Carbon and steel surfaces modified by Leptothrix discophora SP-6: characterization and implications

Impact of corrosion inhibitors on antibiotic resistance, metal resistance, and microbial communities in drinking water

Corrosion inhibitors, including zinc orthophosphate, sodium orthophosphate, and sodium silicate, are commonly used to prevent the corrosion of drinking water infrastructure. Metals such as zinc are known stressors for antibiotic resistance selection, and phosphates can increase microbial growth in drinking water distribution systems (DWDS). Yet, the influence of corrosion inhibitor type on antimicrobial resistance in DWDS is unknown. Here, we show that sodium silicates can decrease antibiotic resistant bacteria (ARB) and antibiotic-resistance genes (ARGs), while zinc orthophosphate increases ARB and ARGs in source water microbial communities. Based on controlled bench-scale studies, zinc orthophosphate addition significantly increased the abundance of ARB resistant to ciprofloxacin, sulfonamides, trimethoprim, and vancomycin, as well as the genes sul1, qacEΔ1, an indication of resistance to quaternary ammonium compounds, and the integron-integrase gene intI1. In contrast, sodium silicate dosage at 10 mg/L resulted in decreased bacterial growth and antibiotic resistance selection compared to the other corrosion inhibitor additions. Source water collected from the drinking water treatment plant intake pipe resulted in less significant changes in ARB and ARG abundance due to corrosion inhibitor addition compared to source water collected from the pier at the recreational beach. In tandem with the antibiotic resistance shifts, significant microbial community composition changes also occurred. Overall, the corrosion inhibitor sodium silicate resulted in the least selection for antibiotic resistance, which suggests it is the preferred corrosion inhibitor option for minimizing antibiotic resistance proliferation in DWDS. However, the selection of an appropriate corrosion inhibitor must also be appropriate for the water chemistry of the system (e.g., pH, alkalinity) to minimize metal leaching first and foremost and to adhere to the lead and copper rule. IMPORTANCE Antibiotic resistance is a growing public health concern across the globe and was recently labeled the silent pandemic. Scientists aim to identify the source of antibiotic resistance and control points to mitigate the spread of antibiotic resistance. Drinking water is a direct exposure route to humans and contains antibiotic-resistant bacteria and associated resistance genes. Corrosion inhibitors are added to prevent metallic pipes in distribution systems from corroding, and the type of corrosion inhibitor selected could also have implications on antibiotic resistance. Indeed, we found that sodium silicate can minimize selection of antibiotic resistance while phosphate-based corrosion inhibitors can promote antibiotic resistance. These findings indicate that sodium silicate is a preferred corrosion inhibitor choice for mitigation of antibiotic resistance.

Current overview and future perspective in fungal biorecovery of metals from secondary sources

Microorganisms are intimately involved in many biogeochemical processes that underpin the transformation of metals and cycling of related substances, such as metalloids and radionuclides. Many processes determine the mobility and bioavailability of metals, thereby influencing their transfer to the environment and living organisms. These processes are closely related to global phenomena such as soil formation and bioweathering. In addition to environmental significance, microbial metal transformations play an essential role in both in situ and ex situ bioremediation processes for solid and liquid wastes. The solubilization of heavy metals from industrial waste and soil is commonly used in bioremediation. Moreover, immobilization processes are applicable to bioremediation of metals and radionuclides from aqueous solutions. This review provides an overview of critical metal extraction and recovery from secondary sources, applied microorganisms and methods, metal-microbe interactions, as well as a detailed description of known metal recovery mechanisms.

Insights into Advancements and Electrons Transfer Mechanisms of Electrogens in Benthic Microbial Fuel Cells

Benthic microbial fuel cells (BMFCs) are a kind of microbial fuel cell (MFC), distinguished by the absence of a membrane. BMFCs are an ecofriendly technology with a prominent role in renewable energy harvesting and the bioremediation of organic pollutants through electrogens. Electrogens act as catalysts to increase the rate of reaction in the anodic chamber, acting in electrons transfer to the cathode. This electron transfer towards the anode can either be direct or indirect using exoelectrogens by oxidizing organic matter. The performance of a BMFC also varies with the types of substrates used, which may be sugar molasses, sucrose, rice paddy, etc. This review presents insights into the use of BMFCs for the bioremediation of pollutants and for renewable energy production via different electron pathways.

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.

Electron transfer mechanisms, new applications, and performance of biocathode microbial fuel cells

Broad application of microbial fuel cells (MFCs) requires low cost and high operational sustainability. Microbial-cathode MFCs, or cathodes using only bacterial catalysts (biocathodes), can satisfy these demands and have gained considerable attention in recent years. Achievements with biocathodes over the past 3-4 years have been particularly impressive not only with respect to the biological aspects but also the system-wide considerations related to electrode materials and solution chemistry. The versatility of biocathodes enables us to use not only oxygen but also contaminants as possible electron acceptors, allowing nutrient removal and bioremediation in conjunction with electricity generation. Moreover, biocathodes create opportunities to convert electrical current into microbially generated reduced products. While many new experimental results with biocathodes have been reported, we are still in the infancy of their engineering development. This review highlights the opportunities, limits, and challenges of biocathodes.

Electricity generation using chocolate industry wastewater and its treatment in activated sludge based microbial fuel cell and analysis of developed microbial community in the anode chamber

Feasibility of using chocolate industry wastewater as a substrate for electricity generation using activated sludge as a source of microorganisms was investigated in two-chambered microbial fuel cell. The maximum current generated with membrane and salt bridge MFCs was 3.02 and 2.3 A/m(2), respectively, at 100 ohms external resistance, whereas the maximum current generated in glucose powered MFC was 3.1 A/m(2). The use of chocolate industry wastewater in cathode chamber was promising with 4.1 mA current output. Significant reduction in COD, BOD, total solids and total dissolved solids of wastewater by 75%, 65%, 68%, 50%, respectively, indicated effective wastewater treatment in batch experiments. The 16S rDNA analysis of anode biofilm and suspended cells revealed predominance of beta-Proteobacteria clones with 50.6% followed by unclassified bacteria (9.9%), alpha-Proteobacteria (9.1%), other Proteobacteria (9%), Planctomycetes (5.8%), Firmicutes (4.9%), Nitrospora (3.3%), Spirochaetes (3.3%), Bacteroides (2.4%) and gamma-Proteobacteria (0.8%). Diverse bacterial groups represented as members of the anode chamber community.

Recent developments in microbial fuel cell technologies for sustainable bioenergy

Microbial fuel cells (MFCs) are devices that exploit microbial catabolic activities to generate electricity from a variety of materials, including complex organic waste and renewable biomass. These sources provide MFCs with a great advantage over chemical fuel cells that can utilize only purified reactive fuels (e.g., hydrogen). A developing primary application of MFCs is its use in the production of sustainable bioenergy, e.g., organic waste treatment coupled with electricity generation, although further technical developments are necessary for its practical use. In this article, recent advances in MFC technologies that can become fundamentals for future practical MFC developments are summarized. Results of recent studies suggest that MFCs will be of practical use in the near future and will become a preferred option among sustainable bioenergy processes.

MEMS and the microbe

In recent years, relatively simple MEMS fabrications have helped accelerate our knowledge of the microbial cell. Current progress and challenges in the application of lab-on-a-chip devices to the viable microbe are reviewed. Furthermore, the degree to which microbiologists are becoming the engineers and are tailoring microbial cells and protocells as potential components for bioMEMS devices is highlighted. We conclude this is a highly productive time for microbiologists and microengineers to unite their shared interest in the micron scale world.