Metabolic regulation of Shewanella oneidensis for microbial electrosynthesis: From extracellular to intracellular.

Shewanella oneidensis MR-1 (S. oneidensis MR-1) has been shown to benefit from microbial electrosynthesis (MES) due to its exceptional electron transfer efficiency. In this study, genes involved in both extracellular electron uptake (EEU) and intracellular CO2 conversion processes were examined and regulated to enhance MES performance. The key genes identified for MES in the EEU process were mtrB, mtrC, mtrD, mtrE, omcA and cctA. Overexpression of these genes resulted in 1.5-2.1 times higher formate productivity than that of the wild-type strains (0.63 mmol/(L·µg protein)), as 0.94-1.61 mmol/(L·µg protein). In the intracellular CO2 conversion process, overexpression of the nadE, nadD, nadR, nadV, pncC and petC genes increased formate productivity 1.3-fold-3.4-fold. Moreover, overexpression of the formate dehydrogenase genes fdhA1, fdhB1 and fdhX1 in modified strains led to a 2.3-fold-3.1-fold increase in formate productivity compared to wild-type strains. The co-overexpression of cctA, fdhA1 and nadV in the mutant strain resulted in 5.59 times (3.50 mmol/(L·µg protein)) higher formate productivity than that of the wild-type strains. These findings revealed that electrons of MES derived from the electrode were utilized in the energy module for synthesizing ATP and NADH, followed by the synthesis of formate in formate dehydrogenase by the combinatorial effects of ATP, NADH, electrons and CO2. The results provide new insights into the mechanism of MES in S. oneidensis MR-1 and pave the way for genetic improvements that could facilitate the further application of MES.

Sustainable Conversion of Microplastics to Methane with Ultrahigh Selectivity by a Biotic-Abiotic Hybrid Photocatalytic System.

Efficient conversion of microplastics into fuels provides a promising strategy to alleviate environmental pollution and the energy crisis. However, the conventional processes are challenged by low product selectivity and potential secondary pollution. Herein, a biotic-abiotic photocatalytic system is designed by assembling Methanosarcina barkeri (M. b) and carbon dot-functionalized polymeric carbon nitrides (CDPCN), by which biodegradable microplastics-poly(lactic acid) after heat pretreatment can be converted into CH4 for five successive 24-day cycles with nearly 100 % CH4 selectivity by the assistance of additional CO2 . Mechanistic analyses showed that both photooxidation and photoreduction methanogenesis worked simultaneously via the fully utilizing photogenerated holes and electrons without chemical sacrificial quenchers. Further research validated the real-world applicability of M. b-CDPCN for non-biodegradable microplastic-to-CH4 conversion, offering a new avenue for engineering the plastic reuse.

Nano-sized Fe2O3/Fe3O4 facilitate anaerobic transformation of hexavalent chromium in soil-water systems.

The purpose of this study is to investigate the effects of nano-sized or submicro Fe2O3/Fe3O4 on the bioreduction of hexavalent chromium (Cr(VI)) and to evaluate the effects of nano-sized Fe2O3/Fe3O4 on the microbial communities from the anaerobic flooding soil. The results indicated that the net decreases upon Cr(VI) concentration from biotic soil samples amended with nano-sized Fe2O3 (317.1±2.1mg/L) and Fe3O4 (324.0±22.2mg/L) within 21days, which were approximately 2-fold of Cr(VI) concentration released from blank control assays (117.1±5.6mg/L). Furthermore, the results of denaturing gradient gel electrophoresis (DGGE) and high-throughput sequencing indicated a greater variety of microbes within the microbial community in amendments with nano-sized Fe2O3/Fe3O4 than the control assays. Especially, Proteobacteria occupied a predominant status on the phylum level within the indigenous microbial communities from chromium-contaminated soils. Besides, some partial decrease of soluble Cr(VI) in abiotic nano-sized Fe2O3/Fe3O4 amendments was responsible for the adsorption of nano-sized Fe2O3/Fe3O4 to soluble Cr(VI). Hence, the presence of nano-sized Fe2O3/Fe3O4 could largely facilitate the mobilization and biotransformation of Cr(VI) from flooding soils by adsorption and bio-mediated processes.

Role of nanoparticles in controlling arsenic mobilization from sediments near a realgar tailing.

