Journal of General and Applied Microbiology最新文献

Sanghuangporus baumii polysaccharides (SBP) are recognized for their valuable pharmacological activities, driving increasing interest in their medicinal potential. However, the biosynthetic pathway of SBP remains incompletely characterized. Phosphoglucose isomerase (PGI), a key enzyme in carbohydrate metabolism, catalyzes the reversible isomerization between glucose-6-phosphate (G-6-P) and fructose-6-phosphate (F-6-P) and is hypothesized to regulate polysaccharide biosynthesis in this fungus. In this study, the pgi gene from S. baumii (sbpgi) was cloned and created sbpgi-silenced mutants using RNA interference (RNAi) to investigate its function. Silencing sbpgi resulted in an approximately 20% reduction in mycelial biomass but concurrently enhanced the production of exopolysaccharide (EPS) and intracellular polysaccharide (IPS) by approximately 2.0-fold and 1.9-fold after 9 days, respectively. Furthermore, suppression of sbpgi expression markedly decreased the content of cell wall β-1,3-glucan (by ~23%) while increasing chitin deposition by about 1.7-fold, leading to alterations in cell wall architecture, including thickness, and changes in stress tolerance. Transcriptional analysis revealed that sbpgi silencing significantly upregulated the expression of key genes in the polysaccharide biosynthetic pathway, including ugpg and pmm, highlighting the critical regulatory role of sbpgi in polysaccharide production. Our findings provide a foundation for metabolic engineering strategies to develop high-yielding strains for the industrial production of SBP.

Water is indispensable to life, yet some cyanobacteria inhabit hyper-arid deserts and withstand complete desiccation. However, the molecular mechanisms enabling such acclimation remain incompletely understood. In Anabaena sp. strain PCC 7120, the gene avaKa, which encodes a protein of unknown function, has been shown to be required for desiccation tolerance. Here, we characterized the avaKa disruptant DRavaKa under dehydration-related stress conditions. DRavaKa displayed hypersensitivity to EDTA, and transcripts of iron-deficiency-inducible genes (isiA1, isiB, furA, and sufB) were elevated even in the absence of EDTA. Whole-cell absorption spectra of DRavaKa revealed a blue shift of the chlorophyll absorption peak, a characteristic feature of iron-deficient cyanobacteria. In addition, the oxidative-stress-inducible gene trxA2 was likewise upregulated. These results indicate that AvaKa contributes to iron homeostasis and that iron deficiency-induced oxidative stress likely underlies the dehydration sensitivity of DRavaKa.

Plastics are indispensable in modern society, but their increasing production and disposal pose serious environmental challenges, including pollution and the depletion of non-renewable resources. Poly(ethylene furanoate) (PEF), a bio-based polyester composed of ethylene glycol and 2,5-furandicarboxylic acid (FDCA), is attracting attention as a sustainable alternative to poly(ethylene terephthalate) (PET). In this study, we developed a fully biotechnological upcycling system for PEF. Our approach involved enzymatic depolymerization of PEF to release FDCA, followed by microbial conversion of FDCA into polyhydroxyalkanoate (PHA), a biodegradable polyester. From soil samples enriched with FDCA as the sole carbon source, we isolated two bacterial strains: Pseudomonas sp. S8-1 and Caballeronia sp. S8-5. These strains produced medium-chain-length and short-chain-length PHAs, respectively, in defined medium containing FDCA. For enzymatic depolymerization, we employed the thermostable ICCG variant (F243I/D238C/S283C/Y127G) of leaf-branch compost cutinase, known for its high PET-degrading activity. The depolymerization of PET by this enzyme was enhanced by the addition of calcium carbonate (CaCO₃) powder to suppress acidification. Furthermore, the enzyme retained high activity even after partial purification by heat treatment at 60°C and efficiently depolymerized PEF as well. Finally, the PEF degradation solution was successfully utilized as a carbon source for PHA production by strain S8-5. These results demonstrate a proof-of-concept biorecycling system for PEF and represent a first step toward sustainable plastic management.

