Filamentous Bacteria Research Articles

Multi-scale feature flow alignment fusion with Transformer for the microscopic images segmentation of activated sludge

Accurate microscopic images segmentation of activated sludge is essential for monitoring wastewater treatment processes. However, it is a challenging task due to poor contrast, artifacts, morphological similarities, and distribution imbalance. A novel image segmentation model (FafFormer) was developed in the work based on Transformer that incorporated pyramid pooling and flow alignment fusion. Pyramid Pooling Module was used to extract multi-scale features of flocs and filamentous bacteria with different morphology in the encoder. Multi-scale features were fused by flow alignment fusion module in the decoder. The module used generated semantic flow as auxiliary information to restore boundary details and facilitate fine-grained upsampling. The Focal–Lovász Loss was designed to handle class imbalance for filamentous bacteria and flocs. Image-segmentation experiments were conducted on an activated sludge dataset from a municipal wastewater treatment plant. FafFormer showed relative superiority in accuracy and reliability, especially for filamentous bacteria compared to existing models.

Microbiota-Specific T Cells Contribute to Graft-Versus-Host Disease after Allogeneic Stem Cell Transplantation

Background: Allogeneic T-cell expansion is the primary determinant of graft-versus-host disease (GVHD), and current dogma dictates that this is driven by histocompatibility antigen disparities between donor and recipient. This paradigm represents a fixed genetic system within which donor T cells interact with recipient-derived peptide-MHC complexes. However, the current model does not account for potential cognate interactions between donor T cells and microbe-derived antigen presented by the recipient. Prior studies in healthy patients have demonstrated the existence of circulating αβT cells targeting common bacterial species in the gastrointestinal (GI) tract. Whether microbe-specific T cells derived from the donor graft impact GVHD outcomes has not been studied. We tested the hypothesis that the recipient GI microbiota serve as a source of cognate antigen, contributing to clonotypic donor T-cell expansion and induction of GVHD. Methods: Functional studies utilized allogeneic stem cell transplant models in murine systems including both matched (Marilyn Tg to B6 male) and mismatched (B6 to B6D2F1) transplants as well as inducible MHCII knockout mice. Microbiota-specific transgenic T cells (MSTCs) targeting commensal flagellin (CBir1) and vendor-specific microbiome (segmented filamentous bacteria - SFB) in the context of I-A(b) were incorporated as part of the donor graft. Mechanistic studies utilized flow cytometry, cytokine stimulation and profiling, single-cell RNA sequencing, gene set enrichment analysis, NFAT-GFP T-hybridoma reporters, live-cell imaging (xCelligence RTCA eSight), and tissue analysis with RNA in-situ hybridization (ISH). Results: MSTCs lethally augmented GVHD when given as part of the donor graft in respectively colonized recipients. Taconic B6 male recipients (SFB-bearing) developed lethal GVHD when both donor Marilyn (Allo) Tg T cells and SFB T cells were introduced, but not when either transgenic T cell was introduced alone ( Figure A, p<0.0001). In contrast, Jackson B6 recipients (SFB-absent) receiving both Allo and SFB T cells did not develop lethal GVHD ( Figure A, p<0.0001), confirming functional relevance of microbe-specificity among the donor T cell pool. Lethal GVHD was also seen with addition of CBir1 T cells to the donor graft but not with addition of bulk T cells (log-rank p<0.0001). Similar results were seen in a mismatched transplant system. To determine how MSTCs promoted lethality in the context of an allogeneic (allo) response, we performed scRNA sequencing of T cells harvested in the recipient spleen at day 6 post-transplant (prior to mortality onset). Post-transplant MSTCs harbored a naïve phenotype (Sell high/CD44 low/CD69 low) when given as the primary source of donor T cells but shifted to an early activated phenotype (Sell int/CD44 low/CD69 high/TCF7 low) when Allo T cells were concurrently introduced (ANOVA q<0.01). MSTC activation was confirmed with augmented expression of IFNγ upon PMA/ionomycin stimulation observed in allo vs. syngeneic response (Wilcoxon rank-sum, p< 0.01). Introduction of Allo T cells increased the abundance of MSTCs in the mesenteric lymph nodes (day 5, 6, Wilcoxon, p<0.01). Ablation of MHCII on the GI epithelial surface using Villin-CreERT2 I-Ab flox recipients abrogated microbe-specific T cell activation in co-culture with recipient GI intraepithelial cells harvested at day 6 post-transplant vs. non-ablated control (8, 12, 24-hr NFAT-GFP intensity, p<0.001). RNA ISH probes targeting the CDR3 region of anti-microbial CBir1 T cells demonstrated an increase in MSTC infiltration at day 6 in the recipient GI lamina propria during an allo response ( Figure B) compared to a syngeneic response (# of MSTCs/terminal ileum cross section at day 6, Wilcoxon p<0.01). Conclusions: We confirm that clonotypic T cell expansion following allogeneic transplantation is not only driven by donor-recipient genetics, as reflected by major and minor histocompatibility matching, but also by differences in microbiota composition that can serve as a source of antigenic stimulation, providing a feed-forward mechanism to propagate GVHD. Furthermore, in the context of an alloreactive T cell response that damages gut integrity, microbial antigens can be presented by GI epithelia, allowing the gut to be concurrently targeted by microbiota specific T cells whose function is additionally enhanced by the alloreactive response.

