Electrochemical induction of high performance electricity generation by novel marine electroactive Rossellomorea aquimaris MT01.

Microaerophilic, phototrophic and nitrate-reducing Fe(II)-oxidizers co-exist in coastal marine and littoral freshwater sediments. However, the in situ abundance, distribution and diversity of metabolically active Fe(II)-oxidizers remained largely unexplored. Here, we characterized the microbial community composition at the oxic-anoxic interface of littoral freshwater (Lake Constance, Germany) and coastal marine sediments (Kalø Vig and Norsminde Fjord, Denmark) using DNA-/RNA-based next-generation 16S rRNA (gene) amplicon sequencing. All three physiological groups of neutrophilic Fe(II)-oxidizing bacteria were found to be active in marine and freshwater sediments, revealing up to 0.2% anoxygenic photoferrotrophs (e.g., Rhodopseudomonas, Rhodobacter, Chlorobium), 0.1% microaerophilic Fe(II)-oxidizers (e.g., Mariprofundus, Hyphomonas, Gallionella) and 0.3% nitrate-reducing Fe(II)-oxidizers (e.g., Thiobacillus, Pseudomonas, Denitromonas, Hoeflea). Active Fe(III)-reducing bacteria (e.g., Shewanella, Geobacter) were most abundant (up to 2.8%) in marine sediments and co-occurred with cable bacteria (up to 4.5%). Geochemical profiles of Fe(III), Fe(II), O2 , light, nitrate and total organic carbon revealed a redox stratification of the sediments and explained 75%-85% of the vertical distribution of microbial taxa, while active Fe-cycling bacteria were found to be decoupled from geochemical gradients. We suggest that metabolic flexibility, microniches in the sediments, or interrelationships with cable bacteria might explain the distribution patterns of active Fe-cycling bacteria.

Exploiting synergies between microbial electrochemical technologies and synthetic biology.

It's time to elucidate what are the key points to promote bio-electro-Fenton and bio-Fenton-like work efficiently: Mechanisms, enhancement strategies, and applications.

Higher plant n-alkane average chain length as an indicator of petrogenic hydrocarbon contamination in marine sediments

Mediator‐based extracellular electron transfer (EET) pathways can balance the redox metabolism of microbes. However, such electro‐biosynthesis processes are constrained by the unknown underlying EET mechanisms. In this paper, Pseudomonas putida was studied to systematically investigate its EET pathway to transition metal complexes (i. e., [Fe(CN)6]3−/4− and [Co(bpy)3]3+/2+; bpy=2,2′‐bipyridyl) under anaerobic conditions. Comparative proteomics showed the aerobic respiratory components were upregulated in a bioelectrochemical system without oxygen, suggesting their potential contribution to EET. Further tests found inhibiting cytochrome c oxidase activity by NaN3 and NADH dehydrogenase by rotenone did not significantly change the current output. However, the EET pathway was completely blocked, while cytochrome c reductase activity was inhibited by antimycin A. Although it cannot be excluded that cytochrome c and the periplasmic subunit of cytochrome c oxidase donate electrons to the transition metal complexes, these results strongly demonstrate that cytochrome c reductase is a key complex for the EET pathway.

Rapid start-up sulfur-driven autotrophic denitrification granular process: Extracellular electron transfer pathways and microbial community evolution

Nano-magnetite effects on CO2 reduction of homoacetogens with different extracellular electron transfer pathways

New insights into the anaerobic microbial degradation of decabrominated diphenyl ether (BDE-209) in coastal marine sediments

The overlap of microbiology and electrochemistry provides plenty of opportunities for a deeper understanding of the redox biogeochemical cycle of natural-abundant elements (like iron, nitrogen, and sulfur) on Earth. The electroactive microorganisms (EAMs) mediate electron flows outward the cytomembrane via diverse pathways like multiheme cytochromes, bridging an electronic connection between abiotic and biotic reactions. On an environmental level, decades of research on EAMs and the derived subject termed “electromicrobiology” provide a rich collection of multidisciplinary knowledge and establish various bioelectrochemical designs for the development of environmental biotechnology. Recent advances suggest that EAMs actually make greater differences on a larger scale, and the metabolism of microbial community and ecological interactions between microbes play a great role in bioremediation processes. In this perspective, we propose the concept of microbial electron transfer network (METN) that demonstrates the “species-to-species” interactions further and discuss several key questions ranging from cellular modification to microbiome construction. Future research directions including metabolic flux regulation and microbes–materials interactions are also highlighted to advance understanding of METN for the development of next-generation environmental biotechnology.

Inoculum source determines the stress resistance of electroactive functional taxa in biofilms: A metagenomic perspective

Promoting efficiency of microbial extracellular electron transfer by synthetic biology

Marine sediments harbor metabolically versatile bacteria whose activities can influence the cycle of nutrients on global scales. Microbial communities driving nitrogen (N) cycling are extremely diverse, thus making it difficult to identify the functional groups and elucidate controls on their activity. Denitrifiers in sediments remove significant amounts of N from the coastal ocean, while diazotrophs are typically considered inconsequential. Recently, N fixation has been shown to be a potentially important source of N in coastal sediments, however, the environmental drivers controlling this process are poorly understood. The goal of this dissertation was to identify and target the likely active denitrifiers and N fixers in coastal marine sediments through the analysis of genes expressed for proteins essential for denitrification, a nitrite reductase (nirS) and nitrogen fixation, a nitrogenase subunit (nifH). Subsequently, quantitative PCR and RT-PCR were used to follow the changes in abundance, distribution and nifH expression of the dominant diazotrophic groups in response to environmental conditions. Two groups of diazotrophs related to anaerobic sulfur/iron reducers and sulfate reducers dominated nifH expression in Narragansett Bay (RI, USA) sediments. Increased seawater temperature and severe hypoxia appear to be influencing the proliferation and activity of these two bacterial groups. Oxygen depletion also affects sediment porewater nutrients, indicating a shift in benthic microbial processes. In offshore sediments, nifH expression was related to UCYN-A, a unicellular cyanobacterium. These findings suggest that UCYN-A, a known tropical and subtropical open ocean symbiont, has a broader thermal tolerance than previously assumed and can survive in the benthos after the lifespan of its eukaryotic host. Diazotrophic activity by these microbial communities in marine sediments is an unanticipated contribution of fixed N to coastal systems. Climate change may exacerbate the environmental conditions in which these microbes become active, consequently altering the global marine nitrogen cycle in unprecedented ways.

