Fems Microbiology Letters最新文献

Acinetobacter baumannii is one of the most prevalent causes of nosocomial infections worldwide. However, a paucity of information exists regarding the connection between metabolic capacity and in vivo bacterial fitness. Elevated lactate is a key marker of severe sepsis. We have previously shown that the putative A. baumannii lactate permease gene, lldP, is upregulated during in vivo infection. Here, we confirm that lldP expression is upregulated in three A. baumannii strains during a mammalian systemic infection. Utilising a transposon mutant disrupted for lldP in the contemporary clinical strain AB5075-UW, and a complemented strain, we confirmed its role in the in vitro utilisation of l-(+)-lactate. Furthermore, disruption of the lactate metabolism pathway resulted in reduced bacterial fitness during an in vivo systemic murine competition assay. The disruption of lldP had no impact on the susceptibility of this strain to complement mediated killing by healthy human serum. However, growth in biologically relevant concentrations of lactate observed during severe sepsis, led to bacterial tolerance to killing by healthy human blood, a phenotype that was abolished in the lldP mutant. This study highlights the importance of the lactate metabolism pathway for survival and growth of A. baumannii during infection.

Thioredoxin (Trx) is a disulfide-containing redox protein that functions as a disulfide oxidoreductase. Myxococcus xanthus contains five Trxs (Trx1-Trx5) and one Trx reductase (TrxR). Trxs typically have a CGPC active-site motif; however, M. xanthus Trxs have slightly different active-site sequences, with the exception of Trx4. The five Trxs of M. xanthus exhibited reduced activities against insulin, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), cystine, glutathione disulfide (GSSG), S-nitrosoglutathione (GSNO), and H2O2 in the presence of TrxR. Myxococcus xanthus adenylate kinase and serine/threonine phosphatase activities, which were increased by the addition of dithiothreitol, were activated by the addition of Trxs and TrxR. Among these, Trx1, which has a CAPC sequence in its active site, exhibited the highest reducing activity with the exception of GSNO. Myxococcus xanthus TrxR showed weak reducing activity towards DTNB, GSSG, GSNO, and H2O2, suggesting that it has broad substrate specificity, unlike previously reported low-molecular-weight TrxRs. TrxR reduced oxidized Trx1 as the best substrate, with a kcat/Km value of 0.253 min-1 µM-1, which was 10-28-fold higher than that of the other Trxs. These results suggest that all Trxs possess reducing activity and that Trx1 may be the most functional in M. xanthus because TrxR most efficiently reduces oxidized Trx1.

Pretreatment of lignocellulosic biomass produces growth inhibitory substances such as furfural which is toxic to microorganisms. Acinetobacter baylyi ADP1 cannot use furfural as a carbon source, instead it biotransforms this compound into difurfuryl ether using the reduced nicotinamide adenine dinucleotide (NADH)-dependent dehydrogenases AreB and FrmA during aerobic acetate catabolism. However, NADH consumption for furfural biotransformation compromises aerobic growth of A. baylyi ADP1. Depending on the growth phase, several genes related to acetate catabolism and oxidative phosphorylation changed their expression indicating that central metabolic pathways were affected by the presence of furfural. During the exponential growth phase, reactions involved in the formation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) (icd gene) and NADH (sfcA gene) were preferred when furfural was present. Therefore a higher NADH and NADPH production might support furfural biotransformation and biomass production, respectively. In contrast, in the stationary growth phase genes of the glyoxylate shunt were overexpressed probably to save carbon compounds for biomass formation, and only NADH regeneration was appreciated. Finally, disruption of the frmA or areB gene in A. baylyi ADP1 led to a decrease in growth adaptation and in the capacity to biotransform furfural. The characterization of this physiological behavior clarifies the impact of furfural in Acinetobacter metabolism.

Stenotrophomonas infections pose significant therapeutic challenges due to escalating resistance to antibiotics and chemotherapeutic agents. Phages offer a potential solution by virtue of their specific bacterial targeting capabilities. In this study, we isolated a new Stenotrophomonas bacteriophage, named BUCT627, from hospital sewage. Phage BUCT627 exhibited a 30-min latent period and demonstrated a burst size of 46 plaque forming unit (PFU)/cell. Remarkably, this phage displayed robust stability across a wide pH range (pH 3-13) and exhibited resilience under varying thermal conditions. The receptor of phage BUCT627 on Stenotrophomonas maltophilia No. 826 predominantly consist of surface proteins. The complete genome of phage BUCT627 is a 61 860-bp linear double-stranded DNA molecule with a GC content of 56.3%, and contained 99 open reading frames and two tRNAs. Notably, no antibiotic resistance, toxin, virulence-related genes, or lysogen-formation gene clusters was identified in BUCT627. Transmission electron microscopy and phylogeny analysis indicated that this phage was a new member within the Siphoviridae family. The results of this study will enhance our understanding of phage diversity and hold promise for the development of alternative therapeutic strategies against S. maltophilia infections.

Seasonal changes in the diversity of tea plant endophytic fungi and the effects of sample storage conditions on detection were analyzed. Tea leaves were collected from the Saitama Tea Research Institute in Japan during winter (January 2020) and summer (August 2020). The effects of storage temperature (5, 10, 20, 25, and 30°C) and durations (1, 2, 3, 4, 5, 6, and 7 days) on endophytic fungal diversity and community structure were investigated. In summer, storage period and temperature did not affect the fungal colonization rate, frequency, and composition. In winter, storage temperature and period significantly affected the endophytic community structure. Fungal diversity was higher in winter than in summer. Positive relationships between diversity index and storage temperature and period were observed in winter, whereas the opposite trend was observed in summer. Our findings provide insight into the ecology of foliar endophytes of tea plants and the importance of proper sample collection and storage for microbiome studies.