A post-transplant infection by Nocardia cyriacigeorgica

Nocardia are Gram-positive, acid-fast, filamentous bacteria that cause opportunistic infections in susceptible populations. We describe a case of post-transplant infection of pulmonary nocardiosis caused by the rare strain Nocardia cyriacigeorgica and the challenges faced in reaching a definitive diagnosis. This case report emphasizes on keeping nocardiosis as a differential diagnosis in transplant recipients, as this disease is largely underdiagnosed and underreported.

Segmented filamentous bacteria-induced epithelial MHCII regulates cognate CD4+ IELs and epithelial turnover.

Intestinal epithelial cells have the capacity to upregulate MHCII molecules in response to certain epithelial-adhesive microbes, such as segmented filamentous bacteria (SFB). However, the mechanism regulating MHCII expression as well as the impact of epithelial MHCII-mediated antigen presentation on T cell responses targeting those microbes remains elusive. Here, we identify the cellular network that regulates MHCII expression on the intestinal epithelium in response to SFB. Since MHCII on the intestinal epithelium is dispensable for SFB-induced Th17 response, we explored other CD4+ T cell-based responses induced by SFB. We found that SFB drive the conversion of cognate CD4+ T cells to granzyme+ CD8α+ intraepithelial lymphocytes. These cells accumulate in small intestinal intraepithelial space in response to SFB. Yet, their accumulation is abrogated by the ablation of MHCII on the intestinal epithelium. Finally, we show that this mechanism is indispensable for the SFB-driven increase in the turnover of epithelial cells in the ileum. This study identifies a previously uncharacterized immune response to SFB, which is dependent on the epithelial MHCII function.

Acidifying remediation and microbial bioremediation decrease ammoniacal nitrogen, orthophosphates, and total suspended solids levels in intensive Nile tilapia farming under biofloc conditions

