Mechanism of Bacillus subtilis Y61 Promoting the Growth of Weissella: Metabolic Interaction Based on Secretion of Arginine and Isovaleric Acid

Exploring the Role of Azurin from the Endophytic Bacterium Pseudomonas sp. OHS18 Through the Phenotypic Characterization of a Δazu Mutant

Azurin is a promising antitumor agent that selectively enters cancer cells and inhibits tumor progression. It is also known to participate in cellular processes involving single-electron transfer, including protection against oxidative stress, anaerobic respiration, and denitrification. However, the physiological role of azurin remains poorly understood. In this work, a multifaceted phenotypic characterization of an azurin-deficient mutant (Δazu) of the plant endophytic bacterium Pseudomonas sp. OHS18 was performed, using complementary approaches and technologies. Deletion of the azu gene did not affect resistance to antibiotics, copper, or hydrogen peroxide, while nuclear magnetic resonance-based metabolomic analysis revealed that the Δazu strain was moderately impaired in maintaining metabolic homeostasis from the exponential to the stationary growth phase. Phenotype microarray analyses showed that the two strains exhibited largely similar metabolic and resistance profiles, except for bromosuccinic acid utilization, under which the Δazu strain displayed reduced growth. This phenotype was further associated with a reduced ability of the mutant to colonize Arabidopsis thaliana, suggesting a role for azurin in maintaining the plant–bacterium association. Overall, these findings provide new insights into the physiological role of azurin in environmental bacteria and suggest its involvement in bacterium–eukaryote interactions, thereby opening new perspectives for biotechnological and biomedical applications.

Transcriptomic Analysis Reveals the Time-Dependent Mechanism of Antifungal Activity in Bacillus velezensis GHZJ-1

Frequent outbreaks of bacterial and fungal diseases in aquaculture cause severe economic losses, making biological control using probiotics a crucial strategy. Bacillus velezensis synthesizes diverse antimicrobial secondary metabolites; however, its biocontrol potential is tightly regulated by environmental signals such as cultivation time. In this study, we investigated the effect of growing time on the antifungal activity of B. velezensis GHZJ-1, isolated from an aquatic environment. It was found that GHZJ-1 shows obvious antifungal activity against the aquatic pathogen Metschnikowia bicuspidata upon 48 h growth but no such activity for 24 h via the agar-diffusion method. We further compared the transcriptomes of GHZJ-1 cells collected at 24 h and 48 h through RNA-Seq. Our results revealed that compared with 24 h, 1821 genes were differentially expressed at 48 h, with 903 upregulated and 918 downregulated. Downregulated genes were enriched in primary metabolic pathways (e.g., ribosome assembly and carbon metabolism), whereas upregulated genes were enriched in secondary metabolite biosynthesis and transmembrane transport. Importantly, 35 upregulated genes directly associated with antimicrobial activity were identified, notably including the ones encoding core elements of a large polyketide synthase (e.g., pksN, log2FC = 2.24), the petrobactin siderophore system (highest log2FC = 3.39), and various antimicrobial peptide export systems. Furthermore, the degU gene was activated at 48 h. These data suggest that facing continuously increased environmental stress over time, GHZJ-1 undergoes global transcriptional reprogramming and resource reallocation, downregulating basal metabolism to construct a synergistic antagonistic system coupling chemical defense with nutritional competition. This study elucidates the time-dependent mechanism for antifungal activity in GHZJ-1, providing a molecular theoretical basis for its green biocontrol application in aquaculture diseases caused by fungi.

