Impact of iron reduction on the metabolism of Clostridium acetobutylicum

Azo dye anaerobic treatment in anaerobic reactors coupled with PVA/Fe/Starch gel bead

A novel bio-carrier, PVA/Fe/starch gel bead, was fabricated and developed to enhance the anaerobic treatment performance of synthetic azo dye-containing wastewater. PVA-gel beads with 5 % magnetite and 0.5 % starch were optimal for physical strength and treatment performance. A pair of 2 L-up-flow anaerobic sludge blankets (UASB), one with the bead (UB) and another without (U) as a controller, operated continuously at 30 °C and an HRT of 11-24 h for 302 days. UB showed better performance than U in most phases, especially with influent dye of 200 mg·L-1, suggesting a greater tolerance to dye toxicity of UB than U. Microbial analysis revealed that the PVA/Fe/starch gel beads successfully captured the dye degrader Clostridium. Diversity indices indicated that PVA/Fe/Starch gel beads effectively support microbial diversity and resilience under varying dye concentrations. Overall, these findings demonstrate the potential of PVA/Fe/Starch gel beads to improve the stability and efficiency of the dye treatment system.

Variable effects of soil organic matter on arsenic behavior in the vadose zone under different bulk densities

The nonstationary nature of water and oxygen content in the vadose zone determines various biogeochemical reactions regarding arsenic (As) therein, which affects the groundwater vulnerability to As contamination at a site. In the present study, we evaluated the effect of soil organic matter (OM) on the behavior of As using specifically designed soil columns that simulated the vadose zone. Three wet-dry cycles were applied to each of the four columns with different OM contents and bulk densities. OM was found to exhibit variable effects, either inhibiting or accelerating the mobilization of As, depending on bulk density. At a moderate bulk density (< 1.27 g/cm³), OM slightly lowered the pH of pore water, which enhanced the sorption of As onto the iron (Fe) oxides, promoting the retention of As in soil. In the soil column with a relatively higher bulk density (1.36 g/cm³), however, the dissimilatory reduction of iron oxides was triggered by rich OM under oxygen-limited conditions. X-ray absorption spectroscopy analysis revealed that alternate wetting and drying transformed the Fe oxides in the soil by reductive dissolution and subsequent re-precipitation. Consequently, As was not stably retained in the soil, and its mobilization downwards was further accelerated.

Efficient isopropanol-butanol-ethanol (IBE) fermentation by a gene-modified solventogenic Clostridium species under the co-utilization of Fe(III) and butyrate

To elevate the efficiency of acetone-butanol-ethanol (ABE) fermentation by the wild-type strain WK, an optimal co-utilization system (20 mM Fe³⁺ and 5 g/L butyrate) was established to bring about a 22.22% increment in the yield of ABE mixtures with a significantly enhanced productivity (0.32 g/L/h). With the heterologous introduction of the secondary alcohol dehydrogenase encoded gene (adh), more than 95% of acetone was eliminated to convert 4.5 g/L isopropanol with corresponding increased butanol and ethanol production by 21.08% and 65.45% in the modified strain WK::adh. Under the optimal condition, strain WK::adh was capable of producing a total of 25.46 g/L IBE biosolvents with an enhanced productivity of 0.35 g/L/h by 45.83% over the original conditions. This work for the first time successfully established a synergetic system of co-utilizing Fe(III) and butyrate to demonstrate a feasible and efficient manner for generating the value-added biofuels through the metabolically engineered solventogenic clostridial strain.

Role of indigenous microorganisms and organics in the release of iron and trace elements from sediments impacted by iron mine tailings from failed Fundão dam

After Fundão Dam failure in 2015, most of Gualaxo do Norte River in Doce River Basin in Brazil became silted by iron mining tailings consisting mainly of fine-grained quartz, hematite, and goethite. Previous work pointed to the possibility of reductive dissolution of iron and manganese from tailings, leading to mobilization of iron, manganese and trace elements. Several microorganisms were shown to reduce Fe(III) to Fe(II) and Mn(III, IV) to Mn(II) "in vitro", but their roles in mobilization of Fe and trace elements from freshwater sediments are poorly understood. In this work, bottom sediments and water collected in Gualaxo do Norte River were used to build anoxic microcosms amended with acetate, glucose or yeast extract, in order to access if heterotrophic microorganisms, either fermenters or dissimilatory Fe reducers, could reduce Fe(III) from minerals in the sediments to soluble Fe(II), releasing trace elements. The Fe(II) concentrations were measured over time, and trace elements concentrations were evaluated at the end of the experiment. In addition, minerals and biopolymers in bottom sediments were quantified. Results showed that organic substrates, notably glucose, fuelled microbial reduction of iron minerals and release of Fe(II), Mn, Ba, Al and/or Zn from sediments. In general, higher concentrations of organic substrates elicited mobilization of larger amounts of Fe(II) and trace elements from sediments. The results point to the possibility of mobilization of huge amounts of iron and trace elements from sediments to water if excess biodegradable organic matter is released in rivers affected by iron mine tailings.

