[Isolation and characterization of a humic-reducing bacterium Shewanella strain W3 from mangrove sediment]

A humus-reducing bacterium strain W3 was isolated from the mangrove sediment. Based on the analysis of morphology, physiobiochemical characteristics and 16S rDNA gene sequence, this strain was identified as Shewanella sp. W3. Strain W3 was able to reduce humic with lactate, formate and pyruvate as electron donor and the humic reduction rates to 1 mmol/L AQDS were 96%, 40% and 10% respectively within 48 hours. In addition, the bacteria can grow coupled with the humic reduction. Strain W3 grew to maximal density of 1.77 x 10(8) CFU/mL after complete reduction of 1 mmol/L AQDS. However, the growth of strain W3 was light increase in the control experiment in the absence of electron donor. The optimal initial pH, NaCl concentration, and temperature for strain W3 reducing humic were pH 7-9, 5-30 g/L, and 30-35 degrees C, respectively. Combined experimental results showed that the humic reduction was a biochemical process and strain W3 could conserve energy to support growth from lactate oxidation coupled to humic reduction. It is suggested that humic reduction by Shewanella bacteria may play important roles in biogeochemical circulation of elements and have potential application in the microbial bioremediation to contaminations.