Discovery and Comprehensive Characterization of Pseudomonas sp. MUP55: Taxonomy, Massetolide-Mediated Biocontrol, and Regulatory and Antimicrobial Contributions of the pvf Cluster

Pseudomonas sp. MUP55, isolated from rainfall water in Western Australia, was characterized by polyphasic taxonomy and functional assays. Whole-genome and 16S rRNA phylogeny placed Pseudomonas sp. MUP55 in the Pseudomonas fluorescens species group. Massetolide A/D was identified as the leading candidate bioactive compound(s), consistent with its biosynthetic gene cluster, GNPS library matching, and loss of activity in regulatory mutants. The strain showed broad-spectrum antimicrobial activity against bacterial (Escherichia coli and Xanthomonas campestris) and fungal (Fusarium oxysporum and Rhizoctonia solani) plant pathogens. GacA regulates Massetolide production: a P58L mutation abolished synthesis and reduced biocontrol efficacy. Metabolomic and transcriptomic analysis of a ΔpvfC mutant revealed that the pvf cluster regulates specialized metabolism while also contributing to secreted growth-inhibitory activity. The pvf cluster differentially regulates dual siderophore systems and uncouples the co-regulated small RNAs rsmY and rsmZ in the Gac/Rsm cascade. Deletion of pvfC partially reduced the growth-inhibitory activity of Pseudomonas sp. MUP55 supernatants against bacterial pathogens, indicating that pvfC also influences secreted antimicrobial activity beyond its global regulatory role. These findings establish Pseudomonas sp. MUP55 as a taxonomically novel, mechanistically characterized biocontrol agent with potential for sustainable agriculture.

Isolation of a Novel Brevibacillus parabrevis PS12 Strain from Soil and Determination of Optimal Conditions for Arginase Production

       Soil-occupy Brevibacillus parabrevius PS12 species are known for their metabolically versatile and it is being discovered as source of natural enzymes valuable to industry. Arginase catalyzes the processing of L-arginine to L-ornithine and urea, it is the one that plays a significant role in nitrogen metabolism Finding novel bacterial strains from environmental sources that are capable of producing the arginase enzyme is crucial for expanding microbial resources for industrial and pharmaceutical use. Among the 20 isolates, one isolate was identified as Brevibacillus parabrevis PS12 (97% 16S rRNA similarity, GenBank accession no. (PX118439.1), representing the first report from Iraqi soil. Arginase activity reached 8.3 U/mg protein a peak in nutritional source with maltose as a arbone source  and casein as a Nitrogen source, the physical parameters also effect on enzyme specific activity  at 7.0 pH, 37°C, and 48 hours of incubation time with shaker incubator 150 rpm to ensure the homogeneity of all medium components and continuous aeration all these factors contributed to an increase in bacterial biomass which led to a rise in the specific activity of arginase.

Mechanism of Thermosonication in Inhibiting Spore of Heat-Resistant Bacillus subtilis via Metabolic Networks and Gene Regulation

Surfactin-like lipopeptides contribute to interference competition of Bacillus velezensis against the marine Flavobacteriaceae in phycosphere.

BACKGROUND The phycosphere is a nutrient-rich microenvironment surrounding phytoplankton cells and serves as a hotspot for microbial interactions by releasing phytoplankton-derived organic molecules to dynamically attract and support the colonization of heterotrophic bacteria. Although the taxonomic composition, metabolic profiles, and host-microbe interactions of phycosphere bacterial communities have been extensively characterized, the underlying mechanisms driving competition among these co-existing bacterial taxa remain poorly understood. RESULTS In this study, we demonstrate that Bacillus velezensis SPE2, a low-abundance isolate from the phycosphere of dinoflagellate, exhibits a wide degree of antagonistic activity against multiple marine Flavobacteriaceae strains, a dominant taxonomic group across the phycosphere of diverse phytoplankton species. Through an integrative approach combining genetics and metabolomics, we show that the antagonistic behavior of strain SPE2 is primarily mediated by the production of bioactive secondary metabolites. Activity-guided purification further leads to the identification of two antibacterial surfactin-like lipopeptides as key exometabolites responsible for these inhibitory effects. Mechanistically, these lipopeptides exert their antibacterial activity against Flavobacteriaceae species by disrupting the integrity of bacterial cell membranes. CONCLUSIONS Our findings reveal surfactin-like lipopeptides as key molecular mediators of bacterial interference competition, conferring a competitive strategy for Bacillus species to secure persistence in the phycosphere. Moreover, this work underscores phycosphere as a largely untapped ecological niche for discovering novel bioactive compounds with potential applications in pharmaceutical and biotechnological fields.