Manganese(Mn)is an important metal in geochemical cycles.Some microorganisms can oxidize Mn(II)to Mn oxides,which can,in turn,affect the global cycles of other elements by strong sorption and oxidation effects.Microbe-microbe interactions play important roles in a number of biological processes.However,how microbial interactions affect Mn(II)oxidation still remains unknown.Here,we investigated the interactions between two bacteria(Arthrobacter sp.and Sphingopyxis sp.)in a co-culture,which exhibited Mn(II)-oxidizing activity,although neither were able to oxidize Mn(II)in isolation.We demonstrated that theMn(II)-oxidizing activity in co-culture was most likely induced via contact-dependent interactions.The expressed Mn(II)-oxidizing protein in the co-culture was purified and identified as abilirubin oxidase belonging to strain Arthrobacter.Full sequencing of the bilirubin oxidase-encoding gene(box)was performed.The Mn(II)-oxidizing protein and the transcripts of box were detected in the co-culture,but not in either of the isolated cultures.This indicated that box was silent in Arthrobacter monoculture,and was activated by Sphingopyxis in the co-culture.Further,transcriptomic analysis by RNA-Seq,extracellular superoxide detection,and cell density quantification by flow cytometry indicate induction of box gene expression in Arthrobacter was associated with stress imposed by Sphingopyxis.Our findings suggest the potential roles of microbial physiological responses to stress imposed by other microbes in Mn(II)oxidation.