Fermentative Bacteria Research Articles

Reductive acetogenesis is a dominant process in the ruminant hindgut

BackgroundThe microbes residing in ruminant gastrointestinal tracts play a crucial role in converting plant biomass to volatile fatty acids, which serve as the primary energy source for ruminants. This gastrointestinal tract comprises a foregut (rumen) and hindgut (cecum and colon), which differ in structures and functions, particularly with respect to feed digestion and fermentation. While the rumen microbiome has been extensively studied, the cecal microbiome remains much less investigated and understood, especially concerning the assembling microbial communities and overriding pathways of hydrogen metabolism.ResultsTo address this gap, we comparatively investigated the composition, capabilities, and activities of the rumen and the cecum microbiome using goats as an experimental ruminant model. In situ measurements showed significantly higher levels of dissolved hydrogen and acetate in the cecum than in the rumen. Increased dissolved hydrogen indicated distinct processes and reduced coupling between fermentative H2 production and utilization, whereas higher levels of acetate could be caused by slower VFA absorption through cecal papillae than through the rumen papillae. Microbial profiling indicated that the cecum harbors a greater abundance of mucin-degrading microbes and fermentative hydrogen producers, whereas the rumen contains a higher abundance of fibrolytic fermentative bacteria, hydrogenotrophic respiratory bacteria, and methanogenic archaea. Most strikingly, reductive acetogenic bacteria were 12-fold more abundant in the cecum. Genome-resolved metagenomic analysis unveiled that the cecum acetogens are both phylogenetically and functionally distinct from those found in the rumen. Further supporting these findings, two in vitro experiments demonstrated a marked difference in hydrogen metabolism pathways between the cecum and the rumen, with increased acetate production and reduced methanogenesis in the cecum. Moreover, comparative analysis across multiple ruminant species confirmed a strong enrichment of reductive acetogens in the hindguts, suggesting a conserved functional role.ConclusionsThese findings highlight an enrichment of acetogenesis in a key region of the gastrointestinal tract and reshape our understanding of ruminant hydrogen metabolism and how the H2 can be managed in accord to livestock methane mitigation efforts.4u9SCdfN3oG9CLNNa6zYDaVideo

Capsaicin Modulates Ruminal Fermentation and Bacterial Communities in Beef Cattle with High-Grain Diet-Induced Subacute Ruminal Acidosis.

This study was developed with the goal of exploring the impact of capsaicin on ruminal fermentation and ruminal bacteria in beef cattle affected by high-grain diet-induced subacute ruminal acidosis (SARA). In total, 18 healthy Simmental crossbred cattle were randomized into three separate groups (n = 6/group): (1) control diet (CON; forage-to-concentrate ratio = 80:20); (2) high-grain diet (SARA; forage-to-concentrate ratio = 20:80); and (3) high-grain diet supplemented with capsaicin (CAP; 250 mg/cattle/day). The study was conducted over a 60-day period. The results showed that the SARA model was successfully induced in the SARA group with a high-grain diet. Relative to the SARA group, the addition of capsaicin elevated the ruminal pH from 5.40 to 6.36 (p < 0.01), and decreased the total volatile fatty acids (VFAs) from 133.95 to 82.86 mmol/L (p < 0.01), aligning closely with the levels observed in the CON group. The addition of capsaicin increased the alpha diversity of ruminal bacteria relative to the SARA group, as evidenced by a lower Simpson index (p < 0.05), together with increases in the Ace, Chao, and Shannon indices (p < 0.05). Bacteroidota and Firmicutes were the most common phyla across all treatment groups, while Prevotella was the predominant genera. The unique bacterial genera (LDA scores > 4) identified within the SARA group comprised Succinivibrionaceae_UCG-001, Succinivibrio, NK4A214_group, Lachnospiraceae_NK3A20_group, and Ruminococcus, which may serve as potential biomarkers for the diagnosis of SARA. The unique genera associated with the CON group included Rikenellaceae_RC9_gut_group, Prevotellaceae_UCG-003, and U29-B03, while those for the CAP group included Succiniclasticum and Prevotellaceae_UCG-004. In summary, these results suggest that dietary capsaicin supplementation can limit the adverse effects of SARA through the modulation of bacterial communities within the rumen, thus altering ruminal fermentation in beef cattle.