Microcosm experiments were conducted to investigate the mechanism of microbial-mediated As mobilization from high arsenic tailing sediments amended with nanoparticles (NPs). The addition of SiO2 NPs could substantially stimulate arsenic mobilization in the sodium acetate amendment sediments. However, the addition of Fe2O3 and Fe3O4 NPs restrained arsenic release because these NPs resulted in Fe-As coprecipiate. Moreover, NP additions in sediments amended with sodium acetate as the electron donor clearly promoted microbial dissimilatory iron reduction. Nearly 4 times the Fe(II) (11.67-12.87 mg·L(-1)) from sediments amended with NPs and sodium acetate was released compared to sediments amended with only sodium acetate (3.49 mg·L(-1)). Based on molecular fingerprinting and sequencing analyses, the NP additions could potentially change the sediment bacterial community composition and increase the abundance of Fe(III) and As(V) reduction bacteria. Several potential NP-stimulated bacteria were related to Geobacter, Anaeromyxobacter, Clostridium, and Alicyclobacillus. The findings offer a relatively comprehensive assessment of NP (e.g., Fe2O3, Fe3O4, and SiO2) effects on sediment bacterial communities and As mobilization.

Microplastics in the soil environment: Focusing on the sources, its transformation and change in morphology.

Microplastics (MPs) are small plastic pieces less than 5 mm in size. Previous studies have focused on the sources, transports, and fates of MPs in marine or sediment environments. However, limited attention has been given to the role of land as the primary source of MPs, and how plastic polymers are transformed into MPs through biological or abiotic effects during the transport process remains unclear. Here, we focus on the exploration of the main sources of MPs in the soil, highlighting that MP generation is not solely a byproduct of plastic production but can also result from the impact of biological and abiotic factors during the process of MPs transport. This review presents a new perspective on understanding the degradation of MPs in soil, considering soil as a distinct fluid and suggesting that the main transformation and change mediated by abiotic factors occur on the soil surface, while the main biodegradation occurs in the soil interior. This viewpoint is suggested because the role of some abiotic factors becomes less obvious in the soil interior, and MPs, whose surface is expected to colonize microorganisms, are gradually considered a carbon source independent of photosynthesis and net primary production. This review emphasizes the need to understand basic MPs information in soil for a rational evaluation of its environmental toxicity. Such understanding enables better control of MPs pollution in affected areas and prevents contamination in unaffected regions. Finally, knowledge gaps and future research directions necessary for advancements in this field are provided.

Complete Genome Sequence of Tissierella sp. Strain Yu-01, Isolated from the Feces of the Black Soldier Fly.

We report the complete genome sequence of Tissierella sp. strain Yu-01 (=BCRC 81391), isolated from the feces of black soldier fly (Hermetia illucens) larvae. This fly has increasingly been gaining attention because of its usefulness for recycling organic waste. The genome of strain Yu-01 was selected for further species delineation.

The effect of recycling flux on the performance and microbial community composition of a biofilm hydrolytic-aerobic recycling process treating anthraquinone reactive dyes.

Synthetic dyes are extensively used and rarely degraded. Microbial decomposition is a cost-effective alternative to chemical and physical degradation processes. In this study, the decomposition of simulated anthraquinone reactive dye (Reactive Blue 19; RB19) at a concentration of 400-mg/L in wastewater by a biofilm hydrolytic-aerobic recycling system was investigated over a range of recycling fluxes. The 16S rDNA-based fingerprint technique was also used to investigate the microbial community composition. Results indicated that the recycling flux was a key factor that influenced RB19 degradation. The RB19 and COD removal efficiency could reach values as high as 82.1% and 95.4%, respectively, with a recycling flux of 10 mL/min. Molecular analysis indicated that some strains were similar to Aeromonadales, Tolumonas, and some uncultured clones were assumed to be potential decolorization bacteria. However, the microbial community composition in the reactors remained relatively stable at different recycling fluxes. This study provided insights on the decolorization capability and the population dynamics during the decolorization process of anthraquinone dye wastewater.

Role of MnO2 in controlling iron and arsenic mobilization from illuminated flooded arsenic-enriched soils.