In biofloc technology (BFT) systems, the formation of bioflocs and accumulation of suspended solids are constant, which can cause impairments in water quality parameters and negatively impact the growth performance of farmed animals. We herein investigated two integrated solutions for intensive farming of Nile tilapia under BFT conditions. In this study, EUROGUARD® SOFT F60 (60% formic acid and 40% lignosulfonic acid) was used as the acidifying remediator, while ADD LIFE PRO BACIL ACQUA based on a mixture of Bacillus spp. was used as the microbial bioremediator. First, assays were conducted for in vitro inhibition tests of acidifying remediator against seven different strains of pathogenic bacteria. A dose-response test was performed for both acdifying bioremediator and microbial bioremediator. Then, an in vivo assay was conducted over four weeks. In 12 BFT units with a capacity of 250 L each, one group received the acidifying remediator at a concentration of 2.5 part per million (ppm), while another group received the bioremediator Bacillus spp. at a concentration of 0.10 g m−3 directly in tank water. A control group without aditives was also established, all in quadruplicate. The culture environment was evaluated daily by measuring dissolved oxygen, temperature, floc volume and weekly by measuring total ammonia nitrogen (TAN), ammoniacal nitrogen (N−NH3), nitrite (N-NO2), nitrate (N-NO3), alkalinity (CaCO3), orthophosphate (PO43−), electrical conductivity (μS−1), potential of hydrogen (pH) and total suspended solids (TSS). At the end of the period, in the in vivo assay, the bacterial community in the BFT, hematological parameters, and zootechnical performance of the tilapia were evaluated. In in vitro inhibition tests, the acidifying remediator inhibited the growth of all pathogenic bacteria evaluated. All concentrations reduced the count of filamentous bacteria, and the pH values were dose-dependent. Both in vivo treatments altered bacterial communities. Both treatment groups had lower concentrations of N-NH3, N-NO2 and N-NO3. PO43− content was lower in the acidifying remediator group. CaCO3 was higher in the treatment groups, while TSS was higher in the control group. Both remediation strategies were efficient in removing nitrogenous chemical compounds. However, the acidifying remediator concomitantly reduced N-NH3, N-NO2− and PO43− levels, becoming a powerful ally in the reduction of aquaculture effluents, as well as in the reduction of potentially pathogenic bacteria in tilapia culture.

Pericardial infiltration and constriction due to cardiac actinomycosis—case report

Abstract Background Constrictive pericarditis associated with actinomycosis infection is a rare and challenging diagnosis due to its insidious manifestation. We describe the successful treatment of pericardial infiltration and constriction due to actinomycosis. Case summary A 50-year-old Aboriginal man presented with insidious onset of fatigue, dyspnoea, pleuritic chest pain, fever, drenching sweats, severe exercise intolerance to 50 m, and recurrent itchy skin lesions over 8 months. Prior investigations, including serial fluorodeoxyglucose (FDG)-Positron emission tomography scans, found a progressively enlarging, metabolically active anterior mediastinal mass with two biopsies on separate occasions showing no malignancy, granulomas, tuberculosis, or other pathology. Screening for infective, autoimmune, and connective tissue disease was negative. A transthoracic echocardiogram (TTE) showed fibrinous pericarditis with extensive myocardial tethering and constrictive physiology confirmed on heart catheterization. A pericardial biopsy showed inflammatory tissue only. Biopsy of a skin lesion on the buttock showed abscess formation with Splendore Hoeppli phenomenon with Gram-positive and Grocott-positive filamentous bacteria suggestive of actinomyces, confirmed by 16S rRNA gene sequencing. He was diagnosed with cardiac actinomycosis, likely due to mediastinal infiltration from a lung infection, with haematogenous spread and treated with Penicillin G with adjunctive high-dose steroid therapy with resolution of symptoms and marked improvement in TTE features of constriction after 6 weeks. Discussion Actinomycosis is an extremely rare cause of pericardial infiltration and constriction yet highly sensitive to penicillin, highlighting the importance of accurate diagnosis. Corticosteroids are a useful adjunct to prevent chronic constrictive pericarditis and to avoid the high morbidity and mortality associated with pericardiectomy.