Vanadate reduction by gram-positive fermentative bacteria isolated from deep-sea sediments on the northern Central Indian Ridge.

The oxidation states of vanadium determine its mobility and toxicity, and dissimilatory vanadate reduction has been reported in several microorganisms, highlighting the potential significance of this pathway in the remediation of vanadium contamination and the biogeochemical cycle. However, to date, most known microorganisms capable of reducing vanadate are Gram-negative respiratory bacteria belonging to the phylum Proteobacteria. In this study, we isolated Tepidibacter mesophilus strain VROV1 from deep-sea sediments on the northern Central Indian Ridge and investigated its ability to reduce vanadium and the impact of vanadate on its cellular metabolism. A series of culture experiments revealed that the isolated strain efficiently reduces V(V) to V(IV) during fermentation, even at mM levels, and this reduction involves a direct biological process rather than indirect reduction via metabolic products. Vanadium affects microbial carbon and nitrogen metabolism. Notably, in the presence of vanadate, alanine production decreases, suggesting that metabolic flux is diverted from the transamination reaction to vanadate reduction. T. mesophilus VROV1 is the second Gram-positive bacterium identified to reduce vanadium, following Lactococcus raffinolactis, but these bacteria belong to different classes: T. mesophilus is classified as Clostridia, whereas L. raffinolactis is classified as Bacilli. The specific rate of vanadate removal by VROV1 was as high as 2.8 pmol/cell/day, which is comparable to that of metal-reducing bacteria and markedly exceeds that of L. raffinolactis. Our findings expand the distribution of vanadate-reducing organisms within the bacterial domain. Given the wide range of natural habitats of T. mesophilus and its close relatives, we speculate that fermentative vanadate reduction may have a greater impact on the global biogeochemical cycle of vanadium than previously thought.

Characteristics of Phages and Their Interactions With Hosts in Anaerobic Reactors.

Anaerobic digestion (AD) of organic wastes relies on the interaction and cooperation of various microorganisms. Phages are crucial components of the microbial community in AD systems, but their diversity and interactions with the prokaryotic populations are still inadequately comprehended. In this study, 2121 viral operational taxonomic units (vOTUs) were recovered from 12 anaerobic fatty acid-fed reactors. Notably, 63.1% of these vOTUs could not be assigned to any known family, revealing a substantial presence of uncharted phages specifically associated with AD environments. Over half of the vOTUs associated with hosts had the capability to infect multiple hosts, ranging from 2 to 49, with a prevalent tendency to infect 2-5 hosts. In silico predictions of phage-host linkages uncovered that only a small fraction of vOTUs were shared across different functional groups, including fermentative bacteria, syntrophic fatty acid-oxidising bacteria (SFOB) and methanogens. Phages linked to hosts in all three groups primarily consisted of generalists and temperate species, especially those linked to SFOB. Additionally, metabolic reconstruction identified auxiliary metabolic genes participating in fatty acid degradation, methanogenesis and energy conservation. The present study provides insights into phage characteristics and their insitu interactions with prokaryotic hosts, highlighting their ecological role in AD systems.

Reduction of cyanide concentration in cassava by lactic acid bacteria fermentation: A meta-analysis

Reduction of cyanide concentration in cassava by lactic acid bacteria fermentation: A meta-analysis

Mechanism study on removal of browning pigment from high temperature sterilized lotus rhizome juice by lactic acid bacteria fermentation

Mechanism study on removal of browning pigment from high temperature sterilized lotus rhizome juice by lactic acid bacteria fermentation

Bacillus safensis from Sauerkraut Alleviates Acute Lung Injury Induced by Methicillin-Resistant Staphylococcus aureus through the Regulation of M2 Macrophage Polarization via Its Metabolite Esculin.