An efficient bacterial consortium (designated BPA-1), comprising Bacillus subtilis SX-6, Pseudomonas sp. SX-10, and Georgenia sp. SY-1, was successfully constructed for the decolorization of the azo dye Congo Red (CR). BPA-1 exhibited significant thermotolerance and heavy metal resistance, achieving over 90% CR decolorization within 60 h at 47°C under co-stress conditions with Zn²⁺, Mn²⁺, and Pb²⁺ (50 mg/L each). The consortium demonstrated broad substrate specificity, effectively decolorizing 12 structurally diverse azo dyes. Enzymatic assays revealed the involvement of laccase, manganese peroxidase, lignin peroxidase, and azoreductase in CR biodegradation. Metabolic pathway analysis indicated a three-stage degradation mechanism: (1) Asymmetric cleavage of azo bonds (-N=N-) generated 4,4'-diazaldenylbiphenyl and 4-amino-1-naphthalenesulfonic acid (Intermediate II); (2) Deamination converted Intermediate II to 3,4-dihydroxy-1-naphthalenesulfonic acid, followed by desulfurization to form naphthalene-1,2,3,4-tetraol; (3) Complete mineralization of intermediates occurred through subsequent oxidative steps. Notably, 4,4'-diazaldenylbiphenyl was further transformed into 4,4'-diaminobiphenyl, confirming the consortium's capacity for multi-step detoxification.

Bacillus thuringiensis (Bt) has broad spectrum multipotent functionalities for pest and disease suppression, and growth promotion (PGP) of plants. Therefore, potency of 27 rice rhizospheric and 2 commercial Bt isolates was assessed for biocidal and PGP traits. Functionally rhizospheric Bts were broadly superior than commercial Bts. Virulence of the Bts varied against rice leaf folder (LF, Cnaphalocrocis medinalis) and stripe stem borer (SSB, Chilo suppresalis) larvae in laboratory, net house and field tests. Drosophila diet (DD) incorporation, cut leaf and field assays proved virulence of 5-9 Bt isolates against LF larvae with LC₅₀s 1.99 - 6.31 x 10⁸, 2.18 x 10⁶ - 2.25 x 10⁹ and 3.16 x 10⁶ - 1.25 x 10⁹ bacteria-spore-crystal (BSC)/ml, respectively, and TB261 was most (LC₅₀s 2.18 x 10⁶ - 3.98 x 10⁸ BSC/ml) infective. DD and cut stem assays for SSB proved virulence of 5 and 6 Bts with LC₅₀s 9.20 x 10⁶ - 3.62 x 10⁸ and 9.21 x 10⁶- 3.24 x 10⁸ BSC/ml, respectively, and maximum (LC₅₀s 9.20 - 9.21 x 10⁸ BSC/ml) infectivity of TB263. Eight Bts inhibited 1-4 out of 7 rice pathogens and 16 Bts antagonized 1-4 out of 9 entomopathogenic fungi. Biocidal principles of the Bts were cell wall/membrane hydrolyzing exoenzymes, toxin/inhibitors and crystal toxins. Furthermore, the Bts were also inhibited by 3 insecticides and 2 fungicides. The Bts possessed 1-4 PGP and phytostimulation traits also. The potent rhizospheric Bt can be prospected for overall improvement/sustenance of rice.

Superoxide dismutases (SODs) play crucial roles in protecting cells against oxidative stress by catalyzing the dismutation of superoxide radicals. In Aspergillus nidulans, five putative SOD genes have been predicted in the genome; however, their comparative expression profiles and physiological functions remain largely uncharacterized. In this study, we analyzed the expression levels of all five SOD genes at different growth stages and examined the oxidative stress sensitivity of corresponding gene-disrupted strains. We found that sodA exhibited high and constitutive expression across all growth stages, while sodB was predominantly expressed in conidia (asexual spores). Disruption mutants of sodA and sodB showed increased sensitivity to oxidative agents, confirming their functional importance. Subcellular fractionation and SOD activity assays revealed that SodA was localized in the cytoplasm, whereas SodB was primarily localized in mitochondria. These results highlight the growth stage-specific expression and distinct cellular roles of SodA and SodB in A. nidulans, providing novel insights into the oxidative stress defense system in filamentous fungi.