Production, Purification, Characterization and Anti biofilm activity of natural antibiotic by Actinokineospora cibodasensis from marine water

Health sector faces a distress globally because of the scarcity of newer antibiotics against drug resistant pathogens. Innovations in developing new antibiotics is the solution to combat the drug resistant pathogens. This alarming situation requires advanced, potential and effective antibiotics. Secondary metabolite products from microbes remain as the main origin for many of the antibiotics in the market today and are also found to be promising till date. Out of the microbes, the major share of antibiotic production is reported by Actinomycetes, which are Gram positive, anaerobic, filamentous bacteria. They are currently being exploited through new approaches to improve the efficiency of commercially valuable antibiotics. Since natural environment stands a potential source of innovative and novel antimicrobials, this investigation was performed to test the potential of selected marine actinomycetes. Of the screened ones, Actinokineospora is potential enough to cease the growth of biofilm formation. This strain was identified by molecular characterization as Actinokineospora cibodasensis. It was selected to extract secondary metabolites by submerged fermentation and made to undergo further purification and structural analyses for the search of bioactive components. Presence of streptomycin like compound by Gas Chromatography Mass Spectrometry led to a breakthrough in the study which had been confined by High Performance Thin Layer Chromatography and Fourier Transform Infra-Red Spectroscopy techniques by comparing with standards. Gene expression studies showed that the selected strain can down regulate the genes in the formation of biofilm by the test organism Pseudomonas aeruginosa. The bioactive compound from Actinokineospora is an ecofriendly product along with a biofilm mitigating activity on medical devices. Rare actinomycetal isolate was able to produce the antibiotic which could apply on medical device to reduce the infections during the treatment. This antibiotic coating on life saving devices will provide the ultimate protection for patients.

Polycladospora coralii gen. nov., sp. nov., a novel member of the family Thermoactinomycetaceae isolated from stony coral in the South China Sea.

Two novel filamentous bacteria, designated as IB182353T and IB182357, were isolated from stony coral of the South China Sea. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strains IB182353T and IB182357 were closely related to Hazenella coriacea DSM 45707T (with 93.4 and 93.5% similarity, respectively). The average nucleotide identity, average amino acid identity and digital DNA-DNA hybridization results showed that the pairwise similarities between isolate IB182353T and the other recognized Thermoactinomycetaceae species were less than 68.9, 60.5 and 21.1 %, respectively. Both strains produced aerial and substrate mycelia, grew optimally at 25-30 °C, pH 8.0-9.0 and with 2-3 % (w/v) NaCl. The cell-wall peptidoglycan type was meso-DAP and the whole-cell hydrolysates contained ribose. The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified aminophospholipid and three unidentified phospholipids. The genomic DNA G+C content was 39.5 mol%. Strain IB182353T was distinguishable from its related type strains by the contents of two fatty acids, iso-C15 : 0 and iso-C17 : 1 ω10c. Based on polyphasic taxonomic characterization, we propose that strains IB182353T and IB182357 represent a novel genus and species within the family Thermoactinomycetaceae, for which the name Polycladospora coralii gen. nov. sp. nov. is proposed. The type strain is IB182353T (=MCCC 1K04631T=JCM 34206T).

Bulking of activated sludge in the biological treatment of municipal and industrial wastewater, due to the massive development of filamentous bacteria Type 021N

A research of the causes and consequences of bulking of activated sludge was conducted at existing biological wastewater treatment plants (municipal and local at an industrial enterprise). The filamentous bacterium that was caused the bulking of the activated sludge in the studied treatment plants was identified as Type 021N. It was established that the studied filamentous bulking causes a significant deterioration of the technological characteristics of activated sludge flocs and it is accompanied by suppression of the nitrification process. To suppress the bulking of activated sludge two methods of suppressing the inflow of hydrogen sulfide into biological treatment plants were successfully used: blowing from wastewater at municipal treatment plants and inhibiting its formation at local treatment plants in the settling and laminar flow zones.

Dynamic calibration of a new secondary settler model using Cand. Microthrix as a predictor of settling velocity

