Aspergillus niger is one of the major pathogenic fungi causing postharvest grape decay. The development of antifungal agents is beneficial to reduce the loss of grapes during storage. The aim of this study was to investigate the antifungal mechanism of cyclosporin A (CsA). It was indicated that the rot development on grapes caused by A. niger was almost completely inhibited with CsA in vivo at a concentration of 200 mg/L. The transcriptomic analysis revealed that the expression levels of genes involved in rRNA processing and ribosome biogenesis were down-regulated, whereas those related to β-glucosidases and chitinases were up-regulated. The results implied that CsA may disturb rRNA and ribosome formation to obstruct protein synthesis, accelerate chitin and glucan degradation to destruct cell walls, and ultimately reduce postharvest decay caused by A. niger in grapes. This study evaluated the potential of CsA as a grape preservative and provided new insights into the mechanisms underlying the molecular response in A. niger with the treatment of CsA.

Two strains, designated NL03-T5^T and NL03-T5-1, were isolated from a soil sample collected from the Nanling National Forests, Guangdong Province, PR China. The two strains were Gram-stain-positive, aerobic, rod-shaped and had lophotrichous flagellation. Strain NL03-T5^T could secrete extracellular mucus whereas NL03-T5-1 could not. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the two strains belong to the genus Cohnella, were most closely related to Cohnella lupini LMG 27416^T (95.9% and 96.1% similarities), and both showed 94.0% similarity with Cohnella arctica NRRL B-59459^T, respectively. The two strains showed 99.8% 16S rRNA gene sequence similarity between them. The draft genome size of strain NL03-T5^T was 7.44 Mbp with a DNA G+C content of 49.2 mol%. The average nucleotide identities (ANI) and the digital DNA–DNA hybridization (dDDH) values between NL03-T5^T and NL03-T5-1 were 99.98% and 100%, indicating the two strains were of the same species. Additionally, the ANI and dDDH values between NL03-T5^T and C. lupini LMG 27416^T were 76.1% and 20.4%, respectively. The major cellular fatty acids of strain NL03-T5^T included anteiso-C_15:0 and iso-C_16:0. The major polar lipids and predominant respiratory quinone were diphosphatidylglycerol (DPG) and menaquinone-7 (MK-7). Based on phylogenetic analysis, phenotypic and chemotaxonomic characterization, genomic DNA G+C content, and ANI and dDDH values, strains NL03-T5^T and NL03-T5-1 represent novel species in the genus Cohnella, for which the name Cohnella silvisoli is proposed. The type strain is NL03-T5^T (=GDMCC 1.2294^T = JCM 34999^T). Furthermore, comparative genomics revealed that the genus Cohnella had an open pan-genome. The pan-genome of 29 Cohnella strains contained 41,356 gene families, and the number of strain-specific genes ranged from 6 to 1649. The results may explain the good adaptability of the Cohnella strains to different habitats at the genetic level.

Background: Plant growth-promoting rhizobacteria (PGPR) play essential roles in improving plant growth performance and enhancing plant disease resistance. Pseudomonas species are widely recognized as promising beneficial microorganisms owing to their excellent plant growth-promoting and biocontrol potential. Methods: Three bacterial strains, MBJ003, MBJ016 and MB1046, were isolated from potato and tomato rhizosphere soils collected in Guangdong Province, P.R. China. Taxonomic identification was performed based on morphological characteristics, physiological and biochemical profiles, as well as phylogenetic and whole-genome analyses. Genomic features, plant-growth promoting traits and antifungal activities against Geotrichum citri-aurantii were characterized, and the function of the type VI secretion system (T6SS) in strain MB1046 was explored. Results: Strain MBJ003 was identified as Pseudomonas paraeruginosa , MB1046 as Pseudomonas palmensis , and MBJ016 represents a novel Pseudomonas species. Whole-genome sequencing uncovered abundant and diverse secondary metabolite biosynthetic gene clusters (BGCs) underlying biocontrol capacity. Additionally, strain MB1046 harbours 17 type VI secretion system (T6SS) components. All three strains exhibited multiple plant-beneficial traits including phosphate solubilization, siderophore synthesis and IAA production, while strain MBJ003 additionally showed protease activity. The three strains displayed strong antagonism toward G. citri-aurantii . Their cell-free fermentation supernatants exerted antifungal effects, with MBJ003 showing the strongest inhibition. In vitro inoculation assays confirmed that these strains effectively control citrus postharvest disease caused by G. citri-aurantii . We further provided insights into the T6SS-mediated antagonism of MB1046 against G. citri-aurantii . Conclusion: This study systematically characterizes the plant-growth-promoting properties and antifungal mechanism of three Pseudomonas strains. These strains are valuable microbial candidates for developing biocontrol agents to manage crop postharvest diseases.