A soil-borne Mn(II)-oxidizing bacterium of Providencia sp. exploits a strategy of superoxide production coupled to hydrogen peroxide consumption to generate Mn oxides

Abstract

Bacterial non-enzymatic Mn(II) oxidation involving reactive oxygen species (ROS) (i.e. indirect oxidation), initially discovered from a marine alpha-proteobacterium, is believed to be of importance in controlling biogeochemical cycles. For soil-borne bacteria, however, evidence of indirect Mn(II) oxidation remains unclear. In this study, the indirect Mn(II) oxidation was evidenced in a soil-borne bacterium, Providencia sp. LLDRA6. First, with and without 50 mM of Mn(II) exposure for LLDRA6, 300 differentially expressed genes were found to be linked to Mn(II) exposure via transcriptome sequencing. Among them, an operon, responsible for phenylacetic acid catabolism, was sharply upregulated in transcription, drawing us a special attention since its transcriptional upregulation has recently shown to be important for withstanding ROS. Next, a uorometric probe, 2′,7′-Dichloro uorescin diacetate (DCFDA), was used to qualitatively detect ROS from cells, showing a distinct increase in uorescence intensities of ROS during Mn(II) exposure. Further, concentrations of superoxide and hydrogen peroxide from cells were detected respectively with and without Mn(II) exposure, exhibiting that when Mn(II) oxidation occurred, superoxide concentration signi cantly increased but hydrogen peroxide concentration signi cantly decreased. Particularly, superoxide produced by LLDRA6 was proven to be the oxidant for Mn(II) in the formation of Mn oxides. Finally, we predicted links between phenylacetic acid metabolism pathway and ROS during Mn(II) exposure, proposing that the excessive ROS, generated in response to Mn(II) exposure, transcriptionally activate phenylacetic acid catabolism presumably by increasing concentrations of highly reactive oxepins.

The formation of bixbyite-type Mn2O3 via pyocyanin-dependent Mn(II) oxidation of soil-derived Pseudomonas aeruginosa

“…The soil suspension was then serially diluted with sterile ddH 2 O at the same ratio, and spread onto LB agar plates supplemented with 50 mM of Mn(II) for incubation for 72 h at 35℃. A single Mn(II)-tolerant bacterial colony was selected to streak on Luria-Bertani (LB) agar plates (Chen et al, 2022) for puri cation several times, and was nally denoted as L3.…”

“…1E, the oxidation ability of strain L3 for Mn(II) was preliminarily demonstrated by LBB staining assays (Krumbein and Altmann, 1973). It can be seen that after 52 h of incubation, the cells which were cultured in LB liquid medium containing 5 or 6 mM of Mn(II), made the reagent of 0.04% LBB stain blue color, indicating the presence of Mn oxides around cells (Chen et al, 2022). By contrast, in the case of Mn(II) addition ranging from 0 to 4 mM, no blue staining evidently occurred.…”

“…Mn(II) oxidation occurs in a wide variety of bacterial species, covering α, β, γ-Proteobacteria, Firmicutes, and Actinobacteria (Tebo et al, 2005). Generally, these bacterial species may employ four different types of strategies to oxidize Mn(II) as follows: (i) direct oxidation of Mn(II) by the multicopper oxidases (MCOs), which share low homology except for their copper binding motifs (Ridge et al, 2007); (ii) direct oxidation of Mn(II) by the peroxidase cyclooxygenases, which feature animal heme peroxidase domains and hemolysin-type Ca(II) binding domains (Geszvain et al, 2016;Nakama et al, 2014); (iii) light-driven anaerobic microbial oxidation of Mn(II) (Mirna et al, 2019); (iv) indirect oxidation of Mn(II) by superoxide coupled to hydrogen peroxide consumption (Chen et al, 2022;Andeer et al, 2015).…”

Providencia manganoxydans sp. nov., a Mn(II)-oxidizing bacterium isolated from heavy metal contaminated soils in Hunan Province, China

“…Commonly, in bacterial strains equipped with the ability of Mn(II) oxidation, two protein families involve in Mn(II) oxidation, i.e. multicopper oxidases (MCOs) and peroxidase cyclooxygenases, exhibiting the homologous copper binding motifs and heme/Ca(II) binding domains, respectively [38]. After annotating the genome of LLDRA6 T by using the database of cluster of orthologous groups of proteins, two putative MCO-type proteins are found to be possibly responsible for Mn(II) oxidation, i.e.…”

“…After annotating the genome of LLDRA6 T by using the database of cluster of orthologous groups of proteins, two putative MCO-type proteins are found to be possibly responsible for Mn(II) oxidation, i.e. CotA and laccase [38]. CotA, firstly reported in Bacillus pumilus WH4, a soil-borne Mn(II)-oxidizing bacterium isolated from Fe-Mn nodules, contains four conserved copper-binding motifs, and exhibits both Mn(II)-oxidase and laccase activities [39].…”