Renewable biohydrogen production from Clostridium sp. LQ25 using different forms of ferric as electron acceptor

Clostridium sp. LQ25 was cultured in different forms of ferric (ferric citrate and ferric hydroxide) as electron acceptors to investigate growth, ferric reduction, hydrogen production, fermentation products and fermentation process. The growth of the strain LQ25 detected by protein was 82.8 ± 2.1 mg/L and 73.5 ± 1.7 mg/L using ferric citrate and ferric hydroxide as electron acceptors, which was 33.3 % and 18.4 % higher than without ferric, respectively. The accumulation concentration of Fe(II) was 9.0 ± 0.6 mg/L and 5.0 ± 0.2 mg/L when using ferric citrate and ferric hydroxide as electron acceptors, and ferric citrate was 1.8-fold higher than ferric hydroxide, which indicated that the ability of ferric reduction was higher using ferric citrate as electron acceptor. The hydrogen production of strain LQ25 was 238.0 ± 1.0 mmol/mol glucose and 113.0 ± 1.3 mmol/mol glucose under condition of ferric citrate and ferric hydroxide as electron acceptors, which was 2.6 and 1.2-fold higher than without ferric, respectively. The growth and hydrogen production of strain LQ25 was promoted by using ferric as electron acceptor, while the fermentation type of strain did not change and was always butyrate type. The differential expression of the genes of strain LQ25 was significant when using ferric as electron acceptor, mainly in NADH and PFL pathway. This study provided preliminary evidence for hydrogen production by Clostridium sp. LQ25 in the presence of electron acceptor.

Carbonate Minerals and Dissimilatory Iron-Reducing Organisms Trigger Synergistic Abiotic and Biotic Chain Reactions under Elevated CO2 Concentration

Increasing CO₂ emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO₂ have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, Orenia metallireducens, was cultured under 18 conditions that systematically varied in headspace CO₂ concentrations, ferric oxide loading, and dolomite (CaMg(CO₃)₂) availability. The results showed that abiotic and biotic processes interactively mediate CO₂ acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO₂ stress on microbial activity, possibly via pH control that transforms the inhibitory CO₂ to the more benign bicarbonate species. The microbial iron reduction further impacted pH via the competition between proton (H⁺) consumption during iron reduction and H⁺ generation from oxidization of the organic substrate. Under Fe(III)-rich conditions, microbial iron reduction increased pH, driving dissolved CO₂ to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO₃) under elevated CO₂, supporting its incorporation into solids. The results of these CO₂-microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO₂ acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO₂ sequestration, and modeling of carbon flux).

Structure and core taxa of bacterial communities involved in extracellular electron transfer in paddy soils across China

Microbial communities with extracellular electron transfer (EET) activity are capable of driving geochemical changes and cycles, but a comprehensive understanding of the key microbiota responsible for EET in complex soil matrices is still lacking. Herein, the EET activities, in terms of maximum current density (j_max) and accumulated charge output (C_out), of 41 paddy soils across China were evaluated from the exoelectrogenic properties with a conventional bioelectrochemical system (BES). The j_max with a range of 8.85 × 10^-4 to 0.41 A/m² and C_out with a range of 0.27 to 172.21C were obtained from these soil-based BESs. The bacterial community analyses revealed that the most abundant phylum, order, and genus were Firmicutes, Clostridiales, and Clostridum-sensus-stricto 10, respectively. Bacterial network analysis displayed the positive correlations between the majority of electroactive bacteria-containing genera and multiple other genera, indicating their underlying cooperation for the EET. Partial least squares regression (PLSR) model showed remarkable performance in describing the EET activity with 75 most abundant genera as input variables, identified that 32 genera were very important for governing the EET activities. Multiple linear regression (MLR) analyses further prioritized that the genera norank-c-Berkelbacteria and Fonticella were the key contributors, while the genus Paenibacillus was the key competitor against bacterial exoelectrogenesis in paddy soils. Moreover, the spearman analysis showed that the abundance of these keystone taxa was mainly influenced by the carbon content and pH. This approach provides a promising avenue to monitor the microbial activities in paddy soils as well as the links between microbial community composition and ecological function.