Sauerkraut contains various fermentative microorganisms that produce active metabolites, enhancing immunity and resistance to infections. However, its effects on methicillin-resistant Staphylococcus aureus (MRSA)-induced acute lung injury (ALI) remain unclear. Using RAW264.7 cells and a mouse model, we demonstrated that Bacillus safensis SK14 (BS SK14), an understudied fermentative bacterium, has an immunomodulatory effect on MRSA-induced ALI. BS SK14 significantly reduced the inflammatory responses. Supplementation with live BS SK14 or its culture supernatant increased survival rates, reduced lung damage, and attenuated inflammation in ALI model mice. LC-MS/MS analysis identified esculin as the key metabolite responsible for these effects. BS SK14 produces esculin via the gut-lung axis, inhibiting the TLR2-MyD88-NF-κB pathway, reducing Keap1 levels, and activating the Nrf2-ARE pathway. This decreased MRSA-induced M1 polarization and increased M2 polarization, enhancing antioxidant and anti-inflammatory activities in mice. Collectively, these results reveal that BS SK14 and its metabolite esculin exert therapeutic effects on MRSA-induced ALI through a multifactorial strategy.

Isolation and characterization of cellulose-mineralizing haloalkaliphilic bacteria from Siberian soda lakes

Soda lakes are unique double-extreme habitats characterized by high salinity and soluble carbonate alkalinity, yet harboring rich prokaryotic life. Despite intensive microbiology studies, little is known about the identity of the soda lake hydrolytic bacteria responsible for the primary degradation of the biomass organic matter, in particular cellulose. In this study, aerobic and anaerobic enrichment cultures with three forms of native insoluble cellulose inoculated with sediments from five soda lakes in south-western Siberia resulted in the isolation of four cellulotrophic haloalkaliphilic bacteria and their four saccharolytic satellites. The final aerobic enrichment included a cellulotrophic bacteroidetes (strain ABcell3) related to Sporocytophaga accompanied by a hemicellulolytic Marinimicrobium strain ABcell2. The anaerobic enrichments resolved in three primary cellulotrophic bacteria and their three saccharolytic bacteroidetes satellites. The culture selected on amorphous cellulose (ac) included a new cellulotrophic member of the Chitinispirillaceae (Fibrobacterota)—strain ANBcel5, and two different saccharolytic satellites from the Marinilabiliales and Balneolales orders. The final enrichment selected on Sigma 101 cellulose consisted of an endospore-forming cellulotrophic strain ANBcel31 belonging to the genus Herbivorax (Acetivibrionales) and its saccharolytic satellite from the Balneolales order. The anaerobic enrichment on a filter paper yielded a binary consortium with the cellulotrophic endospore-forming Halanaerobiales strain ANBcel28 in obligate syntrophy with a cellobiose-utilizing Natronincola. A functional genome analysis of the cellulotrophic isolates confirmed the presence of a large repertoire of genes encoding excreted cellulases, mostly from the GH9 and GH5 families, and indicated that in the endospore-forming anaerobic strains, ANBcel28 and ANBcel31 most of their endo-glucanases are assembled in cellulosomes. Overall, this study showed that cellulose can be mineralized in soda lakes at moderately saline and highly alkaline conditions either by aerobic or fermentative haloalkaliphilic bacteria.

