Fems Microbiology Letters最新文献

Azospirillum brasilense is a plant growth beneficial rhizobacterium (PGBR) that is used as an inoculant to enhance root architecture in grassland and crop plants. The intent of our study was to develop A. brasilense into a probiotic inoculant for peas and supplement with a seedling exudate compound, to be used together or separately. As an initial characterization of the association of A. brasilense with pea roots, we performed several pea growth experiments. Azospirillum brasilense Sp7T increased the lengths of the five longest lateral roots from each plant by 63.6% and the top 10 lateral roots across 14 plants by 30%, an effect that was abolished in an rpoN mutant and a ΔcheA1/cheA4 mutant. Azospirillum brasilense Cd increased the number of lateral roots by 76%. We detected colonization by this PGBR within the epiphytic root microbiome. To identify a pea seedling exudate compound capable of enhancing lateral pea roots, we tested 15 such compounds. Cytidine was the only one that increased the number of lateral roots, by approximately two-fold, an effect that did not require A. brasilense. We conclude that both A. brasilense and cytidine might be suitable as supplements to enhance lateral roots of pea plants.

Plant-based beverages are often fortified with different vitamins, especially B-vitamins, as the raw materials used for their production have a low content of these. Recently, we reported a simple and natural approach for obtaining vitamin B2 (riboflavin) secreting derivatives of the lactic acid bacterium (LAB) Lactococcus lactis, based on the observation that riboflavin can alleviate heat-induced oxidative stress. Here, we explore the potential of these strains for enriching plant-based beverages based on soy and oats, with riboflavin. Three riboflavin producing L. lactis strains were selected for the study: ER10, ALE13, and LDH13, where the latter is a lactate dehydrogenase-deficient derivative of ALE13. We found that ER10 produced more than 50 % more riboflavin in soy milk than ALE13 under static conditions (i.e. with no active aeration). Aerated culturing, in general, increased riboflavin production, especially for LDH13. The protein in oat milk is mostly insoluble and thus unavailable for the L. lactis strains used. To address this, oat milk was treated with food grade proteases, Alcalase® and Flavourzyme®, generating soluble peptides. When LDH13 was grown in the enzymatically treated oat milk with aeration, this resulted in a 600 % increase in riboflavin content (∼6 mg/L), demonstrating that the bioavailability of amino acids limits riboflavin production in oat milk. Here, we found that arginine played a special role in riboflavin production. By supplementing enzymatically treated oat milk with arginine, the riboflavin content could be further increased to 8 mg/L.

Bacterial biofilms mediate chronic and recurrent bacterial infections that are extremely difficult to treat by currently available standards of care. In nature, these encased bacterial communities are typically comprised of more than one genus or species. Specifically, in the airway, nontypeable Haemophilus influenzae (NTHI) predominates and is commonly isolated with one or more of the following co-pathogens with which it forms unique relationships: methicillin-resistant Staphylococcus aureus, Burkholderia cenocepacia, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Moraxella catarrhalis. We recently showed that dual-genera biofilms comprised of NTHI plus a co-pathogen are disrupted when the biofilm matrix is destabilized by a pathogen-directed strategy that uses a humanized monoclonal antibody directed against the protective domains of bacterial DNABII proteins found at vertices of crossed strands of eDNA within the biofilm matrix. We also recently showed that a peptide synthesized from the host innate immune effector High Mobility Group Box 1 (HMGB1), called mB Box-97syn, competitively inhibits binding of the bacterial DNABII proteins to eDNA, which thereby also destabilizes single-species biofilms to release biofilm-resident bacteria into a transient yet highly vulnerable state that is more effectively cleared by the host innate immune system and/or antibiotics. Here, we expanded upon these studies to assess the ability of host-augmenting mB Box-97syn to both disrupt two-genera biofilms formed by NTHI plus a common co-pathogen, and prevent their formation. Disruption of established two-genera biofilms ranged from 57% to 88%, whereas prevention of two-genera biofilm formation ranged from 65% to 80% (P = .002 to P < .0001). The sobering recalcitrance of chronic and recurrent respiratory tract infections, combined with growing global concern of antimicrobial resistance (AMR), demands development of more effective management and prevention options. Ideally, novel treatment strategies would both target the pathogens and augment the host's natural abilities to eradicate them. Herein, we provide additional data to support continued development of the latter concept via demonstration of mB Box-97syn's efficacy against polymicrobial biofilms.