Climate change is projected to increase the frequency of hydraulic shocks on urban water systems, affecting water resource recovery facilities (WRRFs). In these facilities, the settleability of activated sludge is a critical hydraulic bottleneck. However, to date, the dynamic prediction of hindered settling velocity (v0/rH) has remained unresolved. To address this significant knowledge gap, this study presents an assessment of microbial community predictors of hindered settling velocity. Through a regression analysis of independent laboratory and full-scale experimental data, we identified a close association between the relative abundance of Candidatus Microthrix filamentous bacteria and hindered settling velocity parameter values. While no direct association was observed between filamentous abundance and compression settling parameters, we propose linking the dynamic calibration of the compressive solid stress function to v0/rH. Notably, our results demonstrate, for the first time, the efficacy of dynamic calibration of SST models using the relative abundance of filamentous microbial predictors in a simulation model of the Kloten-Opfikon full-scale WRRF. Furthermore, besides Cand. Microthrix, Thiothrix is found to be a putative predictor for biomolecular SST calibration. These findings shed light on the potential of microbial communities to predict hindered settling velocity in WRRFs and offer valuable insights for improving wastewater treatment processes in the face of climate change challenges.

Diversity Analysis and Biocontrol Potential of Cultivatable Terrestrial Bacterial Streptomyces in Southern China

Streptomyces are filamentous bacteria that are extensively present in soil, play an important role in carbon cycling, and produce a large number of highly valuable secondary metabolites. In this study, total number of 411 isolates of Streptomyces were collected from ecologically similar habitats from 13 provinces in Southern China. They were clustered into 96 operational taxonomic units including eight potentially new species based on their 16S rDNA sequences. Phylogenetic analysis disclosed that the isolates with similar geographical distributions clustered together. Beta diversity of Streptomyces showed it manifests in a latitudinal diversity gradient (R2 = 0.3828, p = 0.0113). The beta diversity did not change significantly with geographic distance, and this could be due to the large longitudinal and relatively smaller latitudinal sampling range, as the phylogenetic clustering of regions with higher annual average temperature was analyzed with the nearest taxon index (R = −0.23, p = 0.045). Result of the Streptomyces biogeography evaluation shows the diversity of the genus is controlled by many of the same processes. Bioassay results disclosed that there were 27 isolates strongly antagonistic to plant pathogenic fungi and 71 isolates with strong nematocidal activity against pine wood nematode. Our results provide significant insights into the diversity and biocontrol potential of cultivatable Streptomyces in Southern China.

Low dietary fiber intake impairs small intestinal Th17 and intraepithelial T cell development over generations

Dietary fiber strongly impacts the microbiota. Here, we show that a low-fiber diet changes the small intestinal (SI) microbiota and impairs SI Th17, TCRαβ+CD8αβ+ and TCRαβ+CD8αα+ intraepithelial Tcell development. We restore Tcell development with dietary fiber supplementation, but this defect becomes persistent over generations with constant low-fiber diets. Offspring of low-fiber diet-fed mice have reduced SI Tcells even after receiving a fiber-rich diet due to loss of bacteria important for Tcell development. In these mice, only a microbiota transplant from a fiber-rich diet-fed mouse and a fiber-rich diet can restore Tcell development. Low-fiber diets reduce segmented filamentous bacteria (SFB) abundance, impairing its vertical transmission. SFB colonization and a fiber-rich diet partially restore Tcell development. Finally, we observe that low-fiber diet-induced Tcell defects render mice more susceptible to Citrobacter rodentium infection. Together, these results demonstrate the importance of fiber to microbiota vertical transmission and host immune system development.

Study on the formation process and mechanism of aerobic granular sludge in the sequencing batch biofilter granular reactor.

Sequencing batch biofilter granular reactor (SBBGR) is a promising wastewater treatment technology owing to its low sludge yield and good toxicity tolerance. However, little attention has been paid to the formation process and mechanism of aerobic granular sludge in SBBGR. This study systematically investigated the formation process and mechanism of aerobic granular sludge in an SBBGR to provide a theoretical basis for optimizing the culture of aerobic granular sludge. Aerobic granular sludge with good performance was successfully cultivated after 40 days of incubation using synthetic wastewater as feed: the mixed liquid suspended solids and mixed liquor volatile suspended solids increased from 3.85 and 1.85 g/L to 31.38 and 24.74 g/L respectively, and the COD, TN, and TP removal efficiencies were 91.21%, 84.99%, and 58.14%, respectively. The experimental results showed that Amoebacteria and Bacteroides played an important role in the formation of aerobic granular sludge, filamentous bacteria acted as a three-dimensional skeleton surrounded by filling bacilli and rod-shaped bacteria, and proteins played a dominant role in promoting granulation during the culture process.