Optimization of Eco Enzyme Production Using Bacterial Starters and Fermentative Fungi

Eco Enzyme is a natural fermentation product made from organic waste such as leftover fruits and vegetables, which has various benefits, including serving as an environmental cleaner and pollution reducer. This research aims to optimize the production of Eco Enzyme by using specific fermentative bacterial starters to enhance fermentation efficiency and the quality of the final product. In this study, the types of fermentative bacteria used are Lactobacillus bulgaricus, Lactobacillus acidophilus, and the fungi Saccharomyces cerevisiae and Aspergillus niger. Parameters such as pH, temperature, and fermentation duration are strictly regulated and monitored to identify optimal conditions for Eco Enzyme production. The research results indicate that the use of certain fermentative bacterial starters can accelerate fermentation time by up to 30% and increase enzyme activity by 20% compared to natural fermentation processes without starters. The characteristics also show the same results, namely acidic pH, characteristic fresh aroma, fresh eco enzyme value and normal TDS (ranged 1,030 ppm - 1,700 ppm). This optimization not only produces a more efficient and high-quality Eco Enzyme product, but it can also serve as an innovative step towards more sustainable and environmentally friendly organic waste management.

Effects of Lactic Acid Bacteria Fermentation and In Vitro Simulated Digestion on the Bioactivities of Purple Sweet Potato Juice.

The effects of lactic acid bacteria fermentation and in vitro simulated digestion on phenolic bioavailability, phenolic bioavailability, and antioxidant activity of purple sweet potato juice (PSPJ) were investigated. The PSPJ was fermented by Lactobacillus rhamnosus and Streptococcus thermophilus. The viable bacterial count, phenolic components, antioxidant activity, phenolic bioaccessibility, and phenolic bioavailability of PSPJ were analyzed during the simulated digestion process in vitro. The data displayed that lactic acid bacteria fermentation increased total α-glucosidase inhibition, total flavonoid content, and ratephenolic content. The antioxidant activities were improved after in vitro simulated digestion due to the biotransformation of phenolic substances by lactic acid bacteria fermentation. The bioaccessibility and bioavailability of phenols in PSPJ were improved with fermentation of lactic acid bacteria. Furthermore, the viable bacteria count of the two strains was significantly improved (>7 log CFU/mL) after simulated digestion in vitro.

Mathematical modeling of biohydrogen production via dark fermentation of fruit peel wastes by Clostridium butyricum NE95

BackgroundBiohydrogen production from agro-industrial wastes through dark fermentation offers several advantages including eco-friendliness, sustainability, and the simplicity of the process. This study aimed to produce biohydrogen from fruit and vegetable peel wastes (FVPWs) by anaerobic fermentative bacteria isolated from domestic wastewater. Kinetic analysis of the produced biohydrogen by five isolates on a glucose medium was analyzed using a modified Gompertz model (MGM). Besides, the feasibility of hydrogen production by Clostridium butyricum NE95 using FVPWs as substrates was investigated.ResultsThe bacterial isolate NE95 was selected as the highest biohydrogen producer with maximum biohydrogen production (Hmax) of 1617.67 ± 3.84 mL/L, Rmax (MGM) of 870.77 mL/L/h and lag phase (λ) of 28.37 h. NE95 was phenotypically and genetically identified as C. butyricum and its 16 S rRNA gene sequence was deposited in the GenBank under the accession number PP581833. The genetic screening of hydrogenase gene clusters indicated the presence of Fe-Fe hydrogenase gene in C. butyricum NE95. C. butyricum NE95 showed the ability to produce biohydrogen from different FVPWs, with watermelon and melon peels being the most promising feedstocks for fermentation. It was revealed that using a mixture (1:1, w/w) of watermelon and melon peels as a substrate for C. butyricum NE95 significantly increased biohydrogen yield with Hmax of 991.00 ± 10.54 mL/L, Rmax of 236.31 mL/L/h, λ of 33.92 h and a high accuracy of R2 (0.997).ConclusionsThe study highlights the effectiveness of C. butyricum NE95 on the valorization of FVPWs and generates a sustainable source of biohydrogen production.

Whole-genome sequences of fermentative and spoilage-associated lactic acid bacteria, Lysinibacillus capsici and a Serratia marcescens isolated from commercial cucumber fermentations.

