Metal-Resistant PGPR Strain Azospirillum brasilense EMCC1454 Enhances Growth and Chromium Stress Tolerance of Chickpea (Cicer arietinum L.) by Modulating Redox Potential, Osmolytes, Antioxidants, and Stress-Related Gene Expression

Heavy metal stress, including from chromium, has detrimental effects on crop growth and yields worldwide. Plant growth-promoting rhizobacteria (PGPR) have demonstrated great efficiency in mitigating these adverse effects. The present study investigated the potential of the PGPR strain Azospirillum brasilense EMCC1454 as a useful bio-inoculant for boosting the growth, performance and chromium stress tolerance of chickpea (Cicer arietinum L.) plants exposed to varying levels of chromium stress (0, 130 and 260 µM K₂Cr₂O₇). The results revealed that A. brasilense EMCC1454 could tolerate chromium stress up to 260 µM and exhibited various plant growth-promoting (PGP) activities, including nitrogen fixation, phosphate solubilization, and generation of siderophore, trehalose, exopolysaccharide, ACC deaminase, indole acetic acid, and hydrolytic enzymes. Chromium stress doses induced the formation of PGP substances and antioxidants in A. brasilense EMCC1454. In addition, plant growth experiments showed that chromium stress significantly inhibited the growth, minerals acquisition, leaf relative water content, biosynthesis of photosynthetic pigments, gas exchange traits, and levels of phenolics and flavonoids of chickpea plants. Contrarily, it increased the concentrations of proline, glycine betaine, soluble sugars, proteins, oxidative stress markers, and enzymatic (CAT, APX, SOD, and POD) and non-enzymatic (ascorbic acid and glutathione) antioxidants in plants. On the other hand, A. brasilense EMCC1454 application alleviated oxidative stress markers and significantly boosted the growth traits, gas exchange characteristics, nutrient acquisition, osmolyte formation, and enzymatic and non-enzymatic antioxidants in chromium-stressed plants. Moreover, this bacterial inoculation upregulated the expression of genes related to stress tolerance (CAT, SOD, APX, CHS, DREB2A, CHI, and PAL). Overall, the current study demonstrated the effectiveness of A. brasilense EMCC1454 in enhancing plant growth and mitigating chromium toxicity impacts on chickpea plants grown under chromium stress circumstances by modulating the antioxidant machinery, photosynthesis, osmolyte production, and stress-related gene expression.

Biodegradation of low-density polyethylene plastic waste by a constructed tri-culture yeast consortium from wood-feeding termite: Degradation mechanism and pathway

Polyethylene (PE) is one of the most common synthetic polymers, and PE waste pollution has been an environmental and health concern for decades. Biodegradation is the most eco-friendly and effective approach for plastic waste management. Recently, an emphasis has been placed on novel symbiotic yeasts isolated from termite guts as promising microbiomes for multiple biotechnological applications. This study might be the first to explore the potential of a constructed tri-culture yeast consortium, designated as DYC, isolated from termites for the degradation of low-density polyethylene (LDPE). The yeast consortium DYC stands for the molecularly identified species Sterigmatomyces halophilus, Meyerozyma guilliermondii, and Meyerozyma caribbica. The LDPE-DYC consortium showed a high growth rate on UV-sterilized LDPE as a sole carbon source, resulting in a reduction in tensile strength (TS) of 63.4% and a net LDPE mass reduction of 33.2% compared to the individual yeasts. All yeasts, individually and in consortium, showed a high production rate for LDPE-degrading enzymes. The hypothetical LDPE biodegradation pathway that was proposed revealed the formation of several metabolites, including alkanes, aldehydes, ethanol, and fatty acids. This study emphasizes a novel concept for using LDPE-degrading yeasts from wood-feeding termites for plastic waste biodegradation.

