Mobilization of manganese by basalt associated Mn(II)-oxidizing bacteria from the Indian Ridge System

Mixed agricultural, industrial, and domestic drainage water discharge poses a massive strain on freshwater ecosystems: a case from the Nile River in Upper Egypt

Heavy metal and pesticide pollution of freshwater ecosystems, i.e., rivers, raises significant concerns worldwide, where practical solutions to reduce the threats become urgent need. Heavy metals and pesticides are top of the list of environmental toxicants endangering nature; therefore, pesticides and heavy metals were measured at 10 stations along the Al-Zennar agricultural drain and the Nile River at Assiut city in Upper Egypt, to assess potential negative impact on the water/sediment's quality. The sediment of the streambed is a sink for pesticides and heavy metals, where both water and sediments have higher contamination factor (CF) for Cd, Pb, Cr, Cu, and Zn. In addition, the Nile water is highly contaminated by PCBs. The distance to the point source and hydrodynamics (flow rate and stream gradient) has major influences in pollutant concentrations as indicated by regression models. Dilution effect and rapid sedimentation may comment on the lower concentrations of the pollutants in the Nile comparatively to the drain and on the water comparatively to the sediments. The physiochemistry of the stations has minor effect on the metal/pesticide concentration, where the variable importance of projection (VIP) of the partial least square model indicated that total dissolved solids (TDS), total suspended solids (TSS), SO42-, and BOD/TOC/COD are the main contributors to the metal/pesticide concentration. Concentrations were not correlated between water and sediment suggesting a historical accumulation in sediments and temporal variation in the pollution load in the Al-Zennar drain. Bray-Curtis clustering confirmed that heavy metals have the same anthropogenic source in contrast to natural source of both Mn and Fe.

A Review of Manganese-Oxidizing Bacteria (MnOB): Applications, Future Concerns, and Challenges

Groundwater serving as a drinking water resource usually contains manganese ions (Mn2+) that exceed drinking standards. Based on the Mn biogeochemical cycle at the hydrosphere scale, bioprocesses consisting of aeration, biofiltration, and disinfection are well known as a cost-effective and environmentally friendly ecotechnology for removing Mn2+. The design of aeration and biofiltration units, which are critical components, is significantly influenced by coexisting iron and ammonia in groundwater; however, there is no unified standard for optimizing bioprocess operation. In addition to the groundwater purification, it was also found that manganese-oxidizing bacteria (MnOB)-derived biogenic Mn oxides (bioMnOx), a by-product, have a low crystallinity and a relatively high specific surface area; the MnOB supplied with Mn2+ can be developed for contaminated water remediation. As a result, according to previous studies, this paper summarized and provided operational suggestions for the removal of Mn2+ from groundwater. This review also anticipated challenges and future concerns, as well as opportunities for bioMnOx applications. These could improve our understanding of the MnOB group and its practical applications.

Manganese oxidation and prokaryotic community analysis in a polycaprolactone-packed aerated biofilm reactor operated under seawater conditions

Biogenic manganese oxides (BioMnOx) have been receiving increasing attention for the removal of environmental contaminants and recovery of minor metals from water environments. However, the enrichment of heterotrophic Mn(II)-oxidizing microorganisms for BioMnOx production in the presence of fast-growing coexisting heterotrophs is challenging. In our previous work, we revealed that polycaprolactone (PCL), a biodegradable aliphatic polyester, can serve as an effective solid organic substrate to enrich Mn-oxidizing microbial communities under seawater conditions. However, marine BioMnOx-producing bioreactor systems utilizing PCL have not yet been established. Therefore, a laboratory-scale continuous-flow PCL-packed aerated biofilm (PAB) reactor was operated for 238 days to evaluate its feasibility for BioMnOx production under seawater conditions. After the start-up of the reactor, the average dissolved Mn removal rates of 0.4-2.3 mg/L/day, likely caused by Mn(II) oxidation, were confirmed under different influent dissolved Mn concentrations (2.5-14.0 mg/L on average) and theoretical hydraulic retention time (0.19-0.77 day) conditions. The 16S rRNA gene amplicon sequencing analysis suggested the presence of putative Mn(II)-oxidizing and PCL-degrading bacterial lineages in the reactor. Two highly dominant operational units (OTUs) in the packed PCL-associated biofilm were assigned to the genera Marinobacter and Pseudohoeflea, whereas the genus Lewinella and unclassified Alphaproteobacteria OTUs were highly dominant in the MnOx-containing black/dark brown precipitate-associated biofilm formed in the reactor. Excitation-emission matrix fluorescence spectroscopy analysis revealed the production of tyrosine- and tryptophane-like components, which may serve as soluble heterotrophic organic substrates in the reactor. Our findings indicate that PAB reactors are potentially applicable to BioMnOx production under seawater conditions.

