[Objective] The long-term intense continuous cropping and abuse of mineral fertilizers result in the degradation of upland red soil and the accumulation of soil-borne plant pathogens. Fungi are the microorganisms closely related to soil health in agroecosystems. We investigated the changes of soil fungal community to explore the effects of hairy vetch (Vicia villosa Roth L.) application on the agroecosystem with upland red soil.[Methods] We employed quantitative polymerase chain reaction (qPCR) and high-throughput sequencing (Illumina MiSeq) to investigate the responses of fungal communities to mineral fertilizer (hereinafter referred to as NPK) alone and mineral fertilizer combined with hairy vetch (hereinafter referred to as NPKG) in upland red soil.[Results] Compared with NPK, NPKG increased the soil fertility, peanut yield, and fungal abundance and decreased soil pH and soil fungal diversity. Different treatments significantly altered the soil fungal community composition. Compared with NPK, NPKG increased the relative abundance of saprophytic fungi by 37.42% and decreased the relative abundance ofCercospora arachidicola andLasidiplodia theobromae by 89.11% and 88.10%, respectively.[Conclusion] The application of hairy vetch significantly increased soil fertility, reduced the risk of peanut exposure to soil-borne diseases, and increased peanut yield in the upland red soil. Therefore, the application of hairy vetch was conducive to the sustainable development of upland red soil in southern China.

[Objective] To study the transcriptional regulation of type Ⅵ secretion system 1 (T6SS1) genes by QsvR inVibrio parahaemolyticus.[Methods] Total RNA was extracted from the wild type (WT) andqsvR mutant (ΔqsvR). Quantitative real-time PCR (qPCR) was employed to investigate the transcriptional regulation of target genes by QsvR. Primer extension was carried out to detect the transcription initiation site and core promoter for each target gene and calculate the transcriptional variations between WT and ΔqsvR. The regulatory DNA region of each target gene was cloned into the restriction endonuclease sites of pHRP309 harboring a promoterless genelacZ, and then each recombinant plasmid was transferred into WT and ΔqsvR, respectively. A β-Galactosidase Enzyme Assay System (Promega) was used to measure the β-galactosidase activity in cell lysates. The recombinant pHRP309 vector containing the regulatory DNA region of one of the target gene was transferred intoEscherichia coli 100λpir harboring an empty pBAD33 or pBAD33-qsvR to test whether QsvR can regulate the target genes in a heterologous host. The regulatory DNA region of each target gene was amplified by PCR, and His-QsvR was over-expressed and then purified under native conditions with nickel loaded HiTrap Chelating Sepharose columns (Amersham). Electrophoretic mobility shift assay (EMSA) was employed to determine the DNA-binding activity of His-QsvR to each target DNA fragmentin vitro.[Results] The mRNA levels of T6SS1-associated genes, VP1388 (the first gene of VP1388–1390 operon) andhcp1 (the first gene of VP1393–1406 operon), were significantly up-regulated in ΔqsvR relative to those in WT, indicating that QsvR activated the transcription of VP1388 andhcp1. Only one transcription initiation site was detected for VP1388 orhcp1, locating at 64 bp upstream of VP1388 and 62 bp upstream ofhcp1, respectively, and their transcriptional activities were all repressed by QsvR. QsvR repressed the promoter activities of VP1388 andhcp1 in bothV.parahaemolyticus andE.coli 100λpir. His-QsvR was able to bind to the regulatory DNA regions of VP1388 andhcp1.[Conclusion] QsvR directly repressed the transcription of T6SS1-associated operons, VP1388–1390 and VP1393–1406, inV.parahaemolyticus.

