Synergistic microcystin degradation by a novel bacterium isolated from shrimp pond and fulvic acids

Using the Widdel medium with extracted microcystin (MC) as the sole carbon and nitrogen sources, the MC-degrading bacteria community S₆ was enriched from the sediment of Litopenaeus vannamei pond, and a novel MC-degrading bacteria strain was isolated from S₆. According to 16S rDNA gene sequence and biochemical characteristics, the isolated strain was identified and named Nitratireductor aquimarinus D₁. Fulvic acid (FA), as a widely existing photosensitizer involved in MC photodegradation, coexists with MC-degrading bacteria in natural water. The synergistic effects of N. aquimarinus D₁ and FA on MC degradation were evaluated via comparing the degradation rate of MC induced by N. aquimarinus D₁ and FA alone and in combination under natural light conditions. Compared with the control group, the supplementation of N. aquimarinus D₁ and FA alone or in combination could significantly increase the degradation rate of MC (P<0.05). In the first 36 h, the degradation effect of FA on MC was better than that of N. aquimarinus D₁, but the degradation effect was opposite at 48 h. N. aquimarinus D₁ and FA did not show synergistic effect on MC degradation until 48 h. In the application of N. aquimarinus and FA to degrade MC in aquaculture pond, there might be a time-lag effect in the synergistic degradation.