The “Infernaccio” Gorges: Microbial Diversity of Black Deposits and Isolation of Manganese-Solubilizing Bacteria

Simple Summary

“Infernaccio” gorges are one of the Earth’s hidden habitats in Central Italy. Beyond the deep incisions and high slopes, these gorges are characterized by black deposits in gorge walls and covering rock surfaces. Several geological events have shaped these unique geological formations and their microbiota. This study investigated microbial contribution to black deposit formation and isolating Mn-oxide-solubilizing bacteria. Our results provided evidence of the putative role of Bacteria and Archaea in forming manganese oxide deposits. Findings also showed that these deposits are a source of valuable strains with manganese oxide bioleaching properties, essential for bioremediation and metal recovery.

Abstract

The present study explored the microbial diversity of black deposits found in the “Infernaccio” gorge. X-ray Powdered Diffraction (XRPD) was used to investigate the crystallinity of the samples and to identify the minerals. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDS) were used to detect the bacterial imprints, analyze microbe–mineral interactions, and highlight the chemical element distribution in the black deposits. 16S rRNA gene metabarcoding allowed the study of Archaea and Bacteria communities. Mn-oxide-solubilizing isolates were also obtained and characterized by culturable and molecular approaches. The multidisciplinary approach showed the occurrence of deposits composed of birnessite, diopside, halloysite, and leucite. Numerous bacterial imprints confirmed the role of microorganisms in forming these deposits. The Bacteria and Archaea communities associated with these deposits and runoff waters are dynamic and shaped by seasonal changes. The uncultured and unknown taxa are the most common and abundant. These amplicon sequence variants (ASVs) were mainly assigned to Proteobacteria and Bacteroidetes phyla. Six isolates showed interesting Mn solubilization abilities under microaerophilic conditions. Molecular characterization associated isolates to Brevibacterium, Bacillus, Neobacillus, and Rhodococcus genera. The findings enriched our knowledge of geomicrobiological aspects of one of the Earth’s hidden habitats. The study also unveiled the potential of this environment as an isolation source of biotechnologically relevant bacteria.

Mineralogical and Genomic Constraints on the Origin of Microbial Mn Oxide Formation in Complexed Microbial Community at the Terrestrial Hot Spring

Manganese (Mn) oxides are widespread on the surface environments of the modern Earth. The role of microbial activities in the formation of Mn oxides has been discussed for several decades. However, the mechanisms of microbial Mn oxidation, and its role in complex microbial communities in natural environments, remain uncertain. Here, we report the geochemical, mineralogical, and metagenomic evidence for biogenic Mn oxides, found in Japanese hot spring sinters. The low crystallinity of Mn oxides, and their spatial associations with organic matter, support the biogenic origin of Mn oxides. Specific multicopper oxidases (MCOs), which are considered Mn-oxidizing enzymes, were identified using metagenomic analyses. Nanoscale nuggets of copper sulfides were, also, discovered in the organic matter in Mn-rich sinters. A part of these copper sulfides most likely represents traces of MCOs, and this is the first report of traces of Mn-oxidizing enzyme in geological samples. Metagenomic analyses, surprisingly, indicated a close association of Mn oxides, not only in aerobic but also in anaerobic microbial communities. These new findings offer the unique and unified positions of Mn oxides, with roles that have not been ignored, to sustain anaerobic microbial communities in hot spring environments.