Indications for a genetic basis for big bacteria and description of the giant cable bacterium Candidatus Electrothrix gigas sp. nov.

Bacterial cells can vary greatly in size, from a few hundred nanometers to hundreds of micrometers in diameter. Filamentous cable bacteria also display substantial size differences, with filament diameters ranging from 0.4 to 8 µm. We analyzed the genomes of cable bacterium filaments from 11 coastal environments of which the resulting 23 new genomes represent 10 novel species-level clades of Candidatus Electrothrix and two clades that putatively represent novel genus-level diversity. Fluorescence in situ hybridization with a species-level probe showed that large-sized cable bacteria belong to a novel species with the proposed name Ca. Electrothrix gigas. Comparative genome analysis suggests genes that play a role in the construction or functioning of large cable bacteria cells: the genomes of Ca. Electrothrix gigas encode a novel actin-like protein as well as a species-specific gene cluster encoding four putative pilin proteins and a putative type II secretion platform protein, which are not present in other cable bacteria. The novel actin-like protein was also found in a number of other giant bacteria, suggesting there could be a genetic basis for large cell size. This actin-like protein (denoted big bacteria protein, Bbp) may have a function analogous to other actin proteins in cell structure or intracellular transport. We contend that Bbp may help overcome the challenges of diffusion limitation and/or morphological complexity presented by the large cells of Ca. Electrothrix gigas and other giant bacteria. IMPORTANCE In this study, we substantially expand the known diversity of marine cable bacteria and describe cable bacteria with a large diameter as a novel species with the proposed name Candidatus Electrothrix gigas. In the genomes of this species, we identified a gene that encodes a novel actin-like protein [denoted big bacteria protein (Bbp)]. The bbp gene was also found in a number of other giant bacteria, predominantly affiliated to Desulfobacterota and Gammaproteobacteria, indicating that there may be a genetic basis for large cell size. Thus far, mostly structural adaptations of giant bacteria, vacuoles, and other inclusions or organelles have been observed, which are employed to overcome nutrient diffusion limitation in their environment. In analogy to other actin proteins, Bbp could fulfill a structural role in the cell or potentially facilitate intracellular transport.

Unique architecture of microbial snottites from a methane driven biofilm revealed by confocal microscopy.

Microbial biofilms occur in many shapes and different dimensions. In natural and semi-artificial caves they are forming pendulous structures of 10 cm and more. In this study a methane driven microbial community of a former medicinal spring was investigated. The habitat was completely covered by massive biofilms and snottites with a wobbly, gelatinous appearance. By using fluorescence techniques in combination with confocal laser scanning microscopy the architecture of these so far unknown snottites was examined. The imaging approaches applied comprised reflection of geogenic and cellular origin, possible autofluorescence, nucleic acid staining for bacterial cells, protein staining for bacteria and extracellular fine structures, calcofluor white for β 1 → 3, β 1 → 4 polysaccharide staining for possible fungi as well as lectin staining for the extracellular biofilm matrix glycoconjugates. The results showed a highly complex, intricate structure with voluminous, globular, and tube-like glycoconjugates of different dimensions and densities. In addition, filamentous bacteria seem to provide additional strength to the snottites. After screening with all commercially available lectins, by means of fluorescence lectin barcoding and subsequent fluorescence lectin binding analysis, the AAL, PNA, LEA, and Ban lectins identified α-Fuc, β-Gal, β-GlcNAc, and α-Man with α-Fuc as a major component. Examination of the outer boundary with fluorescent beads revealed a potential outer layer which could not be stained by any of the fluorescent probes applied. Finally, suggestions are made to further elucidate the characteristics of these unusual microbial biofilms in form of snottites. RESEARCH HIGHLIGHTS: The gelatinous snottites revealed at the microscale a highly complex structure not seen before. The extracellular matrix of the snottite biofilm was identified as clusters of different shape and density. The matrix of snottites was examined by taking advantage of 78 fluorescently-labeled lectins. The extracellular matrix glycoconjugates of snottites identified comprised: α-Fuc, β-Gal, β-GlcNAc, and α-Man. Probing the snottite outer surface indicated an additional unknown stratum.