Effect of Photoreduction of Semiconducting Iron Mineral-Goethite on Microbial Community in the Marine Euphotic Zone

Marine euphotic zone is the pivotal region for interplay of light-mineral-microorganism and elements cycle, in which semiconducting minerals exist widely and iron-bearing goethite is a typical and widespread one. In this work, we have conducted in-depth researches on the effect of ferrous [Fe(II)] ions dissolved by photoreduction of goethite on microbial community structure and diversity. The mineral phase, structure and morphology of synthesized goethite were characterized by Raman, X-ray diffraction (XRD), energy disperse spectroscopy (EDS), environmental scanning electron microscope (ESEM), and atomic force microscope (AFM). Photoelectrochemical measurements tested photoelectric response and redox activity of goethite, having proved its significant property of photoelectric response with 44.11% increment of the average photocurrent density relative to the dark current density. The photoreduction experiments of goethite were conducted under light condition in simulated seawater. It has suggested the photoreduction of goethite could occur and Fe(III) was reduced to Fe(II). The dissolved Fe(II) from the photoreduction of goethite under light condition was nearly 11 times than that group without light after a 10-day reaction. Furthermore, results of microbial community sequencing analysis indicated that dissolved Fe(II) could affect the structure and regulate the decrease of microbial community diversity. The emergence of dominant bacteria associated with iron oxidation and transport protein has suggested their obvious selectivity and adaptability in the environment with adding dissolved Fe(II). This work revealed the photoreduction process of semiconducting goethite was remarkable, giving rise to a non-negligible dissolved Fe(II) and its selective effect on the structure, diversity, as well as the function of microbial community. This light-induced interaction between minerals and microorganisms may also further regulate correlative metabolic pathways of carbon cycle in the marine euphotic zone.

Direct and Indirect Reduction of Cr(VI) by Fermentative Fe(III)-Reducing Cellulomonas sp. Strain Cellu-2a

Hexavalent chromium (Cr(VI)) is recognized to be carcinogenic and toxic and registered as a contaminant in many drinking water regulations. It occurs naturally and is also produced by industrial processes. The reduction of Cr(VI) to Cr(III) has been a central topic for chromium remediation since Cr(III) is less toxic and less mobile. In this study, fermentative Fe(III)-reducing bacterial strains (Cellu-2a, Cellu-5a, and Cellu-5b) were isolated from a groundwater sample and were phylogenetically related to species of Cellulomonas by 16S rRNA gene analysis. One selected strain, Cellu-2a showed its capacity of reduction of both soluble iron (ferric citrate) and solid iron (hydrous ferric oxide, HFO), as well as aqueous Cr(VI). The strain Cellu-2a was able to reduce 15 μM Cr(VI) directly with glucose or sucrose as a sole carbon source under the anaerobic condition and indirectly with one of the substrates and HFO in the same incubations. The heterogeneous reduction of Cr(VI) by the surface-associated reduced iron from HFO by Cellu-2a likely assisted the Cr(VI) reduction. Fermentative features such as large-scale cell growth may impose advantages on the application of bacterial Cr(VI) reduction over anaerobic respiratory reduction.

Impact of organic acids and sulfate on the biogeochemical properties of soil from urban subsurface environments