Superoxide dismutases (SODs) play crucial roles in cellular oxidative stress defense. In Aspergillus nidulans, SodB is a mitochondria-localized SOD whose physiological function remains poorly understood. Here, we show that a ΔsodB mutant displays impaired growth on non-fermentable carbon sources including acetate, ethanol, threonine, and Tween 20/80, suggesting compromised mitochondrial function. Oxygen consumption assays using an extracellular oxygen consumption reagent revealed a ~50% reduction in respiratory activity in the ΔsodB strain compared to the wild type. When mitochondrial respiration was inhibited by Antimycin A or salicylhydroxamic acid, giant colony growth was equally suppressed across wild-type, ΔsodA, ΔsodB, and complemented strains. However, conidial production was significantly reduced in ΔsodB under Antimycin treatment, and morphological abnormalities in conidiophore heads were observed under this condition. These results indicate that SodB is not only involved in mitochondrial respiration but also required for maintaining normal sporulation under mitochondrial stress conditions. This study provides new insights into the role of mitochondrial ROS defense systems in filamentous fungal development.

At the 2025 Osaka/Kansai Expo, a bacterial-bioluminescence-based lighting system, called BIOLIGHT, was exhibited. It consists of 80 liters of liquid culture medium and produces enough brightness to illuminate a room. In this study, to make clear the relationship between the liquid culture thickness and the brightness using BIOLIGHT, the world's largest liquid culture aquarium of bioluminescent bacteria, we investigated the brightness of the bacterial liquid culture in relation to optical density (OD). The theoretical brightness of BIOLIGHT was calculated using the transmittance of the liquid culture at 475 nm (the peak luminescence wavelength) derived from the measured OD and was then compared with the brightness actually measured. The calculated (theoretical) brightness was lower than the measured one, suggesting that the light output of BIOLIGHT is influenced not only by cell-induced light shielding but also by another factor, presumably forward scattering. Additionally, depth-dependent brightness measurements showed that brightness became saturated at a liquid culture thickness greater than 7 cm. These findings will contribute to the design of future lighting solutions using bacterial bioluminescence.

Methionine gamma-lyase enzyme was isolated and purified from Mucor irregularis PQ344458 fungal isolates, that obtained from plant root, the isolates were identified through observation of their colony morphological features, implementation of PCR and DNA sequencing via sanger-chain termination approach, then data of DNA sequence alignment, phylogenetic tree, percent identity was generated. Through implementation of several stages that involved using of ion-exchange chromatography, gel-filtration chromatography, ammonium sulphate, enzyme isolation and purification stages were accomplished. The enzyme extract then, was analyzed for its protein content, specific activity and Impact of pH, temperature, inhibitors and activators on its kinetics. Additionally, MTT and DPPH radical scavenging assays were carried-out to reveal information about anti-cancer and anti-oxidant activities of methionine gamma-lyase enzyme. MTT assay results of %viable cells were 15% for HeLa cells and 6.6% for U937 cells at maximum concentration of the enzyme extract. Moreover, DPPH scavenging activity results were 82% at maximum concentration.

Serratia nuclease Nuc A is a non-specific nucleotide hydrolase that has been widely used in large-scale protein purification or eliminating nucleic acid contamination from purified proteins. To enhance the enzyme production, the Serratia nuclease gene was synthesized and expressed in Bacillus licheniformis 2709, a robust strain capable of secreting native and heterologous proteins selectively or non-selectively. To further increase the secretory expression level of the enzyme, different strong promoters and signal peptides were fused with the mature Nuc A-encoding gene at various genetic loci. The highest expression level of Nuc A was observed under the control of regulatory elements P_aprE, which occur naturally in B. licheniformis 2709 for the alkaline protease (AprE) expression. Through maximizing the number of copies of P_aprE-nucA expression cassette at different integration sites, the yield of nuclease Nuc A reached approximately 31954 U/mL after 60 hours of cultivation in shake flasks. The specific activity of the recombinant nuclease reached 1.58×107 U/mg, which is about 9 times higher than that expressed in Escherichia coli strain. Additionally, the recombinant Nuc A exhibited high catalytic activities in the pH range of 7-10. Furthermore, it was resistant to 0.2% SDS, 1.0 mM PMSF, and 0.4% Triton X-100. After 8 M Urea treatment, residual activity is measured. The high expression levels and positive characteristics of recombinant Nuc A provide an effective solution for large-scale production and industrial application of the nuclease.