Molecular identification of indigenous manganese solubilising bacterial biodiversity from manganese mining deposits

Biogenic Mn Oxide Generation and Mn(II) Removal by a Manganese Oxidizing Bacterium Bacillus sp. Strain M2

Mn(II)-oxidizing bacteria (MOB) are widely distributed in natural environments and can convert soluble Mn(II) into insoluble Mn(III) and Mn(IV). The biogenic manganese oxides (BioMnOx) produced by MOB have been considered for remediating heavy metal pollution and degrading organic pollutants in an eco-friendly manner. In this study, a manganese-oxidizing bacterium was isolated from Mn-polluted rivulet sediment and identified as Bacillus sp. strain M2 by PCR, phylogenetic tree construction, transmission electron microscopy (TEM), and physiological and biochemical indices. Strain M2 grew well under Mn(II) stress. BioMnOx with nanosized irregular geometric shapes and loose structures generated by strain M2 were found on the surface of the bacterial cells. The content of Mn in the bacteria was as high as 5.36%. Approximately 71.24% and 47.52% of Mn(II) was oxidized to Mn(III/IV) in the cell and in the deposits, respectively, within 3 d of cultivation with Mn(II). Extracellular enzymes contributed to the Mn removal and oxidation. In conclusion, Bacillus sp. strain M2 has a high potential for use in the remediation of Mn-contaminated sites.

Detection of Environmental Microfiber Pollutants through Vibrational Spectroscopic Techniques: Recent Advances of Environmental Monitoring and Future Prospects

A robust environmental monitoring system is highly essential for the instant detection of environmental microfiber pollutants for the sustainable management of the environment and human health. The extent of microfiber pollution is growing exponentially across the globe in both terrestrial and marine environments. An immediate and accurate environmental monitoring system is crucial to investigate the composition and distribution of these micropollutants. Fourier Transform Infrared Spectroscopy and Raman Spectroscopy are vibrational spectroscopic techniques that have the novel ability to detect microfibers within a minute concentration from diverse environmental samples. The major micropollutants which have been analyzed are polyethylene, polypropylene, nylon 6, polystyrene, and polyethylene terephthalate. After a detailed and critical study of the various aspects of spectroscopic analysis, the review is concluded with a comprehensive discussion of the significance of these robust methods and their application in future aspects for further preventing microfiber pollution in the marine environment. This study highlights the utilities and significance of vibrational spectroscopic detection techniques for the immediate and accurate identification of synthetic microfibers. This review also evaluated the implementation of spectroscopic methods as a precise tool for the characterization and monitoring of microfiber pollutants in the environment.

Insights Into Manganese Solubilizing Bacillus spp. for Improving Plant Growth and Manganese Uptake in Maize

Manganese (Mn) is an essential micronutrient for plant growth that is involved in the structure of photosynthetic proteins and enzymes. Mn deficiency is widespread mainly in dry, calcareous, and sandy soil, which leads to a significant decrease in crop yield. Mn-reducing bacteria promote the solubilization of Mn minerals, thus increasing Mn availability in soil. The present study aimed to assess the Mn solubilizing ability and plant growth-promoting potential of Bacillus spp. strains for maize plants with insoluble Mn compounds. Several Mn-solubilizing bacterial (MSB) strains were isolated from the maize rhizosphere using nutrient agar media amended with 50 mM MnO₂. These strains were screened based on qualitative and quantitative solubilization of Mn, phosphorus, potassium, and zinc and production of ammonia. The majority of MSB strains were positive for catalase, protease, amylase, and oxidase activity, while more than 60% of tested strains were positive for lipase activity, and the production of indole-3-acetic acid and siderophores. Forty-five percent of the tested strains also showed solubilization of potassium. All the MSB strains were evaluated for their ability to promote plant growth and Mn uptake in the presence of MnO₂ under axenic sand culture conditions. The results revealed that inoculation with MSB strains under sand culture significantly improved the growth of maize seedlings except for strains ASH7, ASH10, and ASH12. Comparatively, strains ASH6, ASH11, ASH19, ASH20, and ASH22 demonstrated a better increase in plant growth, fresh and dry biomass, and Mn uptake in roots and shoots than the other strains tested. All of these strains were identified as Bacillus spp. through 16S rRNA partial gene sequencing. Maize inoculation with these selected identified MSB strains also resulted in an increase in maize growth and nutrient uptake in maize roots and shoots under soil culture conditions in the presence of native soil Mn. The current study highlights the importance of MSB strain inoculation which could be a potential bioinoculants to promote plant growth under Mn deficiency.

