Anaerobic Bacteria Research Articles

CD47 and thrombospondin-1 contribute to immune evasion by Porphyromonas gingivalis

Porphyromonas gingivalis is a gram-negative anaerobic bacterium linked to periodontal disease. Remarkably, P. gingivalis thrives in an inflamed environment rich in activated neutrophils. Toll-like receptor 2 (TLR2) recognition is required for P. gingivalis to evade innate immune killing; however, the mechanisms through which P. gingivalis uncouples host inflammation from bactericidal activity are only partially known. Since integrin activation and alternative signaling are implicated in P. gingivalis TLR2-mediated immune escape, we explored the role of CD47, a widely expressed integrin-associated protein known to suppress phagocytosis and implicated as an interacting partner with other innate immune receptors. We found that CD47 associates with TLR2, and blocking CD47 leads to decreased intracellular P. gingivalis survival in macrophages in a manner dependent on the bacterial major fimbria. In vivo, CD47 knock-out mice cleared P. gingivalis more efficiently than wild-type mice. Next, we found increased expression and secretion of the CD47 ligand thrombospondin-1 (TSP-1) following P. gingivalis infection. Secreted TSP-1 broadly protected P. gingivalis and other periodontitis-associated bacterial species from neutrophil bactericidal activity. Therefore, CD47-TLR2 cosignaling in response to P. gingivalis induces TSP-1 that in turn suppresses neutrophil activity, an effect that can explain how species such as P. gingivalis survive in an inflamed environment and cause dysbiosis.

Bacteriology of Aspiration Pneumonia: The Lung Microbiome and the Changing Microbial Etiology

AbstractAspiration pneumonia refers to the process of alveolar inflammation induced by the inhalation of oropharyngeal secretions into the lower respiratory tract. Predisposing factors comprise swallowing dysfunction, impaired cough reflex, and degenerative neurological diseases. Accumulating evidence projects a fading contribution of anaerobic bacteria in aspiration pneumonia at the expense of Gram-negative bacilli, with Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa, becoming the predominant organisms recovered from respiratory specimens. Aspiration of oropharyngeal secretions colonized with respiratory pathogens induces a profound disequilibrium of the lung microbiota resulting in a state of dysbiosis. Understanding this complex temporal variability between microbiome–host associations was only made possible with the introduction of metagenomic sequencing. In this narrative review, we summarize existing knowledge and elaborate on the evolving microbiology of aspiration pneumonia including the link between oral microbiome and pulmonary aspiration. We also highlight the progress and challenges in instituting microbiome-targeted strategies for preventing and treating the sequelae of aspiration pneumonia.

Structural and Functional Insight Into YefM–YoeB Complex of Toxin–Antitoxin System From Streptococcus pneumoniae

ABSTRACTStreptococcus pneumonia is a Gram‐positive and facultative anaerobic bacterium that causes a number of diseases, including otitis media, community‐acquired pneumonia, sepsis, and meningitis. With the emergence of antibiotic‐resistant strains, there is an urgent need to develop antibiotics with a novel mechanism. The toxin–antitoxin (TA) system, which is primarily found in prokaryotes, consists of a toxin and its equivalent antitoxin genes. The YefM–YoeB module is a Type II TA system, where the YoeB toxin functions as a putative mRNA interferase upon activation, while the YefM antitoxin acts as a transcription repressor by binding to its promoter region along with YoeB. In this study, we determined the crystal structure of the YefM–YoeB complex from S. pneumoniae TIGR4 to comprehend the binding mechanism of the TA system. Furthermore, an in vitro ribonuclease activity assay was conducted to identify the ribonuclease activity of the YoeB toxin. Additionally, furthermore, the oligomeric state of the YefM–YoeB complex in solution was investigated, and a DNA‐binding mode was proposed. These structural and functional insights into the YefM–YoeB complex could provide valuable information for the development of novel antibiotics targeting S. pneumonia‐associated diseases.

