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.