Anaerobic enrichment and succession of microcystins (MCs)-degrading bacteria communities from shrimp pond sediment and shrimp intestine
Under anaerobic conditions, MCs-degrading bacteria from shrimp pond sediment and shrimp intestine were repeatedly enriched using widdel medium with MCs as the sole source of carbon and nitrogen. The succession of two bacterial communities during anaerobic enrichments were compared and anaerobic MCs-degrading bacteria strains were isolated from the final enriched bacteria communities. The results showed that with the increase of enrichment times, the alpha diversity indices of bacteria communities from pond sediment and shrimp intestine decreased significantly at first (P0.05). The composition of dominant genera changed significantly at first, and then gradually stabilized. After enrichment for 6 times, the bacteria communities from pond sediment and shrimp intestine had similar microbial diversity and essentially the same dominant genera. Principal coordinate analysis (PCoA) revealed there was significant differentiation of the original bacterial communities between pond sediment and shrimp intestine, but no significant separation of the final enriched communities. Compared with the original bacterial communities, the degradation rates of MCs by the final enriched communities from pond sediment and shrimp intestine was increased by 1.01 times and 1.42 times, respectively. Three anaerobic MCs-degrading bacteria strains were isolated from the final enriched bacteria communities and identified as Shewanella algae, Serratia marcescens, and Bacillus flexu. They could all degrade MCs, but there were significant differences in their degradation rate, which could reach more than 100 times different. Our results suggest common native anaerobic MCs-degrading bacteria community exists at different sites in the shrimp pond, and anaerobic biodegradation plays an important role in eliminating MCs pollution in shrimp pond.