Anaerobic Enrichment and Succession of Microcystin-Degrading Bacterial Communities from Shrimp Pond Sediment and Shrimp Intestine

Abstract

Under anaerobic conditions, microcystins (MCs)-degrading bacteria from shrimp pond sediment and the 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 enrichment was compared, and anaerobic MC-degrading bacterial strains were isolated from the final enriched bacterial communities. The results showed that, with the increase in the enrichment time, the alpha diversity indices of the bacterial communities from the pond sediment and shrimp intestine decreased significantly at first (p<0.05) and then increased gradually, but the difference was not significant (p>0.05). The composition of the dominant genera changed significantly at first and then gradually stabilized. After six instances of enrichment, the bacterial communities from the pond sediment and shrimp intestine had similar microbial diversity and essentially the same dominant genera. Principal coordinate analysis (PCoA) revealed the significant differentiation of the original bacterial communities between the 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 the pond sediment and shrimp intestine were increased by 1.01 times and 1.42 times, respectively. Three anaerobic MC-degrading bacterial strains were isolated from the final enriched bacterial communities and identified as Shewanella algae, Serratia marcescens, and Bacillus flexu. They could all degrade MCs, but there were significant differences in their degradation rates, which could differ by more than 100 times. Our results suggest that a common native anaerobic MC-degrading bacterial community exists at different sites in the shrimp pond, and anaerobic biodegradation plays an important role in eliminating MC pollution in shrimp ponds.