Maduramycosis masquerading malignancy: A case report from rural oncology center

Mycetoma is a chronic granulomatous inflammation of the dermis and epidermis caused by filamentous bacteria in 60% of cases (actinomycetoma) or fungi (eumycetoma) in 40% of cases. A 45-year-old female presented with a left foot ulcer and gradually increasing swelling for 13 years in our department. The radiograph revealed multiple punch-out lytic areas in the tarsals with sclerosis and destruction of the calcaneum. The characteristic “dotin-circle” sign was appreciated on both ultrasound and magnetic resonance imaging. The causative organism and the radiological evaluation, especially bone involvement, are the most important factors that determine the choice of treatment. In the initial stages, chemotherapeutic drugs along with surgery are effective. The current concept is with treatment with a combination of drugs under the name of Welsh regimen.

Insights into the membrane fouling aggravation under polyethylene terephthalate microplastics contamination: From a biochemical point of view

This study evaluated the potential effects of polyethylene terephthalate microplastics (PET-MPs) on a membrane bioreactor. The results showed that 10–30 mg/L PET-MPs exposure showed a minor effect on reactor performances, while 50 mg/L PET-MPs significantly decreased the chemical oxygen demand and NH4+-N removal efficiencies. Long-term PET-MPs exposure resulted in sludge foaming, and significantly increased extracellular polymeric substances (EPS) contents from 463.08 ± 62.42 to 952.54 ± 23.67 mg/m2, which was the main factor in triggering severe membrane fouling. Excitation emission matrix and Fourier transform infrared spectroscopic analysis revealed significant changes in fluorescence properties and functional groups of EPS. Particularly, protein secondary structure analysis indicated that high abundant β-sheet facilitated the exposure of inner hydrophobic groups of bacterial cells and EPS, and consequently enhanced the interfacial interactions of foulants-foulants and membrane-foulants. Long-term PET-MPs exposure significantly shifted the microbial community structures. In particular, the abundances of foam-forming filamentous bacteria and quorum-sensing (QS) bacteria, such as Thiothrix, Kouleothrix and Aeromonas, were constantly increasing with the increasing PET-MPs concentration. Furthermore, PET-MPs exposure significantly up-regulated the abundances of genes encoding QS signaling molecules and exopolysaccharides, such as lasI, lsrA and algZ. Collectively, these findings suggested that PET-MPs exposure stimulated the excessive growth of fouling-causing bacteria, which contained more biofilm formation related genes, that consequently accelerated membrane fouling.

A cytochrome c551 mediates the cyclic electron transport chain of the anoxygenic phototrophic bacterium Roseiflexus castenholzii

Roseiflexus castenholzii is a gram-negative filamentous phototrophic bacterium that carries out anoxygenic photosynthesis through a cyclic electron transport chain (ETC). The ETC is composed of a reaction center (RC)–light-harvesting (LH) complex (rcRC–LH); an alternative complex III (rcACIII), which functionally replaces the cytochrome bc1/b6f complex; and the periplasmic electron acceptor auracyanin (rcAc). Although compositionally and structurally different from the bc1/b6f complex, rcACIII plays similar essential roles in oxidizing menaquinol and transferring electrons to the rcAc. However, rcACIII-mediated electron transfer (which includes both an intraprotein route and a downstream route) has not been clearly elucidated, nor have the details of cyclic ETC. Here, we identify a previously unknown monoheme cytochrome c (cyt c551) as a novel periplasmic electron acceptor of rcACIII. It reduces the light-excited rcRC–LH to complete a cyclic ETC. We also reveal the molecular mechanisms involved in the ETC using electron paramagnetic resonance (EPR), spectroelectrochemistry, and enzymatic and structural analyses. We find that electrons released from rcACIII-oxidized menaquinol are transferred to two alternative periplasmic electron acceptors (rcAc and cyt c551), which eventually reduce the rcRC to form the complete cyclic ETC. This work serves as a foundation for further studies of ACIII-mediated electron transfer in anoxygenic photosynthesis and broadens our understanding of the diversity and molecular evolution of prokaryotic ETCs.