Antifungal Activity of Bioactive Compounds Produced by the Endophytic Fungus Paecilomyces sp. (JN227071.1) against Rhizoctonia solani

Biologically active natural compounds are molecules produced by plants or plant-related microbes, such as endophytes. Many of these metabolites have a wide range of antimicrobial activities and other pharmaceutical properties. This study aimed to evaluate (in vitro) the antifungal activities of the secondary metabolites obtained from Paecilomyces sp. against the pathogenic fungus Rhizoctonia solani. The endophytic fungus Paecilomyces was isolated from Moringa oleifera leaves and cultured on potato dextrose broth for the production of the fungal metabolites. The activity of Paecilomyces filtrate against the radial growth of Rhizoctonia solani was tested by mixing the filtrate with potato dextrose agar medium at concentrations of 15%, 30%, 45%, and 60%, for which the percentages of inhibition of the radial growth were 37.5, 50, 52.5, and 56.25%, respectively. The dual culture method was conducted on PDA medium to observe the antagonistic nature of the antibiotic impacts of Paecilomyces sp. towards the pathogenic fungus. The strength of the antagonistic impacts was manifested by a 76.25% inhibition rate, on a scale of 4 antagonistic levels. Ethyl acetate extract of Paecilomyces sp. was obtained by liquid-liquid partition of the broth containing the fungus. Gas chromatography-mass spectrometry (GC-MS) analysis identified the presence of important chemical components e.g., (E) 9, cis-13-Octadecenoic acid, methyl ester (48.607), 1-Heptacosanol, 1-Nonadecene, Cyclotetracosane (5.979), 1,2-Benzenedicarboxylic acid, butyl 2-methylpropyl ester, di-sec-butyl phthalate (3.829), 1-Nonadecene, n-Nonadecanol-1, Behenic alcohol (3.298), n-Heptadecanol-1, 1-hexadecanol, n-Pentadecanol (2.962), Dodecanoic acid (2.849), 2,3-Dihydroxypropyl ester, oleic acid, 9-Octadecenal, and (Z)-(2.730). These results suggest that secondary metabolites of the endophytic Paecilomyces possess antifungal properties and could potentially be utilized in various applications, such as environmental protection and medicine.

Streptomyces rochei MS-37 as a Novel Marine Actinobacterium for Green Biosynthesis of Silver Nanoparticles and Their Biomedical Applications

Periodontitis, as one of the most common diseases on a global scale, is a public health concern. Microbial resistance to currently available antimicrobial agents is becoming a growing issue in periodontal treatment. As a result, it is critical to develop effective and environmentally friendly biomedical approaches to overcome such challenges. The investigation of Streptomyces rochei MS-37's performance may be the first of its kind as a novel marine actinobacterium for the green biosynthesis of silver nanoparticles (SNPs) and potentials as antibacterial, anti-inflammatory, antibiofilm, and antioxidant candidates suppressing membrane-associated dental infections. Streptomyces rochei MS-37, a new marine actinobacterial strain, was used in this study for the biosynthesis of silver nanoparticles for various biomedical applications. Surface plasmon resonance spectroscopy showed a peak at 429 nm for the SNPs. The SNPs were spherical, tiny (average 23.2 nm by TEM, 59.4 nm by DLS), very stable (-26 mV), and contained capping agents. The minimum inhibitory concentrations of the SNPs that showed potential antibacterial action ranged from 8 to 128 µg/mL. Periodontal pathogens were used to perform qualitative evaluations of microbial adhesion and bacterial penetration through guided tissue regeneration membranes. The findings suggested that the presence of the SNPs could aid in the suppression of membrane-associated infection. Furthermore, when the anti-inflammatory action of the SNPs was tested using nitric oxide radical scavenging capacity and protein denaturation inhibition, it was discovered that the SNPs were extremely efficient at scavenging nitric oxide free radicals and had a strong anti-denaturation impact. The SNPs were found to be more cytotoxic to CAL27 than to human peripheral blood mononuclear cells (PBMCs), with IC50 values of 81.16 µg/mL in PBMCs and 34.03 µg/mL in CAL27. This study's findings open a new avenue for using marine actinobacteria for silver nanoparticle biosynthesis, which holds great promise for a variety of biomedical applications, in particular periodontal treatment.