range of dominant microbial communities, which were increasingly dissimilar from the ones in which no carvone degradation had taken place (R-values: R-carvone 0.743, S-carvone 0.5007). There was an increase in the evenness of the microbial community structure upon carvone depletion. After the cross-over, the rate of carvone utilization was significantly faster than after the first carvone addition (P=0.008) as demonstrated by concomitant carvone and oxygen depletion. The main R-degrading community (450-456 bp) appeared enantioselective and largely unable to degrade S-carvone, whereas the S-carvone-degrading community (502-508 bp) appeared to have racemic catabolic capacity. In conclusion, chemical perturbations, such as enantiomers, might generate a significant shift in the river microbial ecology that can have implications for the function of a river in both a spatial and temporal context.