Fatty acids are not only the components of cell membrane but also the raw materials for the synthesis of bioactive molecules. Unsaturated fatty acids (UFAs) with low phase-transition temperatures are essential molecules for bacteria to regulate cell membrane fluidity. Therefore, the synthetic pathways of UFAs are key targets for the screening of antibacterial agents. Bacteria can adopt the anaerobic pathway to synthesize UFAs. For example,Escherichia coli, a model organism, synthesizes UFAsvia the classic FabA-FabB pathway. However, the anaerobic pathways for the synthesis of UFAs vary in different bacteria, and the catalytic enzymes are also different. Bacteria can synthesize UFAsvia aerobic pathways, in which fatty acid desaturase directly converts saturated fatty acids (SFAs) into UFAs. Different desaturases introduce double bond to form UFAs with different structures, which play roles in stress responses, pathogenicity and other aspects. Other enzymes involved in the synthesis of fatty acids can also participate in the synthesis of UFAs or regulation of different UFAs. Some bacteria can use monooxygenase to convert capryl-ACP (acyl carrier protein) in the fatty acid synthesis pathway intocis-3-decenyl ACP to synthesize UFAs. We comprehensively reviewed the research progress in the synthesis of UFAs in bacteria, aiming to provide theoretical support for deciphering the mechanism of bacterial synthesis of UFAs and developing the targeted antibacterial drugs.

Proper pH is crucial for the survival and functions of microorganisms, whether in the environment or within cells. Under acidic or alkaline stress, microorganisms have evolved diverse strategies, such as proton transport, production of acidic or alkaline substances, and cell membrane protection, to maintain intracellular pH homeostasis. Moreover, microorganisms have evolved the ability to actively change the extracellular pH. This article reviews the mechanisms by which microorganisms maintain intracellular pH homeostasis under acid or alkaline stress and alter extracellular pH. It aims to enhance our understanding of the interaction between microorganisms and the environment and provide a reference for further research on the synergistic mechanisms between microorganisms and the environment.

[Objective] This study aims to observe the changes of the fecal microbial communities in the dairy cows with subacute rumen acidosis (SARA) induced by a high-concentrate diet and modulated by the addition of vitamin E (VE). The potential effects on the metabolism of dairy cows were evaluated to provide data for exploring the physiological mechanisms of SARA.[Methods] Seven multiparous Holstein cows with rumen fistulas were selected for this trial which was carried out in three phases of 18 days each. The first phase was the control (CON) phase, with a concentrate-to-forage ratio of 50:50 in the diet (dry matter basis). The second phase was the induction (HG) phase, in which the forage was replaced with wheat flour at 15% of the diet (dry matter basis) to induce SARA. The third phase was the regulation (HGE) phase, in which VE was added at 12 000 IU/d/cow on the basis of the diet in the HG phase. The feces samples were collected on day 18 in each phase, and the microbial communities in the samples were examined.[Results] The fecal microbial community structure showed significant differences between three phases and the Shannon index in the HG phase was lower than that in the CON phase (P < 0.05). The HG phase had higher relative abundance ofProteobacteria andBlautia and lower relative abundance of unidentified_bacteria,Euryarchaeota,Desulfobacterota,Rikenellaceae_RC9_gut_group, andAlistipes than the CON phase (P < 0.05). The relative abundance ofBlautia in the HGE phase was higher than that in the HG phase (P < 0.05). The functional prediction results showed that SARA caused metabolic disorders in the dairy cows, while VE regulated the intestinal microbiota and health by improving the stability of microbial growth and promoting microbial reproduction.[Conclusion] The SARA induced by a high-concentrate diet led to reduced intestinal microbial diversity and metabolic disorders in dairy cows. VE can regulate intestinal health and maintain intestinal homeostasis by promoting the proliferation of beneficial intestinal microorganisms.