Manganese facilitates cadmium stabilization through physicochemical dynamics and amino acid accumulation in rice rhizosphere under flood-associated low pe+pH

Periodic flooding in paddy soils impacts redox behavior and induces variations in pe+pH levels. Manganese (Mn) is capable of reducing cadmium (Cd) uptake by rice. However, the processes involved in how Mn alters Cd mobilization under different pe+pH environments remain poorly understood. To investigate the mechanisms of Mn-mediated soil Cd-stabilization and subsequent inhibition of Cd uptake from flooded soils, we examined Cd immobilization in soil pot incubations, transcriptional changes in Cd-transport genes, and metabolomic analyses of roots and rhizosphere soils with or without Mn application. We found a decrease in extractable Cd concentration largely depended on irrigation-associated low pe+pH, exogenous Mn enhancement of Fe-Mn (oxyhydro)oxide-mediated Cd transformation, and Cd deposition in rice Fe/Mn plaques. Mn application led to striking effects on the expression of Cd-related genes eg. IRT, HMA, and NRAMP in rice root tissue. Exposure to Mn under variable pe+pH levels resulted in metabolic reprogramming of soil and rice roots. Mn induced amino acid synthesis in rice roots, leading to rhizosphere accumulation of free L-lysine, glycine, and glutamine, which can reportedly bind metal ions, forming complexes with Cd. Thus, secreted amino acids, low pe+pH, and free Mn can together comprise a multi-faceted approach to managing Cd toxicity in rice.

A manganese-oxidizing bacterial consortium and its biogenic Mn oxides for dye decolorization and heavy metal adsorption

Manganese (Mn) contamination is a common environmental problem in the world and manganese oxidizing bacteria (MOB) play important roles in bioremediation of heavy metal and organic pollution. In this study, a novel MOB consortium AS containing core microbes of Sphingobacterium and Bacillus was acclimated from Mn-contaminated rivulet sediments. The MOB consortium AS presented good Mn(II) removal performance under 500-10,000 mg/L Mn(II), with Mn(II) removal capacities ranging from 481 to 3478 mg/L. In coexistence systems of Mn(II) and Fe(II), Ni(II), Cu(II), and Zn(II), the MOB consortium AS removed 98%, 91%, 99%, and 76% of Mn(II), respectively. Additionally, the MOB consortium AS could utilize multiple carbon sources (e.g., Chitosan, β-Cyclodextrin, and Phenanthrene) to remove Mn(II), with Mn(II) removal efficiencies ranging from 11% to 97%. Meanwhile, XRD, XPS, FTIR, SEM, and EDS analyses reflected that biogenic Mn oxides (bio-MnOx-C) contained C, O, Mn (Mn(II) and Mn(IV)) and embodied in rhodochrosite and birnessite. The bio-MnOx-C exhibited second-order kinetic reaction for removal of dye, with corresponding decolorization capacities of 22.0 mg/g for methylene blue and 23.8 mg/g for crystal violet. In addition, bio-MnOx-C showed adsorption capacities of 159.0 mg/g for Cu(II), 130.7 mg/g for Zn(II), and 123.3 mg/g for Pb(II). Overall, this study illustrates consortium AS and bio-MnOx-C have great potentials in remediation of pollution caused by heavy metals and organic pollutants.

Discovery of a novel native bacterium of Providencia sp. with high biosorption and oxidation ability of manganese for bioleaching of heavy metal contaminated soils

