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

Molecular response to the influences of Cu(II) and Fe(III) on forming biogenic manganese oxides by Pseudomonas putida MnB1

The biogeochemical cycle of biogenic manganese oxides (BioMnOx) is closely associated with the environmental behavior and fate of various pollutants. It is significantly interfered by many metals, such as Cu and Fe. However, the bacterial molecular responses are not clear. Here, the effects of Cu(II) and Fe(III) on oxidation of manganese by Pseudomonas putida MnB1 and the bacterial molecular response mechanisms have been studied. The bacterial oxidation of manganese were promoted by both Fe(III) and Cu(II) and the final manganese oxidation rate of the Cu(II) group exceeded 16 % that of the Fe(III) group. The results of transcriptome indicated that Cu(II) promoted manganese oxidation by up-regulating the expression levels of multicopper oxidase (MCO) and peroxidase(POD), and by stimulating electron transfer, while Fe(III) promoted this process by accelerating the electron transfer and nitrogen cycling, and activating POD. The protein-protein interaction (PPI) network indicated that the MCO genes (mnxG and mcoA) were directly linked to the copper homeostasis proteins (cusA, cusB, czcC and cusF). Cytochrome c was closely related to the genes related to nitrogen cycling (glnA, glnL, and putA) and electrons transfer (cycO, cycD, nuoA, nuoK, and nuoL), which also promoted manganese oxidation. This study provides a molecular level insight into the oxidation of Mn(II) by Pseudomonas putida MnB1 with Cu(II) and/or Fe(III) ions.

Alleviation of cadmium uptake in rice (Oryza sativa L.) by iron plaque on the root surface generated by Providencia manganoxydans via Fe(II) oxidation

Iron plaque is believed to be effective in reducing the accumulation of heavy metals in rice. In this work, a known soil-derived Mn(II)-oxidizing bacterium, LLDRA6, which represents the type strain of Providencia manganoxydans, was employed to investigate the feasibility of decreasing cadmium (Cd) accumulation in rice by promoting the formation of iron plaque on the root surface. Firstly, the Fe(II) oxidation ability of LLDRA6 was evaluated using various techniques including Fourier Transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, phenanthroline photometry, and FeS gel-stabilized gradient assays. Subsequently, the formation of iron plaque on the root surface by LLDRA6 was investigated under hydroponic and pot conditions. Finally, Cd concentrations were examined in rice with and without iron plaque through pot and paddy-field tests. The results showed that LLDRA6 played an efficient role in the formation of iron plaque on seedling roots under hydroponic conditions, generating 44.87 and 36.72 g kg- 1 of iron plaque on the roots of Huazhan and TP309, respectively. In pot experiments, LLDRA6 produced iron plaque exclusively in the presence of Fe(II). Otherwise, it solely generated biofilm on the root surface. Together with Fe(II), LLDRA6 effectively reduced the concentrations of Cd in Huazhan roots, straws and grains by 25%, 46% and 44%, respectively. This combination also demonstrated a significant decrease in the Cd concentrations of TP309 roots, straws and grains by 20%, 52% and 44%, respectively. The data from the Cd translocation factor indicate that obstruction of Cd translocation by iron plaque predominantly occurred during the root-to-straw stage. In paddy-field tests, the Cd concentrations of grains harvested from the combination treatment of LLDRA6 and Fe(II) exhibited a decline ranging from 40 to 53%, which fell below the maximum acceptable value for Cd in rice grains (0.2 mg kg- 1) as per the China national standard for food security (GB2762-2017). Meanwhile, the relevant phenotypic traits regarding the yield were not adversely affected. These findings have demonstrated that LLDRA6 can impede the uptake of Cd by rice in Cd-contaminated soils through the formation of iron plaque on roots, thus providing a promising safe Cd-barrier for rice production.

Abiotic transformation of atrazine in aqueous phase by biogenic bixbyite-type Mn2O3 produced by a soil-derived Mn(II)-oxidizing bacterium of Providencia sp

Recently, biogenic Mn oxides (BioMnO_x) are considered as the promising degradation agents for environmental organic contaminants. However, little information is available for the degradation of atrazine by BioMnO_x. In this work, BioMnO_x, generated by a soil-derived Mn(II)-oxidizing bacterium, Providencia sp. LLDRA6, was explored to degrade atrazine. To begin with, collective results from mineral characterization analyses demonstrated that this BioMnO_x was biogenic bixbyite-type Mn₂O₃. After that, purified biogenic Mn₂O₃ was found to exhibit a much higher removal efficiency for atrazine in aqueous phase, as compared to unpurified biogenic Mn₂O₃ and LLDRA6 biomass. During the atrazine removal by biogenic Mn₂O₃, six intermediate degradation products were discovered, comprising deethylatrazine (DEA), hydroxylatrazine (HA), deethylhydroxyatrazine (DEHA), ammeline, cyanuric acid, and 5-methylhexahydro-1,3,5-triazine-2-thione (MTT). Particularly, the intermediate, MTT, was considered as a new degradation product of atrazine, which was not described previously. Meanwhile, Mn(II) ions were released from biogenic Mn₂O₃, and on the surface of biogenic Mn₂O₃, the content of hydroxyl O species increased at the expense of that of lattice and water O species, but the fundamental crystalline structure of this Mn oxide remained unchanged. Additionally, no dissociative Mn(III) was found to involve in atrazine degradation. In summary, these results demonstrated that both the non-oxidative and oxidative reactions underlay the degradation of atrazine by biogenic Mn₂O₃.

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

A facultatively anaerobic, Gram-negative, rod-shaped bacterial strain designated as LLDRA6T, was isolated from heavy metal contaminated soils collected near a ceased smelting factory at Zhuzhou, Hunan Province, China. Strain LLDRA6T has the ability to oxidize Mn(II) and generate biogenic manganese oxides. The strain can grow in a wide range of temperature from 10–42°C and pH from 5 to 10. Comparative analysis of its complete 16S rRNA gene sequence suggests that strain LLDRA6T is highly similar to species within the genus Providencia . The complete genome of LLDRA6T is 4 342 370 bp with 40.18 mol% of G+C content and contains no plasmids. In comparison to the genomes of type strains in Providencia , LLDRA6T shows average nucleotide identity values between 76.60 and 80.89 %, and digital DNA–DNA hybridization values in a range of 21.2–24.6 %. Both multilocus sequence analysis and genomic phylogenetics indicate a new taxonomic status for LLDRA6T in Providencia . Chemotaxonomic analyses for LLDRA6T show that the predominant cellular fatty acids are C16 : 0, C14 : 0 and cyclo-C17 : 0, accounting for 32.7, 16.1 and 10.3 % of total fatty acids, respectively. The polar lipids consist of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, four unidentified aminolipids, one unidentified phospholipid and three unidentified lipids. Within the cell wall, ribose and meso-diaminopimelic acid are the characteristic constituents for saccharides and amino acids, respectively. Respiratory quinones on cell membranes are composed of menaquinone (MK) and ubiquinone (coenzyme Q), including MK-8 (100.0 %), Q-7 (13.7 %) and Q-8 (86.3 %). Moreover, the positive results from d-lyxose and d-mannitol fermentation tests indicate that LLDRA6T is totally different from all the type strains within the genus Providencia . In summary, strain LLDRA6T represents a novel species in the genus Providencia , for which the name Providencia manganoxydans sp. nov. (type strain LLDRA6T=CCTCC AB 2021154T=KCTC 92091T) is proposed.