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Arsenic(As)is a well-known toxic metal.Its toxicity depends on its speciation in the environment.Generally,arsenite(As(Ⅲ))is 50-100 times more toxic than arsenate(As(Ⅴ)).Microorganisms play an important role in the As biogeochemical cycle and series of As(Ⅴ)-reducing bacteria have been isolated under anaerobic conditions for decades.However,reports of aerobic As(Ⅴ)-reducing bacteria are limited,and so far the effects of aerobic As(Ⅴ)-reducing bacteria on As behaviors is not clear.Therefore,the need for in situ monitor of As(Ⅴ)-bacteria interaction is of great importance.Surface-enhanced Raman scattering(SERS)is considered to be a promising tool for the in situ analysis of toxic metals for its sensitivity and selectivity.Our previous work indicated that phosphate modified nanoparticles can be used as a reliable SERS substrate for As speciation analysis.In situ flow cell of SERS analysis was used for real time monitoring the As biotransformation by Pantoea sp.IMH isolated in geogenic As area.The primary SERS peaks of As(Ⅲ)and As(Ⅴ)were located at720 cm-1 and 780 cm-1,respectively.While the mixture of As(Ⅴ)solution and strain IMH in logarithmic phaseflow into the cell,the time-variable SERS signals were obtained.The peak of As(Ⅲ)was increased while theAs(Ⅴ)decreased.This SERS architecture enables a highly reproducible,continuous detection of time-variable of As speciation,which is fundamental important in understanding the fate and transport of As in the environment.