Purification, characterization, and heterologous expression of an antifungal protein from the endophytic Bacillus subtilis strain Em7 and its activity against Sclerotinia sclerotiorum

The antimicrobial activity of protein elicitor AMEP412 against Streptomyces scabiei

In this paper, we report the antimicrobial activity of AMEP412 (a protein elicitor from Bacillus subtilis) against Streptomyces scabiei, which is the potato common scab pathogen. The purified protein samples showed an obvious inhibition zone on an S. scabiei agar plate, and the minimum inhibition concentration detected was 50 μg mL^-1. The fluorescence localization assay revealed that AMEP412 could bind to aerial mycelia and spores. The stability test showed that AMEP412 was stable at 60 °C for 30 min and in pH values from 5.0 to 10.0. Its antimicrobial activity was not sensitive to metal cations. However, its activity declined by 23% when treated with Proteinase K, and was completely abrogated with Tween 80 treatment. Three antimicrobial peptides (GS21, GY20 and GY23) were identified from AMEP412, which further verified its antimicrobial activity. This research reveals the antimicrobial function of AMEP412, which not only enriches the function of the protein elicitor, but also provides a candidate for the biocontrol of potato common scab.

Genomics-guided discovery and structure identification of cyclic lipopeptides from the Bacillus siamensis JFL15

In this research, a strain with broad-spectrum antimicrobial activities was isolated from the gastrointestinal tract of hairtail (Trichiurus haumela) and identified as Bacillus siamensis JFL15 through morphological, 16S rRNA, and average nucleotide identity analyses. The genome of B. siamensis JFL15 was sequenced, and three gene clusters involved in the biosynthesis of surfactin (srf), bacillibactin (dhb), and fengycin (fen) were predicted through antiSMASH analysis. The combined genomics-metabolics profiling of the strain revealed 20 active compounds, which belong to four main types of cyclic lipopeptides produced by Bacillus species: bacillibactin, iturin, fengycin, and surfactin. Among these lipopeptides, two high-purity antifungal components, namely, components b and c, were successfully identified as iturin A and bacillomycin F. The minimum inhibitory concentrations (MICs) of iturin A for Magnapothe grisea, Rhizoctorzia solani, and Colletotrichum gloeosporioides were 125.00, 62.50, and 125.00 μg/ml, respectively, whereas the MICs of bacillomycin F for these three organisms were 62.50, 31.25, and 62.50 μg/ml, respectively. The mechanism of bacillomycin F and iturin A against M. grisea was also investigated. Scanning electron microscopy (SEM) indicated that the surface of the hypha treated with iturin A or bacillomycin F became sunk, lumpy, and wrinkled. The diversity of the identified and predicted compounds from B. siamensis JFL15 suggested that this strain might be a promising biocontrol agent for an effective and environmentally friendly control of pathogenic microorganisms. To the best of our knowledge, this study is the first to describe cyclic lipopeptides purified and identified from B. siamensis.