Description of Olsenella absiana sp. nov., an anaerobic bacterium isolated from pig faeces

A short-rod-shaped, obligate anaerobic, Gram-positive bacterium isolated from the faeces of a pig was designated as the strain YH-ols2223T. Analysis of the 16S rRNA gene sequence revealed that the isolate was most closely related to Olsenella urininfantis KCTC 25755T with 97.7% similarity. The multi-locus sequence tree revealed that the isolate formed a sub-cluster within the genus Olsenella. The average nucleotide identity and the digital DNA–DNA hybridization values for the isolate and the most closely related strains were 74.9–76.6% and 20.8–22.5%, respectively. The end products of the fermentation were lactic acid and acetic acid. The main fatty acids identified were C18 : 0 DMA, C18 : 1 ω9c DMA and C18 : 1 ω9c. The cell wall contained the meso-diaminopimelic acid-based peptidoglycan. Given the chemotaxonomic, phenotypic and phylogenetic properties, YH-ols2223T (= KCTC 25800T = NBRC 116680T) represents a novel taxon. The name Olsenella absiana sp. nov. was proposed.

Perithonsillar and parapharyngeal abscess: microbiological and morphological features

Introduction. The most dangerous local complication of acute and exacerbations of chronic inflammatory diseases of the pharynx is the formation of abscesses in the structure of the cellular spaces of the neck. Paratonsillar abscess (PTA) is the most common abscessing lesion. In turn, parapharyngeal abscess (PFA) is often found in patients with PTA as its complication.Aim. To study the clinical, microbiological and pathomorphological features of parapharyngeal complications in patients with PTA.Materials and methods. The analysis of medical records of 50 patients with diagnoses of parathonsillar and parapharyngeal abscesses who underwent inpatient treatment at the otorhinolaryngological department of the N.I. Pirogov State Clinical Hospital No. 1 in the period from September 2021 to April 2023 was carried out. The studied patients were divided into 2 groups. In group 2 of patients (n = 25; F 10, M 15; average age -37.2 years ± 10.8 years) an isolated PTA was diagnosed. In the 2 group of patients (n = 25; F 10, M 15, the average age was 44.6 years ± 14.8 years) PTA was complicated by the development of PFA.Results and discussion. Associations of facultative anaerobic and obligate anaerobic microorganisms were found in all pus aspirates obtained from PTA and PFA. Monocultures of microorganisms were not isolated in any case. The detection of Fusobacterium necrophorum was associated with pronounced necrotic changes in the tissues of the tonsils and surrounding structures; Peptostreptococcus anaerobius with purulent melting of fiber tissue; Veillonella dispar with pronounced infiltrative processes in tissues combined with oral pathology in patients.Conclusions. The most common microorganisms in patients with PTA and PFA were Streptococcus pyogenes and Fusobacterium necrophorum. The activity of Fusobacterium necrophorum is associated with a more severe course of the inflammatory process in the near-pharyngeal space.

IDENTIFICATION OF PERIODONTAL PATHOGENS IN PATIENTS WITH CHRONIC GENERALIZED PERIODONTITIS DEPENDING ON THE SEVERITY OF INFLAMMATION