With the evolution of bacteria and the overuse of certain antibiotics, drug-resistant bacterial infections have emerged as a major public health challenge in the 21st century.Klebsiella pneumoniae, in particular, has aroused wide concern due to its drug-resistant nature. Bacteriophages have demonstrated the potential and advantages in treating bacterial infections caused by drug-resistant strains, while there are no clinical guidelines for phage therapy. Notably, even though a few successful cases of bacteriophage therapy have been documented in the treatment ofK.pneumoniae infections, bacteriophages are used in combination with antibiotics in most cases and the role bacteriophages play remains unclear. This article provides an overview of bacteriophage therapies forK.pneumoniae infections, including their characteristics and the factors influencing their efficacy. We compiled and analyzed data from available studies, with the intention of offering valuable insights for the application of bacteriophage therapy in combatingK.pneumoniae and other drug-resistant bacteria.

[Objective] To investigate the regulatory role of the transcription factor BldM in the morphological development and antibiotic synthesis ofStreptomyces pactum Act12, a biocontrol strain with multiple effects.[Methods] ThebldM-deleted mutant strain ∆bldM and thebldM-overexpressing mutant strain OE-bldM were constructed by genetic engineering. The scanning electron microscopy, antibacterial experiment, high performance liquid chromatography, and real-time quantitative PCR were employed to compare the morphological development, growth rate, oligomycin yield, and resistance to pathogens, respectively, between ∆bldM, OE-bldM, and the wild-type strain Act12.[Results] The sequencing results proved that ∆bldM and OE-bldM were successfully constructed. ∆bldM showed significantly reduced production of oligomycin D and was incapable of forming aerial hyphae. OE-bldM presented dense aerial hyphae and active sporulation. Compared with the wild type, OE-bldM showed an increase of 23% in the yield of oligomycin D and the up-regulation of 2–3 times in the transcriptional levels of the genes encoding oligomycin core synthetase. Moreover, the antimicrobial activity of OE-bldM remarkably enhanced.[Conclusion] The global transcriptional regulator BldM can not only affect the formation of aerial hyphae and sporulation but also participate in the positive regulation of oligomycin synthesis in Act12. The results of this study supplement the knowledge about the regulatory function of BldM and provide a reference for further research on the growth, metabolism, and regulation mechanism ofS.pactum Act12.

[Objective] Streptomyces is a genus of Gram-positive aerobic bacteria characterized by complex morphological differentiation and potent secondary metabolite-producing ability. SapB, a class Ⅲ lanthipeptide, promotes the morphological differentiation ofStreptomyces coelicolor, which suggests that SapB-like peptides might be developed as targets for engineering of morphological differentiation. In this study, we characterized the effects of SapB-like peptides on the morphological differentiation of multipleStreptomyces species, aiming to provide a theoretical basis for the engineering of these peptides.[Methods] Bioinformatics tools were used to analyze the gene clusters for the synthesis of SapB-like peptides in the genomes ofStreptomyces spp.. The plasmids for heterologous expression were constructed and introduced intoStreptomyces spp. through conjugation. The colony and mycelial morphology were compared to reveal the effects of these peptides on the morphological differentiation ofStreptomyces.[Results] SapB-like peptides promoted the differentiation ofStreptomyces from vegetative to aerial mycelia. Specifically, they increased the aerial mycelia and accelerated the differentiation, thus shortening the morphological differentiation cycle.[Conclusion] SapB-like peptides can help shorten the morphological differentiation cycle ofStreptomyces, demonstrating the potential for the morphological differentiation engineering ofStreptomyces.

