Abstract
Previously, we found that arsenite (AsIII) oxidation could improve the generation of ATP/NADH to support the growth of Agrobacterium tumefaciens GW4. In this study, we found that aioE is induced by AsIII and located in the arsenic island near the AsIII oxidase genes aioBA and co-transcripted with the arsenic resistant genes arsR1-arsC1-arsC2-acr3-1. AioE belongs to TrkA family corresponding the electron transport function with the generation of NADH and H+. An aioE in-frame deletion strain showed a null AsIII oxidation and a reduced AsIII resistance, while a cytC mutant only reduced AsIII oxidation efficiency. With AsIII, aioE was directly related to the increase of NADH, while cytC was essential for ATP generation. In addition, cyclic voltammetry analysis showed that the redox potential (ORP) of AioBA and AioE were +0.297 mV vs. NHE and +0.255 mV vs. NHE, respectively. The ORP gradient is AioBA > AioE > CytC (+0.217 ~ +0.251 mV vs. NHE), which infers that electron may transfer from AioBA to CytC via AioE. The results indicate that AioE may act as a novel AsIII oxidation electron transporter associated with NADH generation. Since AsIII oxidation contributes AsIII detoxification, the essential of AioE for AsIII resistance is also reasonable.
Highlights
Microbial AsIII oxidation is an elaborate regulation process[11,12,13,14]
We found an oxioreductase, AioE, was obviously up-regulated with a 10.5 folds change in the presence of AsIII in A. tumefaciens GW4 (AWGV01000000)
The results indicated that aioE is essential to AsIII oxidation and enhanced bacterial growth, and that cytC participates in AsIII oxidation, but its role is less significant compared to aioE in strain GW4
Summary
Microbial AsIII oxidation is an elaborate regulation process[11,12,13,14]. The AsIII oxidase AioBA consists of two heterologous subunits, and is responsible for catalyzing bacterial AsIII oxidation[11,15]. Using comparative proteomics analysis, we found an oxidoreductase (named AioE) was obviously up-regulated in the presence of AsIII, as well as the AsIII oxidation electron transporter CytC and the large subunit www.nature.com/scientificreports/. According to BlastP analysis, AioE belongs to a TrkA superfamily and contains a NAD+ binding domain, which could incorporate one hydroxyl group to carbonyl group by concomitant generation of NADH and H+ 30,31. Such function shares similarities with the reaction converting reduced AioBA back to oxidized AioBA29,31,32. Considering its gene function and encoding protein domains, we propose that AioE may be involved in AsIII oxidation electron transport associating the generation of NADH
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