Phage-antibiotic synergy: Cell filamentation is a key driver of successful phage predation.

Phages are promising tools to fight antibiotic-resistant bacteria, and as for now, phage therapy is essentially performed in combination with antibiotics. Interestingly, combined treatments including phages and a wide range of antibiotics lead to an increased bacterial killing, a phenomenon called phage-antibiotic synergy (PAS), suggesting that antibiotic-induced changes in bacterial physiology alter the dynamics of phage propagation. Using single-phage and single-cell techniques, each step of the lytic cycle of phage HK620 was studied in E. coli cultures treated with either ceftazidime, cephalexin or ciprofloxacin, three filamentation-inducing antibiotics. In the presence of sublethal doses of antibiotics, multiple stress tolerance and DNA repair pathways are triggered following activation of the SOS response. One of the most notable effects is the inhibition of bacterial division. As a result, a significant fraction of cells forms filaments that stop dividing but have higher rates of mutagenesis. Antibiotic-induced filaments become easy targets for phages due to their enlarged surface areas, as demonstrated by fluorescence microscopy and flow cytometry techniques. Adsorption, infection and lysis occur more often in filamentous cells compared to regular-sized bacteria. In addition, the reduction in bacterial numbers caused by impaired cell division may account for the faster elimination of bacteria during PAS. We developed a mathematical model to capture the interaction between sublethal doses of antibiotics and exposition to phages. This model shows that the induction of filamentation by sublethal doses of antibiotics can amplify the replication of phages and therefore yield PAS. We also use this model to study the consequences of PAS on the emergence of antibiotic resistance. A significant percentage of hyper-mutagenic filamentous bacteria are effectively killed by phages due to their increased susceptibility to infection. As a result, the addition of even a very low number of bacteriophages produced a strong reduction of the mutagenesis rate of the entire bacterial population. We confirm this prediction experimentally using reporters for bacterial DNA repair. Our work highlights the multiple benefits associated with the combination of sublethal doses of antibiotics with bacteriophages.

Morphological and physiological adaptations of psychrophilic Pseudarthrobacter psychrotolerans YJ56 under temperature stress

Both culture-independent and culture-dependent analyses using Nanopore-based 16S rRNA sequencing showed that short-term exposure of Antarctic soils to low temperature increased biomass with lower bacterial diversity and maintained high numbers of the phylum Proteobacteria, Firmicute, and Actinobacteria including Pseudarthrobacter species. The psychrophilic Pseudarthrobacter psychrotolerans YJ56 had superior growth at 13 °C, but could not grow at 30 °C, compared to other bacteria isolated from the same Antarctic soil. Unlike a single rod-shaped cell at 13 °C, strain YJ56 at 25 °C was morphologically shifted into a filamentous bacterium with several branches. Comparative genomics of strain YJ56 with other genera in the phylum Actinobacteria indicate remarkable copy numbers of rimJ genes that are possibly involved in dual functions, acetylation of ribosomal proteins, and stabilization of ribosomes by direct binding. Our proteomic data suggested that Actinobacteria cells experienced physiological stresses at 25 °C, showing the upregulation of chaperone proteins, GroEL and catalase, KatE. Level of proteins involved in the assembly of 50S ribosomal proteins and L29 in 50S ribosomal proteins increased at 13 °C, which suggested distinct roles of many ribosomal proteins under different conditions. Taken together, our data highlights the cellular filamentation and protein homeostasis of a psychrophilic YJ56 strain in coping with high-temperature stress.