Heavy metal removal from contaminated soils is a long-term challenging problem important for global economics, environment, and human health. Marine and freshwater-originated Mn(II)-oxidizing bacteria are considered as the promising bioremediation agents for environmental applications. However, practical application of soil-originated Mn(II)-oxidizing bacteria remains to be developed for contaminated soil remediation. In this work, the Mn(II) biosorption/oxidation mechanism of a new soil-originated bacterium and its bioleaching efficiency of heavy metals from soils was studied in detail. First, we found, isolated and identified a new highly Mn(II)-tolerant bacterial strain Providencia sp. LLDRA6 from heavy metal-contaminated soils. Next, strain LLDRA6 demonstrated its high Mn(II) biosorption capacity in aqueous solution. Then, Mn(II) adsorption by LLDRA6 was largely proven to be a synergistic effect of (i) Mn(II) precipitation on the cell surface, (ii) oxidation of Mn(II) into BioMnO_x on the cell surface, and (iii) intracellular accumulation of insoluble MnCO₃. Finally, combination bioleaching by the bacterium of Providencia sp. LLDRA6 and its formed BioMnO_x was proposed to develop a potential environment-friendly and cost-effective technique to remediate severely heavy metal-contaminated soils. The bioleaching tests demonstrated that the combination of Providencia sp. LLDRA6 and BioMnO_x exhibited an excellent removal efficiency for heavy metals of Pb (81.72%), Cr (88.29%), Cd (90.34%), Cu (91.25%), Mn (56.13%), and Zn (59.83%) from contaminated soils, resulting in an increase of removal efficiency in the range of 1.68-26.4% compared to Providencia sp. LLDRA6 alone. Moreover, the bacterial leachate facilitated the residual fraction of metals to transform into the easily migratory fractions in soils. These findings have demonstrated that strain LLDRA6 has high adsorption ability to remove heavy metals from contaminated soils, thus providing a promising bio-adsorbent for environmental bioremediation.

Removal of Manganese(II) from Acid Mine Wastewater: A Review of the Challenges and Opportunities with Special Emphasis on Mn-Oxidizing Bacteria and Microalgae

Many global mining activities release large amounts of acidic mine drainage with high levels of manganese (Mn) having potentially detrimental effects on the environment. This review provides a comprehensive assessment of the main implications and challenges of Mn(II) removal from mine drainage. We first present the sources of contamination from mineral processing, as well as the adverse effects of Mn on mining ecosystems. Then the comparison of several techniques to remove Mn(II) from wastewater, as well as an assessment of the challenges associated with precipitation, adsorption, and oxidation/filtration are provided. We also critically analyze remediation options with special emphasis on Mn-oxidizing bacteria (MnOB) and microalgae. Recent literature demonstrates that MnOB can efficiently oxidize dissolved Mn(II) to Mn(III, IV) through enzymatic catalysis. Microalgae can also accelerate Mn(II) oxidation through indirect oxidation by increasing solution pH and dissolved oxygen production during its growth. Microbial oxidation and the removal of Mn(II) have been effective in treating artificial wastewater and groundwater under neutral conditions with adequate oxygen. Compared to physicochemical techniques, the bioremediation of manganese mine drainage without the addition of chemical reagents is relatively inexpensive. However, wastewater from manganese mines is acidic and has low-levels of dissolved oxygen, which inhibit the oxidizing ability of MnOB. We propose an alternative treatment for manganese mine drainage that focuses on the synergistic interactions of Mn in wastewater with co-immobilized MnOB/microalgae.

Diversity and extracellular enzyme activities of heterotrophic bacteria from sediments of the Central Indian Ocean Basin

Sedimentary bacteria play a role in polymetallic nodule formation and growth. There are, however, limited reports on bacterial diversity in nodule-rich areas of the Central Indian Ocean Basin (CIOB). In this study, bacterial abundance in thirteen sediment cores collected from the CIOB was enumerated, followed by phylogenetic characterisation and, screening of select heterotrophic bacteria for extracellular enzyme activities. Total bacterial counts (TBC) were in the order of 10⁷ cells g^-1; there was a significant difference (p > 0.05) among the cores but not within the sub-sections of the cores. The retrievable heterotrophic counts ranged from non-detectable to 5.33 × 10⁵ g^-1; the heterotrophic bacteria clustered within the phyla Firmicutes, Proteobacteria and Actinobacteria. Bacillus was the most abundant genus. The extracellular enzyme activities were in the order: amylase > lipase > protease > phosphatase > Dnase > urease. Major findings are compared with previous studies from the CIOB and other areas.