Introduction. The progression of chronic generalized periodontitis is associated with gram-negative anaerobic bacteria. Microbiological diagnostics of periodontal disease provides an opportunity for selecting the most effective therapeutic approach for both local and systemic conditions in patients. Aim of this study is to conduct a qualitative assessment of the presence of pathogenic microorganisms in the periodontal pockets of patients, based on the severity of inflammation. Materials and methods. The presence of five key pathogenic microorganisms in the periodontal pocket contents of 90 individuals aged 25-60 years (45 with grade I severity and 45 with grade II) was assessed using real-time polymerase chain reaction (PCR). The analysis was conducted with the CFX96™ Real-Time PCR Detection System (BIO-RAD) and the PeriodontScreen Real-TM reagent kit (Sacace Biotechnologies Srl, Italy). Non-parametric correlation statistical analysis was performed to calculate Kendall’s Tau and Gamma coefficients. In 27 patients (60%) with grade I severity, bacteria of a single species were identified. Two types of periodontal pathogens were detected in 13 patients (28.9%), with the most common combination being Tannerella forsythia and Aggregatibacter actinomycetemcomitans, found in 5 patients (11.1%); 5 patients (11.1%) showed the presence of three microbial species: Tannerella forsythia, Treponema denticola, and Porphyromonas gingivalis. Among the patients with grade II severity, 8 patients (17.8%) had bacteria of one species, specifically Prevotella intermedia. Two microbial species were identified in 9 patients (20%), while three species were present in 15 patients (33.3%). The most frequent combination included Prevotella intermedia, Tannerella forsythia, and Aggregatibacter actinomycetemcomitans, found in 5 patients (11.1%). Four types of microbes were detected in 13 patients (28.9%), with the predominant combination being Tannerella forsythia, Porphyromonas gingivalis, Treponema denticola, and Aggregatibacter actinomycetemcomitans (17.8%). None of the patients with grade II severity had all five periodontopathogenic agents. The correlation analysis confirmed that chronic periodontitis is strongly associated with the presence of Tannerella forsythia within microbial associations. Conclusions. The spectrum of periodontal pathogens affects the severity of inflammation in the periodontium. In grade II inflammation, associations of periodontal pathogens were detected by 82.2% of cases, while in grade I by in 40%. Tannerella forsythia was detected in 42.2% of patients with grade I inflammation, 15.6% of them as a mono-infection; in patients with grade II inflammation in 71.1%, in associations with Treponema denticola in 48.9%. Determining the spectrum of periodontal pathogens, taking into account their characteristics and associated virulence factors, is necessary for choosing the effective differentiated treatment approach.

Electrochemically Coupled Anaerobic Membrane Bioreactor Facilitates Remediation of Microplastic-Containing Wastewater

Ubiquitous microplastics (MPs) severely affect the efficiency of anaerobic membrane bioreactors (AMBR) for wastewater treatment and energy recovery by inhibiting the metabolic activity of anaerobic microorganisms. The electrochemical system can not only accelerate waste metabolism but also improve microbial resistance by promoting interspecies electron transfer within the system, which has broad application potential in the remediation of MPs wastewater. This paper attempts to evaluate the effect of electrical stimulation on the efficiency of biological wastewater treatment processes containing MPs employing an electrochemical system coupled to an anaerobic membrane bioreactor (ECAMBR). The results showed that although MP exposure inhibited methanogenic performance, electrical stimulation effectively alleviated this inhibitory effect. Further analysis showed that microplastics increased cell damage and affected enzyme activity, but electrical stimulation could affect the stress response of microorganisms, leading to changes in their cell viability and enzyme activities. The 16S-rRNA sequencing indicated that the highest abundance of hydrolytic–acidogenic bacteria Firmicutes and Bacteroidota was found at the phylum level, whereas at the genus level, it was Christensenellaceae_R-7_group, and methanogens were dominated by Methylomonas, Methyloversatilis, and Methylobacter. Functional prediction analysis indicated that carbohydrate metabolism, amino acid metabolism, and energy metabolism were the dominant metabolic pathways and that electrical stimulation could enhance their activities. This study demonstrated the important role of electrochemical stimulation in the remediation of wastewater containing high concentrations of MPs.

Growth substrate limitation enhances anaerobic arsenic methylation by Paraclostridium bifermentans strain EML.