Pioneer trees of Betula pendula at a red gypsum landfill harbour specific structure and composition of root-associated microbial communities

The study of root-associated microbial communities is important to understand the natural processes involved in plant recolonisation at degraded areas. Root associated bacterial and fungal communities of woody species colonising a red gypsum landfill (a metal-enriched environment) were characterised through metabarcoding. Among trees naturally growing on the landfill, Betula pendula is the only tree species in the centre of the area, whereas companion tree species such as Populus nigra, P. tremula and Salix purpurea were present on the edges. The bacterial community was dominated by Proteobacteria (38%), Actinobacteria (35%) and Bacteroidetes (20%) and the most abundant bacterial OTU belonged to the family Streptomycetaceae. The fungal community was dominated by Ascomycota (60%) and Basidiomycota (30%) and the most abundant family was Pyronemataceae. Analysis of similarities, heatmap and hierarchical cluster analysis showed that B. pendula grown in the centre of the landfill harboured a specific microbial community, which was unique and different, not only from other tree species (Populus or Salix spp.), but also from other B. pendula growing at the edges. Our findings on relevant indicator OTUs associated to the birches located in the centre of the landfill (such as Otu00716 Catellatospora sp. (family Micromonosporaceae, phylum Actinobacteria) or Otu4_35502 Russula sp. (family Russulaceae, phylum Basidiomycota)) may have important implications for the successful revegetation of these harsh environments using microbial-based phytostabilisation approaches.

Metagenomic insights into the microbial diversity in manganese-contaminated mine tailings and their role in biogeochemical cycling of manganese

To extend the knowledge on the microbial diversity of manganese rich environments, we performed a clone library based study using metagenomic approach. Pyrosequencing based analysis of 16S rRNA genes were carried out on an Illumina platform to gain insights into the bacterial community inhabiting in a manganese mining site and the taxonomic profiles were correlated with the inherent capacities of these strains to solubilise manganese. The application of shot gun sequencing in this study yielded results which revealed the highest prevalence of Proteobacteria (42.47%), followed by Actinobacteria (23.99%) in the area of study. Cluster of orthologous group (COG) functional category has 85,066 predicted functions. Out of which 11% are involved in metabolism of amino acid, 9% are involved in production and conversion of energy while Keto Encyclopedia of Gene and Genomes (KEGG) functional category has 107,388 predicted functions, out of which 55% are involved in cellular metabolism, 15% are environmental and information processing and 12% are genetic information processing in nature. The isolated microbial consortia demonstrated visible growth in presence of high concentrations of Mn. Solubilisation studies resulted in 86% of manganese recovery after 20 days. The result presented in this study has important implications in understanding the microbial diversity in manganese contaminated mine tailings and their role in natural geochemical cycling of Mn.

Tolerance and growth kinetics of bacteria isolated from gold and gemstone mining sites in response to heavy metal concentrations

Response and growth kinetics of microbes in contaminated medium are useful indices for the screening and selection of tolerant species for eco-friendly bio-augmentative remediation of polluted environments. In this study, the heavy metal (HM) tolerance, bioaccumulation and growth kinetics of seven bacterial strains isolated from mining sites to 10 HMs (Cd, Hg, Ni, Al, Cr, Pb, Cu, Fe, Mn and Zn) at varied concentrations (25-600 mgL^-1) were investigated. The isolates were phylogenetically (16S rRNA gene) related to Lysinibacillus macroides, Achromobacter spanius, Bacillus kochii, B. cereus, Klebsiella pneumoniae, Pseudomonas mosselii and P. nitroreducens. Metal tolerance, effects on lag phase duration and growth rates were assessed using the 96-well micro-titre method. Furthermore, metal bioaccumulation and quantities within cells were determined by transmission electron microscopy and electron dispersive x-ray analyses. Tolerance to Ni, Pb, Fe and Mn occurred at highest concentrations tested. Growth rates increased with increasing Fe concentrations, but reduced significantly (p < .05) with increasing Zn, Cu, Hg, Cd and Al. Significantly higher (p < .05) growth rates (compared to controls) was found with some isolates in Hg (25 mgL^-1), Ni (100 mgL^-1), Cr (150 mgL^-1), Mn (600 mgL^-1), Pb (100 mgL^-1), Fe (600 mgL^-1) and Al (50 mgL^-1). Lag phase urations were isolate- and heavy metal-specific, in direct proportion to concentrations. A. spanius accumulated the most Mn and Zn, while B. cereus accumulated the most Cu. Metals accumulated intra-cellularly without cell morphology distortions. The isolates' multi-metal tolerance, intra-cellular metal bioaccumulation and growth kinetics suggest potentials for application in the synergetic biodegradation and bioremediation of polluted environments, especially HM-rich sites.