We report the annotated, whole-genome sequences of 16 bacteria isolated from commercial cucumber fermentations. The collection consists of nine fermentative and two spoilage-associated lactic acid bacteria, four Lysinibacillus strains, and a Serratia marcescens. Half the genome assemblies have fewer than 10 contigs, and the remainder have fewer than 30.

Susceptibility pattern of Ceftazidime-Avibactam against multi drug resistant gram-negative rods

This study was conducted to evaluate the susceptibility pattern of ceftazidime avibactam against multi drug resistant gram negative rods. This prospective study cross sectional study conducted in Microbiology Section of Dow Diagnostic Reference and Research Laboratory, Dow University of Health Sciences, Karachi, Pakistan. Identification of isolates was done in accordance with the standard bacteriological technique, and were distinguished based on gram staining, colony morphology and biochemical tests. Antibiotic susceptibility testing (AST) was performed on Muller-Hinton agar by Kirby-Bauer Disk Diffusion method in accordance with the Clinical Laboratory Standard Institute (CLSI) guidelines. Good sensitivity of Lactose fermenters (Escherichia coli, Klebsiella pneumoniae and Enterobacter) were observed against Ceftazidime avibactam. Pseudomonas aeruginosa exhibited 42% resistance in all clinical samples. Proteus species and Serratia have shown high resistance in our study. Our observations showed the persistence of high ceftazidime avibactam activity against pathogenic and multi drug resistant strains of Enterobacterales and Non lactose fermenting bacteria.

Study on the mechanism of lactic acid bacteria and their fermentation broth in alleviating hyperuricemia based on metabolomics and gut microbiota.

Hyperuricemia (HUA) is a metabolic disease caused by purine metabolism disorders in the body. Lactic acid bacteria (LAB) and their fermentation broth have the potential to alleviate hyperuricemia, but the potential mechanism of action is still unclear. The LAB with high inhibitory activity against xanthine oxidase (XOD) were screened out. Then the fermentation broth, fermentation supernatant and fermentation bacteria after fermentation of these LAB were administered into HUA mice, respectively. Lactobacillus reuteri NCUF203.1 and Lactobacillus brevis NCUF207.7, of which fermentation supernatant had high inhibitory activity against XOD, were screened out and administered into HUA mice. Among them, L. reuteri strain, L. reuteri fermentation broth, L. brevis fermentation broth and L. brevis fermentation supernatant could significantly reduce serum uric acid levels and inhibited the liver XOD activity in HUA mice. The GC-MS metabolomics analysis of colon contents showed that supplementation of these four substances could partially reverse the down-regulation of energy metabolism pathways such as ketone body metabolism, pyruvate metabolism and citric acid cycle in HUA mice. It could also regulate amino acid metabolism pathways such as alanine metabolism, arginine and proline metabolism, glycine and serine metabolism, and repair the disorders of amino acid metabolism caused by HUA. In addition, the intervention of L. brevis fermentation broth and L. brevis fermentation supernatant may also accelerate the catabolism of uric acid in the intestine by up-regulating the urea cycle pathway. Fecal 16S rRNA sequencing analysis showed that their intervention increased the diversity of gut microbiota in HUA mice and alleviated the gut microbiota dysregulation caused by HUA. These results indicated that the LAB and their fermentation broth may play a role in alleviating HUA by regulating intestinal metabolism and gut microbiota.

Electrochemical Detection of Carbon Steel Corrosion Induced by Fermentative Bacteria From Natural Gas Transmission Lines.

The metabolic potential and corrosive activities of a fermentative bacterial enrichment culture from a natural gas transmission line were characterised. Three metagenome-assembled genomes (MAGs) attributable to Cytobacillus, Lacrimispora and Staphylococcus spp. were obtained. These MAGs hosted genes involved in the fermentation of carbohydrates to organic acids, which was reflected in the acidification of the growth medium by the culture. To evaluate the corrosive activities of the culture, it was incubated in a split chamber-zero resistance ammetry (SC-ZRA) format. This involved deploying carbon steel coupons immersed in liquid medium in opposing chambers of an electrochemical cell. Measurement of current between the coupons indicated the extent and mechanism of corrosion. When the enrichment culture was added to one side of an SC-ZRA incubation with bicarbonate-buffered medium, pH change and corrosion were minimal. In bicarbonate-free medium, the culture acidified the medium, induced electron transfer from the uninoculated chamber to the inoculated chamber, and caused mass loss. These results indicate that fermenter-induced microbially influenced corrosion (MIC) is due to localised fluid acidification, inducing anodic reactions on the metal surface exposed to the microorganisms and mass loss of the non-exposed metal.