Microbial arsenic methylation is established as a detoxification process under aerobic conditions (converting arsenite to monomethylated arsenate) but is proposed to be a microbial warfare strategy under anoxic conditions due to the toxicity of its main product, monomethylarsonous acid (MMAs(III)). Here we leveraged a paddy soil-derived anaerobic arsenic methylator, Paraclostridium bifermentans strain EML, to gain insights into this process. Strain EML was inoculated into a series of media involving systematic dilutions of Reinforced Clostridial Broth (RCB) with 25 µM arsenite to assess the impact of growth substrate concentration on arsenic methylation. Growth curves evidenced the sensitivity of strain EML to arsenite, and arsenic speciation analysis revealed the production of MMAs(III). Concentrations of MMAs(III) and arsenic methylation gene (arsM) transcription were found to be positively correlated with RCB dilution, suggesting that substrate limitation enhances arsM gene expression and associated anaerobic arsenic methylation. We propose that growth substrate competition among microorganisms may also contribute to an increase in anaerobic arsenic methylation. This hypothesis was further evaluated in an anaerobic co-culture system involving strain EML and either wild-type Escherichia coli K-12 MG1655 (WT) or E. coli expressing the MMAs(III)-resistance gene (arsP) (ArsP E. coli). We observed increased MMAs(III) production in the presence of E. coli than its absence and growth inhibition of WT E. coli to a greater extent than ArsP E. coli, presumably due to the MMAs(III) produced by strain EML. Collectively, our findings suggest an ecological role for anaerobic arsenic methylation, highlighting the significance of microbe-microbe competition and interaction in this process.IMPORTANCEMicrobial arsenic methylation is highly active in rice paddy fields under flooded conditions, leading to increased accumulation of methylated arsenic in rice grains. In contrast to the known detoxification process for aerobic arsenic methylation, the ecological role of anaerobic arsenic methylation remains elusive and is proposed to be an antibiotic-producing process involved in microbial warfare. In this study, we interrogated a rice paddy soil-derived anaerobic arsenic-methylating bacterium, Paraclostridium bifermentans strain EML, to explore the effect of growth substrate limitation on arsenic methylation in the context of the microbial warfare hypothesis. We provide direct evidence for the role of growth substrate competition in anaerobic arsenic methylation via anaerobic prey-predator co-culture experiments. Moreover, we demonstrate a feedback loop, in which a bacterium resistant to MMAs(III) enhances its production, presumably through enhanced expression of arsM resulting from substrate limitation. Our work uncovers the complex interactions between an anaerobic arsenic methylator and its potential competitors.

Psychoneurological disorders in the stage of post-COVID syndrome

Аim. Generalization and systematization of ideas about the pathophysiological mechanisms of asthenic syndrome development against the background of COVID-19.Materials and methods. The work analyzed scientific articles and monographs devoted to the etiopathogenesis of post-COVID asthenic syndrome (PCAS). The search was carried out by the keywords «COVID-19», «post-COVID syndrome», «psychoneurological disorders», «asthenic syndrome» using the PubMed, Medline, eLibrary.ru databases.Results and discussion. The ideas about the clinical structure of PCAS are systematized, the mechanisms of penetration of the SARS-CoV-2 virus into the nervous system are presented, modern views on the molecular mechanisms of the development of neurological symptoms in COVID-19 convalescents are highlighted. The key pathogenetic links of PCAS are described, including immune deviations associated with cytokine imbalance, oxidative and nitrosative stress reactions with subsequent activation of anaerobic metabolic pathways in brain and muscle tissues; neurometabolic changes accompanied by dysfunction of the serotonergic, dopaminergic, noradrenergic and GABAergic systems.Conclusion. Analysis of world literature data, as well as our own clinical experience, allows us to conclude that psychoneurological disorders associated with COVID-19 infection are multifaceted and complex and are accompanied by highly variable symptoms. At the same time, the existing fragmentary knowledge regarding the pathomechanisms of psychoneurological disorders against the background of COVID-19 dictates an urgent need to continue further research in this area.