[Objective] Cyanophages, the viruses specifically infecting cyanobacteria, are ubiquitous in water environments. They play a role in regulating the population dynamics and density of cyanobacteria and promote the biogeochemical cycling of the aquatic ecosystem. This study aims to isolate and identify a cyanophage.[Methods] A novel cyanophage Yong-L2-223 was isolated from fresh water samples with marineSynechococcus sp. PCC 7002 as the indicator host. The host range, genome sequence, open reading frames (ORFs), and phylogenetic relationship of Yong-L2-223 were studied.[Results] The host range tests against 31 strains of cyanobacteria showed that Yong-L2-223 could infect the indicator host PCC 7002 (Synechococcales) and two freshwater strainsMicrocystis viridis FACHB-1342 (Chroococcales) andAphanizomenon flos-aquae FACHB-1209 (Nostocales) from the Dianchi Lake. The infection of the cyanobacterial strains from both the seawater and freshwater samples indicated that Yong-L2-223 was a euryhaline cyanophage. Yong-L2-223 was myovirus-like, consisting of an icosahedral head (about 60 nm in diameter) and a contractile tail (about 136 nm in length). The genome (double-stranded DNA) of Yong-L2-223 had a length of 65 725 bp, with the G+C content of 58.6% and 100 ORFs. It was predicted to carry theCas4 gene, gene transfer factor (GTA) gene, auxiliary metabolic genes (AMGs), and a gene cluster for the synthesis of pre-Q₀. These genes may contribute to the adaptation and infection of the cyanophage in cyanobacteria of three orders. The pairwise sequence comparison (PASC) illustrated that the highest similarity sharing by cyanophage Yong-L2-223 and all the viruses in the current genome databases was only 3.78%, far below the genus boundary cut-off of 70% defined by the International Committee on Taxonomy of Viruses. In the phylogenetic tree based on the whole proteomes, Yong-L2-223 formed an independent branch, with long evolutionary distances from other phages.[Conclusion] Yong-L2-223 is a new genus of theCaudoviricetes class. For the first time, we used a marine cyanobacterial strain as the indicator host to isolate and obtain a novel cyanophage from freshwater, which broadened the understanding of cyanophages, enriched cyanophage genome database, and laid a foundation for the development of cyanophage resources.

[Objective] Bacillus thuringiensis (Bt), characterized by the massive production of insecticidal crystal proteins (ICPs) during sporulation, serves as the main strain resource for the commonly used and safe microbial insecticides. To further explore the mechanisms of sporulation and parasporal crystal formation and lay a theoretical foundation for the construction of efficient strains, we compared the transcriptomes of Bt at three important stages.[Methods] The transcriptomes of the hypervirulent strain Bt4.0718 at the middle vegetative growth stage (T1-10 h), the early sporulation stage (T2-20 h), and the late sporulation stage (T3-32 h) were compared. The representative differentially expressed genes (DEGs) were verified by real-time fluorescence quantitative PCR (qRT-PCR), and the phenotypes of the mutant strains with the knockout of specific functional genes were examined.[Results] The number of DEGs was 2 147 (T2/T1), 1 861 (T3/T1), and 1 708 (T3/T2), respectively. At T1, the medium was rich in nutrients, which served the sporulation and parasporal crystal formation. The high transcription levels ofkinA/D,spo0A/F, andsigE regulating sporulation played a role in the growth and development of the cells. The transcription of Cry1Ac, poly-hydroxybutyric acid (PHB), and hydroxybutanone (acetoin) were started at this time. The substantial formation of ICPs and spores occurred at T2 and T3, and the transcript levels of the regulatory genes were higher at T2 than those at T3. The genes associated with spore core/coat/cortex, germination protein, andspoII–spoVI began to be transcribed in large amounts at T2, with the highest levels among the three stages. The corresponding complex networks of carbohydrate, amino acid, and lipid metabolism, energy, nucleic acid, and peptide metabolism, secondary metabolite production, and environmental adaptation showed differences. In addition, as the physiological processes stimulated by nutrient signals, the two-component signal transduction system (TCS) and ABC transport system played an essential role in the process of sporulation and ICP transcription and expression, and their transcription levels were significantly different.[Conclusion] With the production of ICPs and sporulation, nutrients are gradually consumed, and the high expression ofsigB,sigW, andsigM contributed to the stability of cell wall and the resistance to environmental changes. Meanwhile, the small heat shock proteins Hsp20 and Hsp20B, as molecular chaperones, were also important for maintaining intracellular homeostasis and may facilitate the sporulation and ICP production.