Lactiplantibacillus plantarum for the Preparation of Fermented Low-Bitter Enzymatic Skim Milk with Antioxidant Ability.

A high degree of hydrolysis can reduce the allergenicity of milk, while lactic acid bacteria (LAB) fermentation can further enhance the antioxidant ability of enzymatic milk. LAB with a strong antioxidant ability was screened, and the effects of LAB on the bitterness, taste and flavor of enzymatic skim milk (ESM) with a high degree of hydrolysis were investigated in this paper, in addition to the response surface methodology optimized the conditions of the LAB fermentation of ESM. The results indicate that the skim milk hydrolyzed by Protamex has a higher degree of hydrolysis and lower bitterness. The scavenging rate of 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical, the inhibition rate of hydroxyl radical (·OH) and the superoxide dismutase (SOD) activity of Lactiplantibacillus plantarum 16 and Lactococcus lactis subsp. lactis m16 are significantly higher than those of other strains (p < 0.05), while the improvement effect of L. plantarum 16 on the bitterness and flavor of ESM is better than that of L. lactis subsp. lactis m16. The fermented ESM has a strong antioxidant ability and low bitterness when the inoculum quantity of L. plantarum 16 is 5%, fermentation at 37 °C for 18 h and the pH of the ESM is 6.5, for which the DPPH free radical scavenging rate is 61.32%, the ·OH inhibition rate is 83.35%, the SOD activity rate is 14.58 and the sensory evaluation is 4.25. The contents of amino acids related to bitterness and antioxidants were reduced and increased, respectively. The ESM fermented by L. plantarum 16 has a good flavor, antioxidant ability and low bitterness.

The therapeutic effect of antioxidant postbiotic cocktail in colitis mice: A promising approach to alleviate oxidative stress in two high-fat and normal-diet feeding mice

It seems that postbiotics as a byproduct of fermentation of probiotic bacteria could be more effective in health benefits context. Therefore, in this study we aimed to assess the effectiveness of a novel postbiotic resulted from native probiotic Lactobacillus strains with robust antioxidant properties in ameliorating colitis in murine models fed with Normal-Diet or High Fat-Diet. Material and methodsEighty-eight strains of Lactobacillus and Bifidobacterium sourced from human feces and milk were screened for antioxidant activity. Six potent strains were selected to formulate a postbiotic cocktail, with its major compounds identified through gas chromatography. ResultsIn an animal study, mice with dextran sulphate sodium (DSS)-induced colitis that received the postbiotic cocktail showed significant improvements in phenotypical indices compared to the DSS group. Mice on both dietary regimens exhibited reduced adverse effects associated with DSS consumption, as indicated by lower Disease Activity Index (DAI) and Pathological Score metrics, along with increased intestinal mass and length(p<0.05). Additionally, mice receiving the postbiotic cocktail demonstrated elevated levels of antioxidant enzymes and anti-inflammatory cytokines(p<0.05). ConclusionThis suggests that the postbiotic not only mitigates inflammation but also enhances antioxidant defenses, particularly in those on a normal diet. Overall, these findings indicate that this novel postbiotic mixture has potential for effectively managing colitis, especially when combined with a healthy dietary regimen, while also highlighting opportunities to optimize environmental factors to enhance its antioxidant capabilities.