Identification of Cultivable Bacteria from Tropical Marine Sponges and Their Biotechnological Potentials

Marine sponges are acknowledged as bacterial hotspots in the oceanic biome. Aquatic bacteria are being investigated comprehensively for bioactive complexes and secondary metabolites. Cultivable bacteria associated with different species of sea sponges in South China Sea waters adjacent to Bidong Island, Terengganu were identified. Molecular identification was accomplished using 16S rRNA gene cloning and sequencing. Fourteen bacterial species were identified and their phylogenetic relationships were analysed by constructing a neighbour-joining tree with Molecular Evolutionary Genetics Analysis 6. The identified species encompassed four bacterial classes that were Firmicutes, Actinobacteria, Alphaproteobacteria and Gammaproteobacteria known to have been associated with sponges. The potential biotechnological applications of the identified bacteria were compared and reviewed based on relevant past studies. The biotechnological functions of the 14 cultivable isolates have been previously reported, hence reinforcing that bacteria associated with sponges are an abundant resource of scientifically essential compounds. Resilience of psychrotolerant bacteria, Psychrobacter celer, in warm tropical waters holds notable prospects for future research.

Microbiome analysis reveals the abundance of bacterial pathogens in Rousettus leschenaultii guano

Bats are crucial for proper functioning of an ecosystem. They provide various important services to ecosystem and environment. While, bats are well-known carrier of pathogenic viruses, their possible role as a potential carrier of pathogenic bacteria is under-explored. Here, using culture-based approach, employing multiple bacteriological media, over thousand bacteria were cultivated and identified from Rousettus leschenaultii (a frugivorous bat species), the majority of which were from the family Enterobacteriaceae and putative pathogens. Next, pathogenic potential of most frequently cultivated component of microbiome i.e. Escherichia coli was assessed to identify its known pathotypes which revealed the presence of virulent factors in many cultivated E. coli isolates. Applying in-depth bacterial community analysis using high-throughput 16 S rRNA gene sequencing, a high inter-individual variation was observed among the studied guano samples. Interestingly, a higher diversity of bacterial communities was observed in decaying guano representative. The search against human pathogenic bacteria database at 97% identity, a small proportion of sequences were found associated to well-known human pathogens. The present study thus indicates that this bat species may carry potential bacterial pathogens and advice to study the effect of these pathogens on bats itself and the probable mode of transmission to humans and other animals.

Pore Mn²⁺ dynamics of the rhizosphere of flooded and non-flooded rice during a long wet and drying phase in two rice growing soils

Flooded rice soils produce elevated concentrations of soluble manganous manganese (Mn(2+)) that could be potentially toxic to subsequent crops. To provide insight into how soil pore Mn(2+) changes its concentration in a rice and post rice drying soil, we used an artificial microcosm system to follow Mn(2+) concentrations in two different soil types (red sodosol and grey vertosol) and under two irrigation regimes (flooded and saturated). Soil pore water was collected from four different depths of soil (2.5 cm, 7.5 cm, 15 cm and 25 cm) and Mn(2+) concentrations were analysed during and after the rice phase over a one year cycle. Mn(2+) increased with the advancement of anaerobic conditions at all soil depths, but the concentration was higher in flooded soil compared to saturated soil. Initially, the highest concentration of Mn(2+) was found at a depth of 7.5 cm, while at the later stage of rice growth, more Mn(2+) was found in the deepest sampling depth (25 cm). Plants grown in saturated soils showed a delay in flowering of approximately 3 weeks compared to flooded cultures. Moreover, plants grown in flooded soil produced more tillers and leaf area than those grown in saturated soil. Peak concentrations of soil Mn(2+) were associated with the reproductive stage of rice growth. Mn(2+) concentrations decreased after drainage of water. In post rice soils, Mn(2+) remained elevated for some time (lag phase), and then rapidly declined. Regression analysis revealed that the process of oxidation of Mn(2+) to Mn(4+) following water drainage decreased with soil depth.