Study On Mn(?) Indirect Oxidation Mode By A Soil-borne Bacterium—Providencia Sp.LLDRA6

As one of the strongest sorbents and oxidants in the environment,manganese oxide minerals,mainly formed by bacterial Mn(?)oxidation,are of importance in controlling countless biogeochemical cycles.Commonly,most bacterially driven Mn(?)oxidation is proposed to be linked to direct enzymatic oxidation.Recently,discovery of non-enzymatic Mn(?)oxidation by a marine alpha-proteobacterium brings us a new insight for indirect oxidation involving reactive oxygen species(ROS).For soil-borne bacteria,however,knowledge of indirect Mn(?)oxidation is as yet unknown.In this work,we studied the molecular mechanism and Mn(?)oxidation mode of a soil-borne bacterium from Providencia sp..Firstly,according to these theories,Leucoberbelin blue I(LBB)and high-valent manganese ions can generate dark blue substance,and the product that Mn(?)bind specifically with Sodium pyrophosphate(PP)has an obvious absorption peak at 258 nm,Mn(?)was oxidized by Providencia sp.LLDRA6 was confirmed.The quantitative detection of Bio Mn O_x showed that the strain had good oxidizing equivalents of Mn at50 m M Mn(?).It was also found that the effect of PP captures Mn(?)was best when the strain was cultured for 4 h first,then added PP to react for 8 h.Then,genome and transcriptome sequencing was used to analyze genes and their annotated proteins responsible for Mn(?)oxidation.Although two proteins,which contain copper binding motifs that are usually characteristics of enzymes catalyzing for Mn(?)oxidation,were found in this bacterium,no clear clues suggested that they did play a major role in Mn(?)oxidation.However,an operon responsible for phenylacetic acid(PAA)catabolism,which seemingly has nothing to do with enzymatic Mn(?)oxidation but is considered to be important for withstanding ROS,was found to be the most up-regulated in transcription during Mn(?)oxidation.Finally,according to this clue,fluorescent assays for ROS variation in this bacterium were performed during Mn(?)oxidation.It was found that the content of intracellular ROS increased under Mn(?)stress.Combining the production of superoxide and the consumption of hydrogen peroxide,the Providencia sp.LLDRA6 utilizes the indirect oxidation mode to oxidize Mn(?)is proved.In addition,it is hypothesized that the excessive ROS,generated in response to oxidative stress caused by Mn(?)in this Mn(?)-oxidizing bacterium,which leads to the increasing concentration of intracellular oxepins(phenylacetic acid metabolite),therefore the significant up-regulation of PAA metabolic pathway at the transcription level.