Mixed fermentation of lactic acid bacteria and sourdough on quality and storage characteristics of steamed bun

The effect of mixed fermentation with sourdough and lactic acid bacteria (Lactobacillus plantarum and Streptococcus thermophilus), the physicochemical indexes, storage characteristics of dough and bun were investigated. Compared with sourdough-only dough and bun, the mixed fermentation significantly increase the total phenol, flavonoid and hydrolyzed amino acid content of the dough, the specific volume and height-diameter ratio of mixed fermentation bun increased significantly by 18.3 % and 7.9 %, respectively (P < 0.05), along with a significant improvement in sensory quality (P < 0.05), and exhibited enhanced skin whiteness (by 2.0 %), with an increase in stomatal density and porosity by 2.6 % and 16.5 %, respectively. During a nine-day storage period, the moisture content near the skin and bun core of steamed bun decreased by 3.9 %, and 1.6 %, respectively, and the aging enthalpy values of mixed fermentation bun were significantly lower than sourdough-only bun (P < 0.05). Mixed fermentation providing a theoretical basis for the development of novel steamed bun starters.

Syntrophic relationship among microbial communities enhance methane production during temperature transition from mesophilic to thermotolerant conditions

Hydrogenotrophic methanogenesis, in a syntrophic relationship with fermentative and acetogenic bacteria, is an essential key for maximizing biogas production and reducing CO2 emissions. However, its impact on CH4 production under varying temperatures is not widely understood. This study investigates the effects of incremental temperature transition from 37 °C to 45 °C at 2 °C intervals, on anaerobic digestion (AD) using digested sewage sludge with low glucose addition. Results showed CH4 production levels of 298 and 309 ml CH4/g CODfed at 37 °C and 39 °C, respectively, and exhibited a decrease at 41 °C. A temperature increase to 43 °C restored CH4 production to 260 ml CH4/g CODfed, with lower CO2 output. At 45 °C, the CH4 - CO2 production gap widened, indicating enhanced methanogenic activity due to prolonged high temperatures. Methanothrix was the predominant methanogen, followed by Methanobacterium whose activity increased at 43 °C and 45 °C alongside the upregulation of key hydrogenotrophic pathway enzymes (fwd, ftr, mch). The increasing abundance of fermentative bacteria at 43 °C and 45 °C may upregulates hydrogenotrophic methanogenesis. Flux balance analysis revealed the role of Acetomicrobium and Clostridia sp. strains that supplied the most acetate, providing approximately 7 – 600 mmol/gDW/h to the microbial communities. These findings highlight the adaptability of microbial communities and possible syntrophic relationships in response to temperature changes, demonstrating the resilience of AD processes under varying environmental conditions.

Electroactive bacteria-established long-distance electron transfer to oxygen facilitates bio-transformation of dissolved organic matter for sediment remediation

Electroactive bacteria (EAB) in sediment commonly establish long-distance electron transfer (LDET) to access O2, facilitating the degradation of organic contaminants, which we hypothesize is mediated by the bio-transformation of dissolved organic matter (DOM). This study confirmed that EAB-established LDET to O2 via a microbial electrochemical snorkel raised the electric potential of sediment by increasing HCl-extracted Fe(III) and NO3− concentrations while reducing DOM concentrations, which further modified microbial diversity and composition, notably reduced the relative abundance of fermentative bacteria. As a result, DOM showed the highest SUVA254 value (3.88) and SUVA280 value (1.61), preliminarily suggesting their enhanced aromaticity, humification and average molecular weight. Additionally, these DOM exhibited the highest electron transfer capacity (174.14±3.62 μmol e− /g C) and redox current. Based on these findings, we propose four possible avenues through which EAB-established LDET to O2 facilitates sediment remediation, mainly including DOM involved affinity, direct and indirect electron transfer, and induced photochemical reaction in degradation or humification process of organic contaminants. Although these proposed avenues require further verification, this work sheds light on deciphering the mechanisms underlying the augmented degradation of organic contaminants facilitated by EAB-established LDET to O2, offering fresh insights into sediment remediation.