Natural Antimicrobial Monoterpenes as Potential Therapeutic Agents in Vaginal Infections: A Review

The recurrence and relapse of vaginal infections in women is a major issue and a challenging pathway to identify and develop new approaches to treatment. In the case of antibiotic therapy, contraceptives, and dietary changes, the recurrence of vaginitis is more common these days. Anaerobic bacteria, Candida spp., and trichomonas in the vaginal microflora cause both symptomatic and asymptomatic vaginitis, which includes vaginal inflammation. It changes the vaginal microbiota and decreases Lactobacilli spp. growth, which is maintaining the vaginal pH (3.5-4.5) through lactic acid production, antimicrobial peptides, bacteriocin, and bacteriocin-like inhibitory substances. The remarkable antimicrobial activity of plant’s producing metabolites like alkaloids, tannins, phenolic compounds, flavonoids and terpenoids for several vaginal infections have been reported in previous studies. Presented review focuses on the pivotal role of monoterpenes, providing a detailed description of thymol, geraniol, limonene, eugenol, eucalyptol, and α-terpineol as antimicrobial molecules in the treatment of vaginal infections. These monoterpenes are very good at killing E. coli, Staphylococcus aureus, Pseudomonas aeruginosa, Aspergillus niger, Trichomonas vaginalis and Candida albicans which are the main microbes that cause vaginitis. Future research could explore the latent combinations of such monoterpenes as synergistic antimicrobial agents to treat bacterial and fungal vaginal infections, trichomoniasis, among other conditions.

The Impact of Triclosan-Containing Toothpaste on the Overall and Cariogenic Salivary Microbiota Among Primary School Children

Objectives: Triclosan-diphenyl ether derivate is an agent, which belongs to the Non-Ionic antimicrobial agents group. This study aims to estimate the salivary levels of Streptococcus mutans and Lactobacillus species in the saliva before and after teeth brushing with a dentifrice containing triclosan/copolymer and to compare the number of whole salivary flora by saliva analysis before and after teeth brushing. Methods: To accomplish our objective, we used a Colgate Total Plus Whitening®, Colgate-Palmolive dentifrice. The group consisted of 24 healthy schoolchildren aged 9 – 13 of both sexes. The counts of Streptococcus mutans and Lactobacillus species were determined with commercial CRT bacteria strips produced by Ivoclar-Vivadent, Liechtenstein. The total count of the saliva microbial was determined by standard microbiological methods. Results: A significant reduction in salivary MS and LB levels was observed in all samples as well as a decrease in the total count of aerobe and anaerobe bacteria and yeast. Conclusion: The effectiveness of Colgate Total Plus Whitening® toothpaste in reducing salivary aerobes is statistically significant, but its impact on reducing salivary anaerobic microbes is statistically negligible. The bacteria Streptococcus mutans experiences a decrease that is greater than tenfold, while the bacterium Lactobacillus species experiences a reduction of around tenfold.

Study of Bacillus cereus as an Effective Multi-Type A Trichothecene Inactivator

Type A trichothecenes are common mycotoxins in stored cereal grains, where co-contamination is likely to occur. Seeking new microbiological options capable of inactivating more than one type A trichothecene, this study aimed to analyze facultative anaerobe bacteria isolated from broiler proventriculus. For this purpose, type A trichothecenes were produced in vitro, and a facultative anaerobic bacterial consortium was obtained from a broiler’s proventriculus. Then, the most representative bacterial strains were purified, and trichothecene inactivating assays were performed. Finally, the isolate with the greatest capacity to remove all tested mycotoxins was selected for biosorption assays. The results showed that when the consortium was tested, neosolaniol (NEO) was the most degraded mycotoxin (64.55%; p = 0.008), followed by HT-2 toxin (HT-2) (22.96%; p = 0.008), and T-2 toxin (T-2) (20.84%; p = 0.014). All isolates were bacillus-shaped and Gram-positive, belonging to the Bacillus and Lactobacillus genera, of which B. cereus was found to remove T-2 (28.35%), HT-2 (32.84%), and NEO (27.14%), where biosorption accounted for 86.10% in T-2, 35.59% in HT-2, and 68.64% in NEO. This study is the first to prove the capacity of B. cereus as an effective inactivator and binder of multi-type A trichothecenes.

