Characteristics Of Anaerobic Indigenous Arsenic-reducing Bacteriumand Its Effect On Migration And Transformation Of Arsenic And Iron

Microorganisms in groundwater systems play a significant role in the biochemical cycle of arsenic,which affect the release, migration and transformation of arsenic in the aquifer systems. In anaerobic groundwater with the coexistence of high As and Fe(II) concentrations, reductive dissolution of Fe(â…¢) oxyhydroxides have widely been accepted for mechanism of arsenic mobilization. However, few studies have explored indigenous anaerobic arsenic-resistant strains in the aquifers of the Hetao basin. Studies on characteristics and biogeochemical efffects of anaerobic indigenous arsenic-reducing bacteria in the high arsenic groundwater wouldnot only help us to better understand the roles of microorganisms in As transformation and mobility, but also enrich theories of As cycling in the environments.In this paper, a strain of anaerobic As-resistant bacterium was isolated from the aquifer sediment hosting high arsenic groundwater in the Hetao basin. By using molecular ecology technology, laboratory culture experiments, and synchrotron radiation techniques,twe have studied molecular ecology characteristics, arsenic-resistant mechanisms, and reduction characteristic and mechanisms of different form As(V) and Fe(â…¢) in the presence of indigenous anaerobic arsenic-resistant strains..Following results are obtained.(1) Sequencing of the 16 S rDNA showed that the strain(strain BH02-C for short) has a 99% similarity with Clostridium bifermentans strain E051. The arsC and arrA genes were amplified successfully by PCR technique. The length of putative arsC and arrA genes fragments were 260 bp and 390 bp, respectively. GenearrA reduces As(V) to As(â…¢) by arsenate respiratory reduction, while the reduction of As(V) by arsC is regarded as a detoxification mechanism. By these two reduction pathways, the strainwas believed to be involved in the process of As biogeochemistry.(2) As(â…¢) showed more obvious inhibitory effect on microbial growth and cellular morphology in comparison with As(V), which may be due to the much higher toxicity of As(â…¢) than that of As(V).(3)Strain BH02-Chad stronger reducing capacity of Fe(â…¢) than As(V). Resultsshowed that strain BH02-C reduced dissolved As(V) and dissolved Fe(â…¢) in the presence of organic carbon as the carbon source, and the reduction rateswere associated with the initial concentrations.The reduction rate of Fe(â…¢) was greater than that of As(V), when Fe(â…¢) or As(V) was interacted individually with bacteria.It indicated that strain BH02-Chad stronger reducing capacity of Fe(â…¢) than As(V). Strain BH02-C simultaneously reduced Fe(â…¢) and As(V), when dissolved As(V) and Fe(â…¢) coexisted in the culture.With Fe(â…¢)/As(V) molar ratio of 1.0,the Fe(â…¢) reduction rate was obviously greater.(4) Strain BH02-C was able to not only reduce dissolved Fe(â…¢) and As(V), but also reduce adsorbed and/or crystalline Fe(â…¢) and As(V). Results showed that strain BH02-C reduced Fe(â…¢) and As(V) on/ in As(V)-adsorbing goethite, scorodite and sediment, in addition todissolved Fe(â…¢) and As(V). In the presence of the strain, the amount of As released from goethite and scorodite was improved greatly, which futher promote the the mobility of As and Fe in the sediment infrom aquifer systems.