The responses of bacterial communities to changing environmental conditions are manifold but can include structural as well as functional alterations depending on the environmental stressors and toxic chemicals they are exposed to (e.g. pharmaceuticals, personal care products, pesticides, and industrial chemicals). In this study, environmental DNA was extracted from surface water samples collected from four small rivers in the Lake Victoria South Basin (Western Kenya) to (i) evaluate whether alpha- and beta-diversity change in dependency of land-use types, (ii) identify the environmental variables that explain alterations in community structure, (iii) qualitatively and quantitatively assess the consequences of antimicrobial stress on bacterial communities, and (iv) evaluate bacterial functional changes related to the degradation of organic chemicals. Our findings suggest that bacterial community composition is a more sensitive indicator to reflect the impact of chemical pollution derived from different types of land use compared to alpha-diversity. Nutrients and stress from chemical pollution were the variables explaining the dissimilarities between bacterial communities in small, forested, urbanised, and agricultural rivers. Furthermore, an assessment of potential ecological functions associated with the biodegradation of toxic chemicals unveiled a season-specific decline in bacterial degradation potential in all four rivers.

Listeria monocytogenes is a Gram-positive facultative intracellular bacterium that is ubiquitous in nature and the causative agent of listeriosis. The outbreak-derived serotype 4b strain L. monocytogenes strain WS1, sequence type (ST) 558, sublineage (SL) 558, was previously found to have unusual pathogenicity, with ability to cause fetal damage in the first trimester of pregnancy. Search of the WS1 genome for novel and unique genomic features identified a putative lantibiotic island on the chromosome of WS1 and all tested strains of SL558 and two other putative emerging serotype 4b clones, clonal complex 554 (SL554 and SL555) and ST782 (SL782), but absent from all other major clones of L. monocytogenes. The island was deleted from four strains, including two each of ST558 and ST554. The deletions did not impact virulence in a Galleria mellonella model but consistently resulted in reduced hemolytic activity. In addition, we noted strain-dependent impacts on biofilm formation. Additional studies will be necessary to further elucidate the roles of this genomic island in the adaptive physiology and virulence of L. monocytogenes.

Actinobacillus seminis is a causative agent of epididymitis, infertility, and sterility in sexually mature ruminants. Previous studies suggest that sex hormones regulate the expression of A. seminis virulence factors, promote its growth, and support adhesin expression and biofilm formation; however, the effects of these hormones on protease expression are unknown. The effects of testosterone (1-5 ng/ml) and estradiol (5-25 pg/ml) were evaluated on the A. seminis protease expression. Zymograms revealed that both hormones enhanced the secretion of a 50 kDa metalloprotease and a 65 kDa serine protease. The 65 kDa serine protease showed optimal activity at a pH of 6-8, was stable at temperatures up to 70°C, and hydrolyzed bovine hemoglobin and casein; interestingly, this hemoglobin protease was expressed after treatment with sex steroid hormones but not in the presence of catecholamines. This serine-protease presents identity with two A. seminis serine proteases of 50 kDa. The metalloprotease has previously been shown to hydrolyze bovine IgG and fibrinogen and presented identity with a carboxy-terminal protease. Both proteases showed immune cross-reactivity with hyperimmune sera against metalloproteases from A. seminis and Actinobacillus pleuropneumoniae, and with serum against a Mannheimia haemolytica serine protease. Our results suggest that hormones affect the expression of different A. seminis virulence factors, such as proteases, and may play a key role in bacterial pathogenesis.

