Comparisons of four As(V)-respiring bacteria from contaminated aquifers: activities to respire soluble As(V) and to reductively mobilize solid As(V)

Abstract

It was shown that dissimilatory arsenate[As(V)]-respiring prokaryotes (DARPs) play important roles in driving the formation of arsenic-contaminated groundwater. However, because it is tough to isolate cultivable DARPs, the physiological and functional features of DARPs have not been fully elucidated yet; this impedes a deep understanding of the mechanisms for the dynamic fluctuations of As concentrations in contaminated groundwater. Here, four new DARPs were isolated from As-contaminated aquifers using the microbial enrichment technique, which were referred to as Bacillus sp Z01, Bacillus sp. Z02. Achromobacter sp. Z03 and Intrasporangium sp. Z04. We found that the presence of As(V) significantly inhibited the growth of Z03 and Z04, but promoted the growth of Z01 and Z02. The four strains possess significant As(V)-, NO3–- and Fe(III)-respiring activities; however, their activities and preferred electron donors differ greatly. NO3– was finally reduced to NO2– by Z01 and Z02, and to N2O and N2 by Z03 and Z04. The optimal pH value for their As(V)-respiring activity was 5 for Z01, and 4 for Z02, Z03 and Z04, whereas their optimal temperature varied between 30 and 37 °C. Microcosm assays with As-contaminated sediments and scorodite suggested that the four DARP strains had highly differential activities to reduce and mobilize solid As(V) under anaerobic conditions. Although the four DARPs have high soluble As(V)-respiring activities, their activities to mobilize solid As are negligibly low, accounting for only 0.006-0.484% of their each corresponding soluble As(V)-respiring activity. Moreover, extreme inconsistency between the size orders of their activities to respire soluble As(V) and to catalyze As reductive mobilization was observed. It is interesting to see that Z04 had high As(V)-respiring activity, but had little ability to catalyze the reductive mobilization of As and Fe. These observations suggest that As(V)-respiring activity is required, but not enough to catalyze the reductive mobilization of solid As(V). These findings provide new knowledge about the physiological and functional features of DARPs, and are helpful for a better understanding of the roles of DARPs in reductive mobilization and release of As from solid phase into groundwater.