Detection and evaluation of volatile and non-volatile antifungal compounds produced by Bacillus spp. strains

Genomic Insights into the Bactericidal and Fungicidal Potential of Bacillus mycoides b12.3 Isolated in the Soil of Olkhon Island in Lake Baikal, Russia

The dispersal of plant pathogens is a threat to the global economy and food industry which necessitates the need to discover efficient biocontrol agents such as bacteria, fungi, etc., inhibiting them. Here, we describe the Bacillus mycoides strain b12.3 isolated from the soil of Olkhon Island in Lake Baikal, Russia. By applying the co-cultivation technique, we found that the strain inhibits the growth of plant pathogens, such as the bacteria Xanthomonas campestris, Clavibacter michiganensis, and Pectobacterium atrospecticum, as well as the fungus Alternaria solani. To elucidate the genomic fundament explaining these activities, we leveraged next-generation whole-genome sequencing and obtained a high-quality assembly based on short reads. The isolate bore seven known BGCs (biosynthetic gene clusters), including those responsible for producing bacillibactin, fengycin, and petrobactin. Moreover, the genome contained insecticidal genes encoding for App4Aa1, Tpp78Ba1, and Spp1Aa1 toxins, thus implicating possible pesticidal potential. We compared the genome with the 50 closest assemblies and found that b12.3 is enriched with BGCs. The genomic analysis also revealed that genomic architecture corresponds to the experimentally observed activity spectrum implying that the combination of produced secondary metabolites delineates the range of inhibited phytopathogens Therefore, this study deepens our knowledge of the biology and ecology of B. mycoides residing in the Lake Baikal region.

Isolation of a novel Bacillus subtilis HF1 strain that is rich in lipopeptide homologs and has strong effects on the resistance of plant fungi and growth improvement of broilers

Bacillus subtilis is an important probiotic microorganism that secretes a variety of antimicrobial compounds, including lipopeptides, which are a class of small molecule peptides with important application value in the fields of feed additives, food, biopesticides, biofertilizers, medicine and the biological control of plant diseases. In this study, we isolated a novel B. subtilis HF1 strain that is rich in lipopeptide components and homologs, has a strong antagonistic effect on a variety of plant fungi, and is highly efficient in promoting the growth of broilers. The live B. subtilis HF1 and its fermentation broth without cells showed significant inhibitory effects on 20 species of plant fungi. The crude extracts of lipopeptides in the fermentation supernatant of B. subtilis HF1 were obtained by combining acid precipitation and methanol extraction, and the lipopeptide compositions were analyzed by ultrahigh-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The results showed that HF1 could produce 11 homologs of surfactin and 13 homologs of fengycin. Among the fengycin homologs, C13-C19 fengycin A and C15-C17 fengycin B were identified; among the surfactin homologs, C11-C17 surfactin A and C13-C16 surfactin B were characterized. C13 fengycin A, C11 surfactin A and C17 surfactin A were reported for the first time, and their functions are worthy of further study. In addition, we found that HF1 fermentation broth with and without live cells could be used as a feed additive to promote the growth of broilers by significantly increasing body weight up to 15.84%. HF1 could be a prospective strain for developing a biocontrol agent for plant fungal diseases and an efficient feed additive for green agriculture.

Chemical and genetic characterization of lipopeptides from Bacillus velezensis and Paenibacillus ottowii with activity against Fusarium verticillioides

Introduction

The fungus Fusarium verticillioides significantly threatens maize crops in tropical soils. In light of this, biological control has emerged as a promising strategy to reduce fungicide costs and environmental risks. In this study, we aimed to test the antifungal activity of cell-free supernatant (CFS) from three Bacillus velezensis (CT02, IM14, and LIS05) and one Paenibacillus ottowii (LIS04) against F. verticillioides, thereby contributing to the development of effective biocontrol measures.

Methods

The research employed a comprehensive approach. The antifungal activity of the bacterial strains was tested using cell-free supernatant (CFS) from three Bacillus velezensis (CT02, IM14, and LIS05) and one Paenibacillus ottowii (LIS04). The UPLC-MS evaluated the CFS to identify the main bioactive molecules involved in the inhibitory effect on F. verticillioides. Scanning electron microscopy (SEM) was used to assess the impact of CFS on spores and hyphae, and genome sequencing was conducted to identify the genes involved in biological control. These robust methodologies ensure the reliability and validate our findings.

Results

The CFS of the four strains demonstrated significant inhibition of fungal growth. The UPLC-MS analysis revealed the presence of lipopeptides with antifungal activity, including surfactin and fengycins A and B expressed by the three strains of Bacillus velezensis and iturin A expressed by strains LIS05 and IM14. For Paenibacillus ottowii, fusaricidins, ABCDE, and five previously unreported lipopeptides were detected. Scanning electron microscopy (SEM) showed that treatments with CFS led to significant distortion and breakage of the F. verticillioides hyphae, in addition to the formation of cavities in the membrane. Genome mining confirmed the presence of genes coding for the lipopeptides identified by UPLC-MS, including the gene for iturin in CTO2. Genomic sequencing revealed that CT02, IM14, and LIS05 belong to different strains of Bacillus velezensis, and LIS04 belongs to Paenibacillus ottowii, a species recently described.

Discussion

The four bacterial strains, including three novel strains identified as Bacillus velezensis and one as the recently described species Paenibacillus ottowii, demonstrate significant potential as biocontrol agents for managing fungal disease. This finding underscores the novelty and potential impact of our research.

Genomic and biological control of Sclerotinia sclerotiorum using an extracellular extract from Bacillus velezensis 20507

Introduction

Sclerotinia sclerotiorum is a known pathogen that harms crops and vegetables. Unfortunately, there is a lack of effective biological control measures for this pathogen. Bacillus velezensis 20507 has a strong antagonistic effect on S. Sclerotiorum; however, the biological basis of its antifungal effect is not fully understood.

Methods

In this study, the broad-spectrum antagonistic microorganisms of B. velezensis 20507 were investigated, and the active antifungal ingredients in this strain were isolated, purified, identified and thermal stability experiments were carried out to explore its antifungal mechanism.

Results

The B. velezensis 20507 genome comprised one circular chromosome with a length of 4,043,341 bp, including 3,879 genes, 185 tandem repeats, 87 tRNAs, and 27 rRNAs. Comparative genomic analysis revealed that our sequenced strain had the closest genetic relationship with Bacillus velezensis (GenBank ID: NC 009725.2); however, there were significant differences in the positions of genes within the two genomes. It is predicted that B. velezensis 20507 encode 12 secondary metabolites, including difficidin, macrolactin H, fengycin, surfactin, bacillibactin, bacillothiazole A-N, butirosin a/b, and bacillaene. Results showed that B. velezensis 20507 produced various antagonistic effects on six plant pathogen strains: Exserohilum turcicum, Pyricularia oryzae, Fusarium graminearum, Sclerotinia sclerotiorum, Fusarium oxysporum, and Fusarium verticillioides. Acid precipitation followed by 80% methanol leaching is an effective method for isolating the antifungal component ME80 in B. velezensis 20507, which can damage the membranes of S. sclerotiorum hyphae and has good heat resistance. Using high-performance liquid chromatography, and Mass Spectrometry analysis, it is believed that fengycin C72H110N12O20 is the main active antifungal substance.

Discussion

This study provides new resources for the biological control of S. Sclerotiorum in soybeans and a theoretical basis for further clarification of the mechanism of action of B. velezensis 20507.