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.