Update on novel validly published and included bacterial taxa derived from human clinical specimens and taxonomic revisions published in 2023.

Taxonomy is a systematic practice in which microorganisms are granted names to facilitate and standardize multi-disciplinary communication. We summarize novel bacterial taxa derived from human clinical material that were published in peer-reviewed literature and/or included by the International Journal of Systematic and Evolutionary Microbiology during calendar year 2023, as well as taxonomic revisions that have been published/included by the same entity. While the majority of newly discovered facultative and anaerobic organisms were derived from microbiome surveillance, noteworthy novel taxa in the realm of pathogenicity potential include those related to Aerococcus spp., several Corynebacterium spp., Exercitatus varius gen. nov., sp. nov., and Mycoplasma phocimorsus sp. nov. With respect to nomenclature revision, the Bacillus and Clostridium genera continue to be visited annually. Creation of novel anaerobic Gram-negative bacillus genera Hallella, Hoylesella, Leyella, Segatella, and Xylanibacter impacted several Bacteroides spp. and Prevotella spp. Additional studies are necessary to ascertain the clinical significance of several of these microbes.

Altitude shapes gut microbiome composition accounting for diet, thyroid hormone levels, and host genetics in a subterranean blind mole rat

The animal gut microbiome acts as a crucial link between the host and its environment, playing a vital role in digestion, metabolism, physiology, and fitness. Using 16S rRNA metabarcoding, we investigated the effect of altitude on the microbiome composition of Anatolian Blind Mole Rats (Nannospalax xanthodon) across six locations and three altitudinal groups. We also factored in the host diet, as well as host microsatellite genotypes and thyroid hormone levels. The altitude had a major effect on microbiome composition, with notable differences in the relative abundance of several bacterial taxa across elevations. Contrary to prior research, we found no significant difference in strictly anaerobic bacteria abundance among altitudinal groups, though facultatively anaerobic bacteria were more prevalent at higher altitudes. Microbiome alpha diversity peaked at mid-altitude, comprising elements from both low and high elevations. The beta diversity showed significant association with the altitude. Altitude had a significant effect on the diet composition but not on its alpha diversity. No distinct altitude-related genetic structure was evident among the host populations, and no correlation was revealed between the host genetic relatedness and microbiome composition nor between the host microbiome and the diet. Free thyroxine (FT4) levels increased almost linearly with the altitude but none of the bacterial ASVs were found to be specifically associated with hormone levels. Total thyroxine (TT4) levels correlated positively with microbiome diversity. Although we detected correlation between certain components of the thyroid hormone levels and the microbiome beta diversity, the pattern of their relationship remains inconclusive.

Enhancing simultaneous nitrogen and phosphorus removal using partial nitritation/anammox with an airlift inner-circulation partition bioreactor

The partial nitritation/anammox (PNA)-hydroxyapatite (HAP) process for synchronized nitrogen (N) and phosphorus (P) removal has attracted much attention; however, its use has been restricted by the limited availability of optimal bioreactor configuration and its operational conditions. In the present study, a new single-stage PNA reactor, the airlift inner-circulation partition bioreactor (AIPBR), was continuously operated for 261 days at a fixed hydraulic retention time of 6 h. The results showed that the optimal removal performance (ammonia, 92.77 ± 0.72 %; total N, 76.92 ± 1.78 %; %, total P, 86.57 ± 2.84 %) was achieved at a Ca/P ratio of 4.0 during the operation period; the influent ammonia and P concentrations were maintained at 250 mg/L and 20 mg/L, respectively. The P removal efficiency was 10 % higher than that reported in similar studies, indicating that a highly efficient PNA-HAP process can be successfully achieved using the AIPBR. By enhancing the circulation of the mixture between the inner and outer layers, accelerating the accumulation of ammonia-oxidizing and anaerobic ammonia-oxidizing bacteria, and promoting simultaneous biological autotrophic denitrification and phosphorization, the sludge granulation and HAP crystallization were gradually strengthened by the pH increase inside the sludge particles. Our findings provide a scientific basis for developing next-generation technologies for synchronized N and P removal from wastewater.