Urban subsurface environments are often different from undisturbed subsurface environments due to the impacts of human activities. For example, deterioration of underground infrastructure can introduce elevated levels of Ca, Fe, and heavy metals into subsurface soils and groundwater. Likewise, leakage from sewer systems can lead to contamination by organic C, N, S, and P. However, the impact of these organic and inorganic compounds on biogeochemical processes including microbial redox reactions, mineral transformations, and microbial community transitions in urban subsurface environments is poorly understood. Here we conducted a microcosm experiment with soil samples from an urban construction site to investigate the possible biotic and abiotic processes impacted when sulfate and acetate or lactate were introduced into an urban subsurface environment. In the top-layer soil (0-0.3 m) microcosms, which were highly alkaline (pH > 10), the major impact was on abiotic processes such as secondary mineral precipitation. In the mid-layer (2-3 m) soil microcosms, the rate of Fe(III)-reduction and the amount of Fe(II) produced were greatly impacted by the specific organic acid added, and sulfate-reduction was not observed until after Fe(III)-reduction was complete. Near the end of the incubation, some genera related to syntrophic acetate oxidation and methanogenesis were observed in the lactate-amended microcosms. In the bottom-layer (7-8 m) soil microcosms, the rate of Fe(III)-reduction and the amount of Fe(II) produced were affected by the concentration of amended sulfate. Sulfate-reduction was concurrent with Fe(III)-reduction, suggesting that Fe(II) production was likely due to abiotic reduction of Fe(III) by sulfide produced by microbial sulfate reduction. The slightly acidic initial pH (~5.8) of the mid-soil system was a major factor controlling sequential microbial Fe(III) and sulfate reduction versus parallel Fe(III) and sulfate reduction in the bottom soil system, which had a neutral initial pH (~7.2). 16S rRNA gene-based community analysis revealed a variety of indigenous microbial groups including alkaliphiles, dissimilatory iron and sulfate reducers, syntrophes, and methanogens tightly coupled with, and impacted by, these complex abiotic and biogeochemical processes occurring in urban subsurface environments.

Hydrologic Alteration and Enhanced Microbial Reductive Dissolution of Fe(III) (hydr)oxides Under Flow Conditions in Fe(III)-Rich Rocks: Contribution to Cave-Forming Processes

Previous work demonstrated that microbial Fe(III)-reduction contributes to void formation, and potentially cave formation within Fe(III)-rich rocks, such as banded iron formation (BIF), iron ore and canga (a surficial duricrust), based on field observations and static batch cultures. Microbiological Fe(III) reduction is often limited when biogenic Fe(II) passivates further Fe(III) reduction, although subsurface groundwater flow and the export of biogenic Fe(II) could alleviate this passivation process, and thus accelerate cave formation. Given that static batch cultures are unlikely to reflect the dynamics of groundwater flow conditions in situ, we carried out comparative batch and column experiments to extend our understanding of the mass transport of iron and other solutes under flow conditions, and its effect on community structure dynamics and Fe(III)-reduction. A solution with chemistry approximating cave-associated porewater was amended with 5.0 mM lactate as a carbon source and added to columns packed with canga and inoculated with an assemblage of microorganisms associated with the interior of cave walls. Under anaerobic conditions, microbial Fe(III) reduction was enhanced in flow-through column incubations, compared to static batch incubations. During incubation, the microbial community profile in both batch culture and columns shifted from a Proteobacterial dominance to the Firmicutes, including Clostridiaceae, Peptococcaceae, and Veillonellaceae, the latter of which has not previously been shown to reduce Fe(III). The bacterial Fe(III) reduction altered the advective properties of canga-packed columns and enhanced permeability. Our results demonstrate that removing inhibitory Fe(II) via mimicking hydrologic flow of groundwater increases reduction rates and overall Fe-oxide dissolution, which in turn alters the hydrology of the Fe(III)-rich rocks. Our results also suggest that reductive weathering of Fe(III)-rich rocks such as canga, BIF, and iron ores may be more substantial than previously understood.

Sporulation in solventogenic and acetogenic clostridia

The Clostridium genus harbors compelling organisms for biotechnological production processes; while acetogenic clostridia can fix C1-compounds to produce acetate and ethanol, solventogenic clostridia can utilize a wide range of carbon sources to produce commercially valuable carboxylic acids, alcohols, and ketones by fermentation. Despite their potential, the conversion by these bacteria of carbohydrates or C1 compounds to alcohols is not cost-effective enough to result in economically viable processes. Engineering solventogenic clostridia by impairing sporulation is one of the investigated approaches to improve solvent productivity. Sporulation is a cell differentiation process triggered in bacteria in response to exposure to environmental stressors. The generated spores are metabolically inactive but resistant to harsh conditions (UV, chemicals, heat, oxygen). In Firmicutes, sporulation has been mainly studied in bacilli and pathogenic clostridia, and our knowledge of sporulation in solvent-producing or acetogenic clostridia is limited. Still, sporulation is an integral part of the cellular physiology of clostridia; thus, understanding the regulation of sporulation and its connection to solvent production may give clues to improve the performance of solventogenic clostridia. This review aims to provide an overview of the triggers, characteristics, and regulatory mechanism of sporulation in solventogenic clostridia. Those are further compared to the current knowledge on sporulation in the industrially relevant acetogenic clostridia. Finally, the potential applications of spores for process improvement are discussed.Key Points• The regulatory network governing sporulation initiation varies in solventogenic clostridia.• Media composition and cell density are the main triggers of sporulation.• Spores can be used to improve the fermentation process.