This study investigated the antibiofilm effects of Clitoria ternatea flowers anthocyanin fraction (AF) on Streptococcus mutans, Actinomyces viscosus, and Aggregatibacter actinomycetemcomitans. AF was obtained using column chromatography, and liquid chromatography-mass spectrometry was employed for its characterization and identification. The crystal violet assay and scanning electron microscopy analysis revealed significant inhibition of early biofilm formation and destruction of preformed biofilms after AF treatment (0.94-15 mg ml-1). Antiadhesion assay on acrylic teeth demonstrated that AF effectively hampered sucrose dependent and independent attachment. Importantly, growth curve and pH drop assays showed that AF inhibited pH reduction for all bacteria tested without hindering bacterial growth. Furthermore, the tetrazolium-based cytotoxicity assay indicated no toxicity towards normal human gingival fibroblasts at 0.78-12.5 mg ml-1. These findings suggest C. ternatea anthocyanins are promising antibiofilm agents for oral biofilm control, acting during both initial formation and on mature biofilms.

Arbuscular mycorrhizal (AM) fungi are fundamental to planetary health, enhancing plant nutrient uptake, stabilizing soils, and supporting biodiversity. Due to their prevalence and ecological importance, AM fungi are critical to achieving the environmental targets within the United Nations (UN) Sustainability Development Goals (SDGs) framework, including SDG 15: Life on Land. Despite these fungi engaging in the most widespread and ancient plant-microbe symbiosis, many fundamental aspects of the biogeography of AM fungi remain poorly resolved. This limits our ability to understand and document these fungal species' contributions to preserving terrestrial life on Earth. Using the largest global dataset of AM fungal eDNA sequences, we highlight that > 70% of ecoregions have no available data generated from soil using AM fungal specific metabarcoding. Drawing attention to these severe data gaps can optimize future sampling efforts in key habitats. Filling these gaps and developing a more complete picture on the biogeographic distributions of AM fungal species will help to clarify their contributions to environmental targets.

Taniborbactam (TAN) is an investigational β-lactamase inhibitor in clinical development combined with cefepime for the treatment of bacterial infections caused by broad-spectrum β-lactamase-expressing bacteria. Its spectrum of inhibition encompasses all classes of β-lactamases, including clinically important metallo-β-lactamases (MBLs) NDM-1 and VIM-2. However, TAN lacks a significant inhibition of imipenemase-type β-lactamases. Rare TAN-resistant New Delhi metallo-β-lactamase (NDM) or Verona integron-encoded metallo-β-lactamase (VIM) variants (namely NDM-9, NDM-30, and VIM-83) have been identified. The NitroSpeed Taniborbactam NP test was developed to rapidly assess the β-lactamase inhibitory activity of TAN against various β-lactamases, particularly serving as an efficient tool for identifying compounds with potential activity against different types of MBLs. The test is based on the hydrolysis of (i) nitrocefin (to determine the presence or absence of β-lactamase), (ii) ertapenem (to confirm the presence or the absence of carbapenemase), and (iii) TAN (to assess whether the carbapenemase is inhibited by TAN). The test was validated using a collection of 134 genetically characterized clinical isolates (103 Enterobacterales and 31 Pseudomonas aeruginosa). The NitroSpeed Taniborbactam NP test is simple, easy to perform, and provides results within ≤15 min. When evaluated against a broad set of β-lactamases, the test demonstrated 100% sensitivity, specificity, and accuracy.

Nitrogen is important for fungal growth and development, and the GATA transcription factor AreA has been widely studied as a key regulator of nitrogen catabolite repression (NCR) in many fungi. However, AreB, another GATA transcription factor in the NCR pathway, remains less studied, and its role in Aspergillus flavus is still unclear. In this study, we characterized areB in A. flavus and investigated its role in regulating nitrogen utilization, fungal growth, and aflatoxin production. The areB gene produces three transcripts, with areB-α being the most abundantly expressed, particularly under nitrogen-limited conditions. Gene expression analysis via qPCR confirmed that areB acts as a negative regulator of NCR, as its deletion led to the upregulation of NCR-related genes under nitrogen-limiting conditions. Gene function analysis of areB revealed that its deletion impaired hyphal growth, reduced conidia production, and delayed conidial germination. Additionally, deletion of areB led to increased aflatoxin production, particularly under less favorable nitrogen sources, while overexpression of areB reduced aflatoxin levels. Furthermore, areB influenced sclerotia formation in a nitrogen-source-dependent manner. These findings reveal the multifaceted role of areB in nitrogen regulation, fungal development, and secondary metabolism, offering insights for controlling aflatoxin contamination and fungal growth.