Sodium butyrate activates the extrinsic and intrinsic apoptotic processes in murine cementoblasts

Background/purpose: The metabolic by-product butyric acid of Gram-negative anaerobic bacteria can invoke pathological effects on periodontal cells resulting in inflammation and further destruction of periodontium. However, limited researches on the effects of butyric acid on cementoblasts were reported. Therefore, this study aimed to investigate the type of cell death in murine cementoblast (OCCM.30) caused by adding the different concentrations of sodium butyrate to the cell culture. Materials and methodsOCCM.30 cells were exposed to sodium butyrate (0, 2, 4, 8, 16 mM) for 48 h. Cell viability was determined by microculture tetrazolium assay. Cell cycle distribution and cell death were analyzed by flow cytometry. Caspase-mediated apoptotic cascade was evaluated by Western blot. ResultsThe concentrations of sodium butyrate≧4 mM were found to inhibit cell viability of OCCM.30 cells in a dose-dependent manner (P < 0.05). Sodium butyrate elevated sub-G1 cell population which exhibited cell apoptosis in OCCM.30 cells (P < 0.05). In addition, early and later apoptotic cells were found in sodium butyrate-induced cell death. Sodium butyrate significantly stimulated the degradation of procaspases-3, -8, and -9 levels, respectively (P < 0.05). Simultaneously, sodium butyrate corresponded to augment the levels of cleaved forms of caspases-3, -8, and -9, respectively (P < 0.05). ConclusionTaken together, sodium butyrate is a cytotoxic agent and can induce apoptosis on cementoblasts. The pathway involved in apoptosis is activated by caspase family signaling pathways. These evidences may provide a new mechanistic insight into the mechanism of damage of cementoblasts during the development and progression of periodontitis.

Effects of different quorum sensing signal molecules on alleviation of ammonia inhibition during biomethanation

Anaerobic digestion (AD) is a promising technology for achieving both organic wastes treatment and energy recovery. However, challenges such as ammonia inhibition still remain. Quorum sensing (QS) system is relevant with the regulation of microbial community behaviors by releasing and sensing signal molecules, which could improve methane production during AD process. Therefore, the current study explored the effects of different quorum sensing signal molecules on alleviation of ammonia inhibition. The results showed that both secretion of N-butyryl-DL-homoserine lactone (C4-HSL) and N-(β-ketocaproyl)-DL-homoserine lactone (3OC6-HSL) could be inhibited by high ammonia stress while stimulation of N-hexanoyl-L-homoserine lactone (C6-HSL) and N-octanoyl-DL-homoserine lactone (C8-HSL) secretion might be triggered by ammonia toxicity. Moreover, the alleviation of ammonia inhibition could be achieved by both introducing 3OC6-HSL (0.5 μM) and combination of 3OC6-HSL (0.1 μM) and biochar (4 g/L). Exogenous 3OC6-HSL could regulate microbial social behaviors and enhance the secretion of extracellular polymeric substances (EPS) to promote anaerobic digestion. In addition, the mitigation of ammonia inhibition through exogenous 3OC6-HSL and biochar were confirmed by microbial community changes (Methanobacterium, Propionicicella and Petrimonas). Critical enzymes involved in both acidification and methanogenic steps were enhanced after adding the combination of 3OC6-HSL and biochar. The combination of low levels of 3OC6-HSL and biochar could promote both direct interspecies electron transfer (DIET) process and communication between different anaerobic microorganisms to mitigate ammonia inhibition. The current study will provide primary insights for conquering ammonia inhibition during biomethanation.

