Effect of Metabolites Produced by Bacillus atrophaeus and Brevibacterium frigoritolerans Strains on Postharvest Biocontrol of Alternaria alternata in Tomato (Solanum lycopersicum L.)

Whole-Genome Sequencing of Peribacillus frigoritolerans Strain d21.2 Isolated in the Republic of Dagestan, Russia

Pesticide-free agriculture is a fundamental pillar of environmentally friendly agriculture. To this end, there is an active search for new bacterial strains capable of synthesizing secondary metabolites and toxins that protect crops from pathogens and pests. In this study, we isolated a novel strain d21.2 of Peribacillus frigoritolerans from a soil sample collected in the Republic of Dagestan, Russia. Leveraging several bioinformatic approaches on Illumina-based whole-genome assembly, we revealed that the strain harbors certain insecticidal loci (coding for putative homologs of Bmp and Vpa) and also contains multiple BGCs (biosynthetic gene clusters), including paeninodin, koranimine, schizokinen, and fengycin. In total, 21 BGCs were predicted as synthesizing metabolites with bactericidal and/or fungicidal effects. Importantly, by applying a re-scaffolding pipeline, we managed to robustly predict MGEs (mobile genetic elements) associated with BGCs, implying high genetic plasticity. In addition, the d21.2's genome was free from genes encoding for enteric toxins, implying its safety in use. A comparison with available genomes of the Peribacillus frigoritolerans strain revealed that the strain described here contains more functionally important loci than other members of the species. Therefore, strain d21.2 holds potential for use in agriculture due to the probable manifestation of bactericidal, fungicidal, growth-stimulating, and other useful properties. The assembled genome is available in the NCBI GeneBank under ASM4106054v1.

Exploration of the Biocontrol Activity of Bacillus atrophaeus Strain HF1 against Pear Valsa Canker Caused by Valsa pyri

Valsa pyri-induced pear Valsa canker is among the most prevalent diseases to impact pear quality and yields. Biocontrol strategies to control plant disease represent an attractive alternative to the application of fungicides. In this study, the potential utility of Bacillus atrophaeus strain HF1 was assessed as a biocontrol agent against pear Valsa canker. Strain HF1 suppressed V. pyri mycelium growth by 61.20% and induced the development of malformed hyphae. Both culture filtrate and volatile organic compounds (VOCs) derived from strain HF1 were able to antagonize V. pyri growth. Treatment with strain HF1-derived culture filtrate or VOCs also induced the destruction of hyphal cell membranes. Headspace mixtures prepared from strain HF1 were analyzed, leading to the identification of 27 potential VOCs. Of the thirteen pure chemicals tested, iberverin, hexanoic acid, and 2-methylvaleraldehyde exhibited the strongest antifungal effects on V. pyri, with respective EC50 values of 0.30, 6.65, and 74.07 μL L-1. Fumigation treatment of pear twigs with each of these three compounds was also sufficient to prevent the development of pear Valsa canker. As such, these results demonstrate that B. atrophaeus strain HF1 and the volatile compounds iberverin, hexanoic acid, and 2-methylvaleraldehyde exhibit promise as novel candidate biocontrol agents against pear Valsa canker.

Multimodal analysis of south-eastern Black Sea sediment bacterial population diversity

This study focused on marine sediments from the Black Sea, mainly due to bacterial diversity-induced public health / biotechnology application value. Sediment samples were gathered from 14 locations at differing depths across Turkish shores on a seasonal basis over 10 months, with bacterial identifications performed through using multimodal analytical platforms. Overall, 26 differing, predominantly Gram-positive (57.5 %) bacterial species were identified for this region, including Bacillaceae (50.0 %) and Pseudomonadaceae (15.0 %). The most dominant classes were identified as Bacilli (52.5 %) and Gammaproteobacteria (40.0 %). Ten isolates (25 %) to the species level and thirty-six isolates (90 %) to the genus level were identified using VITEK® MS and Bruker Microflex® LT/SH, in comparison to 16S rRNA sequencing results. Identified species - particularly, novel reported species - can contribute to the knowledge of microbial life dwelling upon sediments of the south-eastern regions of the Black Sea.