In Vivo Bioavailability of Selenium in Selenium-Enriched Streptococcus thermophilus and Enterococcus faecium in CD IGS Rats

The selenium (Se) enrichment of yeasts and lactic acid bacteria (LAB) has recently emerged as a novel concept; the individual health effects of these beneficial microorganisms are combined by supplying the essential micronutrient Se in a more bioavailable and less toxic form. This study investigated the bioavailability of Se in the strains Enterococcus faecium CCDM 922A (EF) and Streptococcus thermophilus CCDM 144 (ST) and their respective Se-enriched forms, SeEF and SeST, in a CD (SD-Sprague Dawley) IGS rat model. Se-enriched LAB administration resulted in higher Se concentrations in the liver and kidneys of rats, where selenocystine was the prevalent Se species. The administration of both Se-enriched strains improved the antioxidant status of the animals. The effect of the diet was more pronounced in the heart tissue, where a lower glutathione reductase content was observed, irrespective of the Se fortification in LAB. Interestingly, rats fed diets with EF and SeEF had higher glutathione reductase activity. Reduced concentrations of serum malondialdehyde were noted following Se supplementation. Diets containing Se-enriched strains showed no macroscopic effects on the liver, kidneys, heart, and brain and had no apparent influence on the basic parameters of the lipid metabolism. Both the strains tested herein showed potential for further applications as promising sources of organically bound Se and Se nanoparticles.

Reductive Transformation of Fe(III) (oxyhydr)Oxides by Mesophilic Homoacetogens in the Genus Sporomusa

Microbial reduction of iron contributes to the dissolution and transformation of iron-containing minerals in nature. Diverse groups of homoacetogenic bacteria (homoacetogens) have been reported to reduce insoluble Fe(III) oxides, such as hydrous ferric oxide (HFO), an Fe(III) mineral commonly found in soils and sediments. Several members of genus Sporomusa reportedly oxidize Fe(0), indicating the presence of an extracellular electron-uptake mechanism. However, the ability of the genus to reduce insoluble Fe(III) oxides is limited, and the underlying reduction mechanism remains to be elucidated. In this study, the HFO reduction ability of three Sporomusa spp. (Sporomusa sp. strain GT1, Sporomusa sphaeroides, and Sporomusa ovata) and a homoacetogen of a different genus (Acetobacterium woodii) were assayed under organotrophic (ethanol) and lithotrophic (H₂ + CO₂) conditions without a chelator or reducing reagent. All tested homoacetogens showed acetogenic growth and concomitant reduction of HFO under both organotrophic and lithotrophic conditions. Analysis of the growth stoichiometry showed that Fe(III) reduction does not support direct energy conservation, thereby indicating that Fe(III) reduction is a side reaction of acetogenesis to dissipate the excess reducing power. HFO was reduced to a soluble Fe(II) form by microbial activity. In addition, we observed that strain GT1, S. sphaeroides, and S. ovata reduced crystalline Fe(III) oxides, and HFO was reductively transformed into magnetite (Fe₃O₄) under phosphate-limiting conditions. Separation of HFO by a dialysis membrane still permitted Fe(II) production, although the reduction rate was decreased, suggesting that Fe(III) reduction is at least partially mediated by soluble redox compound(s) secreted from the cells. Finally, culture experiments and comparative genomic analysis suggested that electron transfer by flavins and multiheme c-type cytochrome were not directly correlated with Fe(III) reduction activity. This study reveals the capability of Sporomusa spp. in the reductive transformation of iron mineral and indicates the potential involvement of these organisms in iron and other mineral cycles in nature.