Advanced anaerobic digestion by co-immobilization of anaerobic microbes and conductive particles in hydrogel for enhanced methane production performance

Recent research has increasingly focused on the enhancement of anaerobic digestion (AD) through direct interspecies electron transfer (DIET) facilitated by conductive particles (CP). Although this approach can significantly accelerate the AD process, the contact efficiency between CPs and AD microbes is relatively low due to the flow of water in a dispersed condition, leading to possible DIET inefficiency. In this study, a unique approach involving the “co-immobilization” of anaerobic microbes and multi-walled carbon nanotubes (MWCNTs) as CP into a hydrogel matrix was developed to improve the AD process. The advantages of this method include improved contact efficiency between microbes and CPs for enhanced DIET, and increased CP retention within the reactor, thereby omitting the need to compensate for CP washout. The methane production rate for the co-immobilized hydrogel was 2.5-fold and 1.9-fold faster than that of the control (dispersed sludge) and conventional DIET (dispersed sludge with MWCNT addition), respectively. Microbial analysis indicated the enrichment of functional microbes such as Anaerolineacea, Sedimentibacteraceae, Rhodocyclaceae, and Methanothrichaceae, which could be involved in the DIET under co-immobilized conditions. These results demonstrate the potential of the proposed method for realizing an advanced continuous AD process through improved DIET.

Stochastic Processes Dominate the Assembly of Soil Bacterial Communities of Land Use Patterns in Lesser Khingan Mountains, Northeast China

To meet the demands of a growing population, natural wetlands are being converted to arable land, significantly impacting soil biodiversity. This study investigated the effects of land use changes on bacterial communities in wetland, arable land, and forest soils in the Lesser Khingan Mountains using Illumina MiSeq 16S rRNA sequencing. Soil physicochemical properties and enzyme activities were measured using standard methods, while microbial diversity was assessed through sequencing analysis. Our findings revealed that forest soils had significantly higher levels of total potassium (2.62 g·kg−1), electrical conductivity (8.22 mS·cm−1), urease (0.18 mg·g−1·d−1), and nitrate reductase (0.13 mg·g−1·d−1), attributed to rich organic matter and active microbial communities. Conversely, arable soils showed lower total potassium (1.94 g·kg−1), reduced electrical conductivity, and suppressed enzyme activities due to frequent tilling and fertilization. Wetland soils exhibited the lowest values primarily due to water saturation, which limits organic matter decomposition and microbial activity. Land use changes notably reduced microbial diversity, with conversion from forest to arable land leading to habitat loss. Forest soils supported higher abundances of Proteobacteria (37.59%) and Actinobacteriota (34.73%), while arable soils favored nitrogen-fixing bacteria. Wetlands were characterized by chemoheterotrophic and anaerobic bacteria. Overall, these findings underscore the profound influence of land use on soil microbial communities and their functional roles, highlighting the need for sustainable management practices.

Unraveling Cecal Alterations in Clostridioides difficile Colonized Mice through Comprehensive Metabolic Profiling.

The disruption of gut microbiota caused by antibiotics favors the intestinal colonization of Clostridioides difficile - a Gram-positive, spore-forming anaerobic bacterium that causes potentially fatal gastrointestinal infections. In an endeavor to elucidate the complexities of the gut-brain axis in the context of Clostridium difficile infection (CDI), a murine model has been used to investigate the potential effects of antibiotic administration and subsequent colonization by C. difficile, as well as the impact of three different 10-day treatments (metronidazole, probiotics, and fecal microbiota transplantation), on the cecal metabolome for the first time. This follows our previous research which highlighted the metabolic effect of CDI and these treatments in the brain and employs the same four different metabolomics-based methods (targeted GC-MS/MS, targeted HILIC-MS/MS, untargeted RP-LC-HRMS/MS and untargeted GC-MS). A total of 286 unique metabolites have been identified in the mouse cecal profiles and statistical analysis revealed that CDI, as well as the subsequent treatments, significantly alters cecal metabolites and lipids implicated in various biochemical pathways centered around amino acid metabolism, glycerophospholipid metabolism, and central carbon metabolism. To our knowledge, this study represents the first exploration of the effects of C. difficile-induced colitis and potential treatments on the cecal tissue metabolome.