Electroactive microorganisms (EAMs) could utilize extracellular electron transfer (EET) pathways to exchange electrons and energy with their external surroundings. Conductive cytochrome proteins and nanowires play crucial roles in controlling electron transfer rate from cytosol to extracellular electrode. Many previous studies elucidated how the c‐type cytochrome proteins and conductive nanowires are synthesized, assembled, and engineered to manipulate the EET rate, and quantified the kinetic processes of electron generation and EET. Here, we firstly overview the electron transfer pathways of EAMs and quantify the kinetic parameters that dictating intracellular electron production and EET. Secondly, we systematically review the structure, conductivity mechanisms, and engineering strategies to manipulate conductive cytochromes and nanowire in EAMs. Lastly, we outlook potential directions for future research in cytochromes and conductive nanowires for enhanced electron transfer. This article reviews the quantitative kinetics of intracellular electron production and EET, and the contribution of engineered c‐type cytochromes and conductive nanowire in enhancing the EET rate, which lay the foundation for enhancing electron transfer capacity of EAMs.

The increasing production and utilization of polycyclic aromatic hydrocarbons (PAHs) and commercial silver nanoparticles (AgNPs) have raised concerns about their potential environmental release, with coastal sediments as a substantial sink. To better understanding the effects of these contaminants on denitrification processes in coastal marine sediments, a short-term exposure simulation experiment was conducted. We investigated the effects of single and combined contamination of phenanthrene (Phe) and AgNPs on denitrification processes in a coastal marine sediment. Results showed that all contaminated treatment groups had different degrees of inhibitory effect on denitrification activity, denitrifying enzyme activity, total bacteria count and denitrifying genes. The inhibitory effect sequence of each treatment group was combined treatment > AgNPs treatment > Phe treatment. Moreover, the inhibitory effects of denitrifying genes were much larger than that of total bacteria count, indicating that the pollutants had specific toxic effects on denitrifying bacteria. The sequence of sensitivity of three reduction process to pollutants was N2O > NO2- > NO3-. All contaminated treatment groups could increase NO3-, NO2- and N2O accumulation. Furthermore, according to the linear relationship between functional gene or reductase and denitrification process, we also found that the abundance of denitrifying genes could better predict the influence of Phe and AgNPs on sediment denitrification than the denitrifying bacterial diversity. In addition, at the genus level, the community structure of nirS- and nosZ-type denitrifying bacteria changed dramatically, while changes at the phylum level were comparatively less pronounced. Single and combined contamination of Phe and AgNPs could reduce the dominance of Pseudomonas, which may lead to a potential slow-down in the degradation of Phe and inhibition of denitrification, especially the combined contamination. Overall, our study revealed that combined contamination of Phe and AgNPs could lead to an increase in NO3-, NO2- and N2O accumulation in coastal sediment, which poses a risk of eutrophication in coastal areas, exacerbates the greenhouse effect and has adverse effects on global climate change.

Sulfur is an important element in the metabolism of salt marshes and subtidal, coastal marine sediments because of its role as an electron acceptor, carrier, and donor. Sulfate is the major electron acceptor for respiration in anoxic marine sediments. Anoxic respiration becomes increasingly important in sediments as total respiration increases, and so sulfate reduction accounts for a higher percentage of total sediment respiration in sediments where total respiration is greater. Thus, sulfate accounts for 25% of total sediment respiration in nearshore sediments (200 m water depth or less) where total respiration rates are 0.1 to 0.3gCm−1 day−1 , for 50% to 70% in nearshore sediments with higher rates of total respiration (0.3 to 3gCm−2 day−1), and for 70% to 90% in salt marsh sediments where total sediment respiration rates are 2.5 to 5.5gcm−2 day−1 . During sulfate reduction, large amounts of energy from the respired organic matter are conserved in inorganic reduced sulfur compounds such as soluble sulfides, thiosulfate, elemental sulfur, iron monosulfides, and pyrite. Only a small percentage of the reduced sulfur formed during sulfate reduction is accreted in marine sediments and salt marshes. When these reduced sulfur compounds are oxidized, energy is released. Chemolithoautotrophic bacteria which catalyze these oxidations can use the energy of oxidation with efficiencies (the ratio of energy fixed in organic biomass to energy released in sulfur oxidation) of up to 21–37% to fix CO2 and produce new organic biomass. Chemolithoautotrophic bacterial production may represent a significant new formation of organic matter in some marine sediments. In some sediments, chemolithoautotrophic bacterial production may even equal or exceed organoheterotrophic bacterial production. The combined cycle of anaerobic decomposition through sulfate reduction, energy conservation as reduced sulfur compounds; and chemolithoautotrophic production of new organic carbon serves to take relatively low-quality organic matter from throughout the sediments and concentrate the energy as living biomass in a discrete zone near the sediment surface where it can be readily grazed by animals.