Enterococcus raffinosus, named by Collins et al. in 1989, is a cocci-shaped bacterium that typically appears in pairs or short chains. As a Gram-positive and non-motile bacterium, it grows at 10°C-45°C, exhibiting negative peroxidase activity [1]. It is a normal flora in the oropharynx and gastrointestinal tract of domestic cats [2] and can also be isolated from human rectal swabs [3], it belongs to the same genus Enterococcus as Enterococcus faecalis and Enterococcus faecium. Enterococcus faecalis and Enterococcus faecium constitute 90% of clinically isolated strains. However, the incidence of other enterococci, excluding E. faecalis and E. faecium, is on the rise [4]. In this case report, a patient with pediatric urinary tract infections caused by E. raffinosus was presented, and a summary of relevant literature was provided.

Short-term adaptation of the microbiota could promote nutrient degradation and the host health. While numerous studies are currently undertaking feeding trials using sustainable diets for the aquaculture industry, the extent to which the microbiota adapts to these novel diets is poorly described. The incorporation of carbohydrates (CHO) within a 100% plant-based diet could offer a novel, cost-effective energy source that is readily available, potentially replacing the protein component in the diets. In this study, we investigated the short-term (3 weeks) effects of a high CHO, 100% plant-based diet on the mucosal and digesta associated microbiota diversity and composition, as well as several metabolic parameters in rainbow trout. We highlighted that the mucosa is dominated by Mycoplasma (44.86%). While the diets did not have significant effects on the main phyla (Proteobacteria, Firmicutes, and Actinobacteria), after 3 weeks, a lower abundance of Bacillus genus, and higher abundances of four lactic-acid bacteria were demonstrated in digesta. In addition, no post-prandial hyperglycemia was observed with high carbohydrate intake. These results provide evidence for the rapid adaptation of the gut microbiota and host metabolism to high CHO in combination with 100% plant ingredients in rainbow trout.

With the growing threat of drug-resistant Acinetobacter baumannii, there is an urgent need to comprehensively understand the physiology of this nosocomial pathogen. As penicillin-binding proteins are attractive targets for antibacterial therapy, we have tried to explore the physiological roles of two putative DD-carboxypeptidases, viz., DacC and DacD, in A. baumannii. Surprisingly, the deletion of dacC resulted in a reduced growth rate, loss of rod-shaped morphology, reduction in biofilm-forming ability, and enhanced susceptibility towards beta-lactams. In contrast, the deletion of dacD had no such effect. Interestingly, ectopic expression of dacC restored the lost phenotypes. The ∆dacCD mutant showed properties similar to the ∆dacC mutant. Conversely, in vitro enzyme kinetics assessments reveal that DacD is a stronger DD-CPase than DacC. Finally, we conclude that DacC might have DD-CPase and beta-lactamase activities, whereas DacD is a strong DD-CPase.

Salmonella enterica (S. enterica) is the most common food and waterborne pathogen worldwide. The growing trend of antibiotic-resistant S. enterica poses severe healthcare threats. As an alternative antimicrobial agent, bacteriophage-encoded endolysins (endolysins) are a potential agent in controlling S. enterica infection. Endolysins are enzymes that particularly target the peptidoglycan layer of bacterial cells, leading to their rupture and destruction. However, the application of endolysins against Gram-negative bacteria is limited due to the presence of the outer membrane in the cell wall, which hinders the permeation of externally applied endolysins. This study aimed the prokaryotic expression system to produce the recombinant endolysin ENDO-1252, encoded by the Salmonella bacteriophage-1252 associated with S. Enteritidis. Subsequently, ENDO-1252 had strong lytic activity not only against S. Enteritidis but also against S. Typhimurium. In addition, ENDO-1252 showed optimal thermostability and lytic activity at 25°C with a pH of 7.0. In combination with 0.1 mM EDTA, the effect of 120 µg of ENDO-1252 for 6 hours exhibited the highest lytic activity, resulting in a reduction of 1.15 log or 92.87% on S. Enteritidis. These findings suggest that ENDO-1252 can be used as a potential and innovative antibacterial agent for controlling the growth of S. Enteritidis.

The extensive use of chemical pesticides, such as herbicides, has resulted in significant environmental pollution. Microbial degradation represents a crucial approach for managing this pesticide-associated pollution, with enrichment culturing serving as a method for isolating pesticide-degrading microorganisms. However, the efficiency of this strategy is limited, often yielding only a few isolated strains. In this study, a new mineral salt medium (MSM) was developed, and a high-throughput method was used for screening pendimethalin-degrading bacteria by measuring the bacterial growth in the MSM. The utilization of this method resulted in the isolation of 56 pendimethalin-degrading bacteria from approximately 2000 bacterial strains, including 37 Bacillus spp., 10 Alcaligenes spp., 5 Pseudomonas spp., and other 4 strains identified for the first time as pendimethalin-degrading strains. This method may hold promise not only for isolating bacterial strains capable of degrading other pesticides but also for facilitating the utilization of the substantial bacterial strains stored in bacterial banks.