A Review of Methods to Determine Viability, Vitality, and Metabolic Rates in Microbiology

Viability and metabolic assays are commonly used as proxies to assess the overall metabolism of microorganisms. The variety of these assays combined with little information provided by some assay kits or online protocols often leads to mistakes or poor interpretation of the results. In addition, the use of some of these assays is restricted to simple systems (mostly pure cultures), and care must be taken in their application to environmental samples. In this review, the necessary data are compiled to understand the reactions or measurements performed in many of the assays commonly used in various aspects of microbiology. Also, their relationships to each other, as metabolism links many of these assays, resulting in correlations between measured values and parameters, are discussed. Finally, the limitations of these assays are discussed.

A Hybrid Extracellular Electron Transfer Pathway Enhances the Survival of Vibrio natriegens

Vibrio natriegens is the fastest-growing microorganism discovered to date, making it a useful model for biotechnology and basic research. While it is recognized for its rapid aerobic metabolism, less is known about anaerobic adaptations in V. natriegens or how the organism survives when oxygen is limited. Here, we describe and characterize extracellular electron transfer (EET) in V. natriegens, a metabolism that requires movement of electrons across protective cellular barriers to reach the extracellular space. V. natriegens performs extracellular electron transfer under fermentative conditions with gluconate, glucosamine, and pyruvate. We characterized a pathway in V. natriegens that requires CymA, PdsA, and MtrCAB for Fe(III) citrate and Fe(III) oxide reduction, which represents a hybrid of strategies previously discovered in Shewanella and Aeromonas Expression of these V. natriegens genes functionally complemented Shewanella oneidensis mutants. Phylogenetic analysis of the inner membrane quinol dehydrogenases CymA and NapC in gammaproteobacteria suggests that CymA from Shewanella diverged from Vibrionaceae CymA and NapC. Analysis of sequenced Vibrionaceae revealed that the genetic potential to perform EET is conserved in some members of the Harveyi and Vulnificus clades but is more variable in other clades. We provide evidence that EET enhances anaerobic survival of V. natriegens, which may be the primary physiological function for EET in Vibrionaceae IMPORTANCE Bacteria from the genus Vibrio occupy a variety of marine and brackish niches with fluctuating nutrient and energy sources. When oxygen is limited, fermentation or alternative respiration pathways must be used to conserve energy. In sedimentary environments, insoluble oxide minerals (primarily iron and manganese) are able to serve as electron acceptors for anaerobic respiration by microorganisms capable of extracellular electron transfer, a metabolism that enables the use of these insoluble substrates. Here, we identify the mechanism for extracellular electron transfer in Vibrio natriegens, which uses a combination of strategies previously identified in Shewanella and Aeromonas We show that extracellular electron transfer enhanced survival of V. natriegens under fermentative conditions, which may be a generalized strategy among Vibrio spp. predicted to have this metabolism.

Transcriptomic and Phenotypic Analysis of a spoIIE Mutant in Clostridium beijerinckii

SpoIIE is a phosphatase involved in the activation of the first sigma factor of the forespore, σ F , during sporulation. A ΔspoIIE mutant of Clostridium beijerinckii NCIMB 8052, previously generated by CRISPR-Cas9, did not sporulate but still produced granulose and solvents. Microscopy analysis also showed that the cells of the ΔspoIIE mutant are elongated with the presence of multiple septa. This observation suggests that in C. beijerinckii, SpoIIE is necessary for the completion of the sporulation process, as seen in Bacillus and Clostridium acetobutylicum. Moreover, when grown in reactors, the spoIIE mutant produced higher levels of solvents than the wild type strain. The impact of the spoIIE inactivation on gene transcription was assessed by comparative transcriptome analysis at three time points (4 h, 11 h and 23 h). Approximately 5% of the genes were differentially expressed in the mutant compared to the wild type strain at all time points. Out of those only 12% were known sporulation genes. As expected, the genes belonging to the regulon of the sporulation specific transcription factors (σ F , σ E , σ G , σ K ) were strongly down-regulated in the mutant. Inactivation of spoIIE also caused differential expression of genes involved in various cell processes at each time point. Moreover, at 23 h, genes involved in butanol formation and tolerance, as well as in cell motility, were up-regulated in the mutant. In contrast, several genes involved in cell wall composition, oxidative stress and amino acid transport were down-regulated. These results indicate an intricate interdependence of sporulation and stationary phase cellular events in C. beijerinckii.