This study examined the role of intermittent illumination/dark conditions coupled with MnO2-ammendments to regulate the mobility of As and Fe in flooded arsenic-enriched soils. Addition of MnO2 particles with intermittent illumination led to a pronounced increase in the reductive-dissolution of Fe(III) and As(V) from flooded soils compared to a corresponding dark treatments. A higher MnO2 dosage (0.10 vs 0.02 g) demonstrated a greater effect. Over a 49-day incubation, maximum Fe concentrations mobilized from the flooded soils amended with 0.10 and 0.02 g MnO2 particles were 2.39 and 1.85-fold higher than for non-amended soils under dark conditions. The corresponding maximum amounts of mobilized As were at least 92 % and 65 % higher than for non-amended soils under dark conditions, respectively. Scavenging of excited holes by soil humic/fulvic compounds increased mineral photoelectron production and boosted Fe(III)/As(V) reduction in MnO2-amended, illuminated soils. Additionally, MnO2 amendments shifted soil microbial community structure by enriching metal-reducing bacteria (e.g., Anaeromyxobacter, Bacillus and Geobacter) and increasing c-type cytochrome production. This microbial diversity response to MnO2 amendment facilitated direct contact extracellular electron transfer processes, which further enhanced Fe/As reduction. Subsequently, the mobility of released Fe(II) and As(III) was partially attenuated by adsorption, oxidation, complexation and/or coprecipitation on active sites generated on MnO2 surfaces during MnO2 dissolution. These results illustrated the impact of a semiconducting MnO2 mineral in regulating the biogeochemical cycles of As/Fe in soil and demonstrated the potential for MnO2-based bioremediation strategies for arsenic-polluted soils.

Cadmium sulfide nanoparticles-assisted intimate coupling of microbial and photoelectrochemical processes: Mechanisms and environmental applications.

Intimate coupling of microbial extracellular electron transfer (EET) and photoelectrochemical processes is an emerging research area with great potential to circumvent many disadvantages associated with traditional techniques that depend on independent microbial or photocatalysis treatment. Microbial EET processes involve microorganism oxidation of extracellular electron donors for respiration and synchronous reduction of extracellular electron acceptors to form an integrated respiratory chain. Coupled microbial EET-photoelectrochemical technologies greatly improve energy conversion efficiency providing both economic and environmental benefits. Among substitutes for semiconductor photocatalysts, cadmium sulfide nanoparticles (CdS NPs) possess several attractive properties. Specifically, CdS NPs have suitable electrical conductivity, large specific surface area, visible light-driven photocatalysis capability and robust biocompatibility, enabling them to promote hybrid microbial-photoelectrochemical processes. This review highlights recent advances in intimately coupled CdS NPs-microbial extracellular electron transfer systems and examines the mechanistic pathways involved in photoelectrochemical transformations. Finally, the prospects for emerging applications utilizing hybrid CdS NPs-based microbial-photoelectrochemical technologies are assessed. As such, this review provides a rigorous fundamental analysis of electron transport dynamics for hybrid CdS NPs-microbial photoelectrochemical processes and explores the applicability of engineered CdS NPs-biohybrids for future applications, such as in environmental remediation and clean-energy production.

Dual roles of AQDS as electron shuttles for microbes and dissolved organic matter involved in arsenic and iron mobilization in the arsenic-rich sediment.

Microbially-mediated arsenic (As) metabolism and iron (Fe) bioreduction from sediments play crucial roles in global As/Fe cycle, and their mobilization is associated with the various effects within the alliance of "mediator-bacteria-DOM (Dissolved Organic Matter)". The gradient levels (0.05, 0.10 and 1.00mM) of sodium anthraquinone-2,6-disulphonate (AQDS) as a mediator were investigated for their impact on reductive dissolution of As(V) and Fe(III) from arsenic-rich sediment. For the overall performance of AQDS-mediated reductive dissolution on As(V) and Fe(III), a more positive effect resulting from 0.05mM AQDS was observed compared to 0.10mM, whereas an inhibitory effect was observed with 1.00mM. Compared to the biotic supplementation with acetate as electron donors, approximately 13- and 6-fold increased levels of As(III) were released with 0.05 and 0.10mM, respectively, compared to 1.00mM AQDS (107.51µg/L), and approximately 4- and 3-fold increased Fe(II) levels (40.72mg/L) were observed during the same conditions. Multiple-dynamic effects of "bacteria-AQDS-DOM", which result from AQDS, shifted the microbial community and synchronously derived terrestrial DOM, which potentially changes the DOM substrate and complex formation of As(III)-Fe(II)-humic DOM. High-throughput sequencing results indicated an increase in the abundance of metal-reducing bacteria (e.g., Bacillus (>16%), Lactococcus (>13%), Pseudomonas (>4%) and Geobacter (>3%)) when supplemented with 0.05 and 0.10mM of AQDS. However, a boost increasing the abundance of metal oxidizing bacteria was observed with Alicyclobacillus (>16%), Burkholderia (>7%), and Bradyrhizobium (>5%) upon supplementation with 1.00mM AQDS. These novel insights have profound environmental implications and significance in terms of engineering, not only for understanding the cycle of As/Fe in sediment biochemical processes but for considering future alternative bioremediation treatments.