Extracellular electron transfer in fermentative bacterium Anoxybacter fermentans DY22613T isolated from deep-sea hydrothermal sulfides

Dissimilatory Fe(III)-reducing bacteria (DIRBs) could reduce extracellular Fe(III) to Fe(II) via extracellular electron transfer (EET), playing an important role in biogeochemical cycling of Fe(III). Previous studies have noted the key role of multi-heme c-type cytochromes (MHCs) involved in EET by respiratory-type DIRBs, and proposed indirect electron transfer through the use of redox electron shuttles (e.g., flavins) or Fe(III)-chelation. However, knowledge about the EET of fermentative DIRBs was vitally scarce. Here, Anoxybacter fermentans DY22613^T is a typical fermentative DIRB isolated from deep-sea hydrothermal sulfides, and it could utilize soluble Fe(III)-citrate and solid Fe(III)-bearing minerals as extracellular electron acceptors. Unlike respiratory-type DIRBs that utilize MHCs, this strain lacked MHCs to mediate EET. Besides, it did not adopt Fe(III)-chelation to mediate indirect EET. Nonetheless, genes encoding biosynthesis pathway of redox molecules (e.g., flavins) were found in its genome and their gene expression was up-regulated with Fe(III) reduction, suggesting redox molecules may mediate indirect EET by this strain. Subsequent physiological and biochemical tests further demonstrated endogenous riboflavin acted as main electron shuttles to mediate indirect EET by this strain, and menaquinone, indole played an assistant role in this process. Besides, this strain could employ exogenous humic acids to facilitate indirect EET. The mode of exogenous and endogenous redox molecules to co-mediate indirect EET by fermentative A. fermentans DY22613^T, expands our knowledge about EET of fermentative DIRBs, and would contribute to better understand its ecological role in the biogeochemistry cycle of iron.

A novel green approach for fabricating visible, light sensitive nano-broccoli-like antimony trisulfide by marine Sb(v)-reducing bacteria: Revealing potential self-purification in coastal zones

Antimony trisulfide (Sb₂S₃) is industrially important for processes ranging from a semiconductor dopant through batteries to a flame retardant. Approaches for fabricating Sb₂S₃ nanostructures or thin films are by chemical or physicochemical methods, while there have been no report focused on the biological synthesis of nano Sb₂S₃. In the present study, we fabricated nano-broccoli-like Sb₂S₃ using Sb(V) reducing bacteria. Thirty four marine and terrestrial strains are capable of fabricating Sb₂S₃ after 1-5 days of incubation in different selective media. The nano-broccoli-like bio-Sb₂S₃ was light sensitive between 400-550 nm, acting as a photo-catalyst with the bandgap energy of 1.84 eV. Moreover, kinetic and mechanism studies demonstrated that a k value of ∼0.27 h^-1 with an R² = 0.99. The bio-Sb₂S₃ supplemented system exhibited approximately 18.4 times higher photocatalytic activity for degrading methyl orange (MO) to SO₄^2-, CO₂ and H₂O compared with that of control system, which had a k value of ∼0.015 h^-1 (R² = 0.99) under visible light. Bacterial community shift analyses showed that the addition of S or Fe species to the media significantly changed the bacterial communities driven by antimony stress. From this work it appears Clostridia, Bacilli and Gammaproteobacteria from marine sediment are potentially ideal candidates for fabricating bio-Sb₂S₃ due to their excellent electron transfer capability. Based on the above results, we propose a potential visible light bacterially catalyzed self-purification of both heavy metal and persistent organic contamination polluted coastal waters.

Identification of parameters needed for optimal anaerobic co-digestion of chicken manure and corn stover

While studies have shown that anaerobic co-digestion of chicken manure (CM) and corn stover (CS) is an efficient method to treat these agricultural wastes, the microbial ecology of these systems and optimal parameters for the digestion process are yet to be determined. In this study, the effects of different initial substrate concentrations and CS : CM mixture ratios on co-digestion and microbial community structure were evaluated. Results demonstrated that both the highest cumulative methane yields and methane production rates were obtained from reactors with a CS : CM ratio of 1 : 1 during hemi-solid-state anaerobic digestion (HSS-AD). Cumulative methane yields and methane production rates were 24.8% and 42% lower in solid-state anaerobic digestion (SS-AD) reactors using the same CS : CM ratios. Analysis of microbial community structures revealed that cellulolytic bacteria and a diversity of syntrophic microorganisms capable of direct interspecies electron transfer (DIET) and hydrogen interspecies transfer (HIT) were enriched in the best-performing reactors. Methanosarcina species also dominated during HSS-AD, and their presence was positively correlated with methane production in the reactors.