Bacillus genus produces several secondary metabolites with biocontrol ability against various phytopathogens. Bacillus velezensis AK-0 (AK-0), an antagonistic strain isolated from Korean ginseng rhizospheric soil, was found to exhibit antagonistic activity against several phytopathogens. To further display the genetic mechanism of the biocontrol traits of AK-0, we report the complete genome sequence of AK-0 and compared it with complete genome sequences of closely related strains. We report the biocontrol activity of AK-0 against apple bitter rot caused by Colletotrichum gloeosporioides, which could lead to commercialization of this strain as a microbial biopesticide in Korea. To retain its biocontrol efficacy for a longer period, AK-0 has been formulated with ingredients for commercialization, named AK-0 product formulation (AK-0PF). AK-0PF played a role in the suppression of the mycelial growth of the fungicide-resistant pathogen C. gloeosporioides YCHH4 at a greater level than the non-treated control. Moreover, AK-0PF exhibited greater disease suppression of bitter rot in matured under field conditions. Here, we report the complete genome sequence of the AK-0 strain, which has a 3,969,429 bp circular chromosome with 3808 genes and a G+C content of 46.5%. The genome sequence of AK-0 provides a greater understanding of the Bacillus species, which displays biocontrol activity via secondary metabolites. The genome has eight potential secondary metabolite biosynthetic clusters, among which, ituD and bacD genes were expressed at a greater level than other genes. This work provides a better understanding of the strain AK-0, as an effective biocontrol agent (BCA) against phytopathogens, including bitter rot in apple.

The present study describes the bacterial blight of walnut, caused by Xanthomonas arboricola pv. juglandis ( Xaj ) in the northern Gyeongbuk province, Korea. Disease symptoms that appear very similar to anthracnose symptoms were observed in walnut trees in June 2016. Pathogens were isolated from disease infected leaves, fruits, shoots, bud, flower bud of walnut, and cultured onto yeast dextrose carbonate agar plates. Isolated bacteria with bacterial blight symptoms were characterized for their nutrient utilization profiles using Biolog GN2 and Vitek 2. In addition, isolates were subjected to physiological, biochemical, and morphological characterizations. Furthermore, isolates were identified using 16S rDNA sequence analysis, and multi-locus sequence analysis using atpD , dnaK , efp , and rpoD . To confirm pathogenicity, leaves, fruits, and stems of 3-year-old walnut plants were inoculated with bacterial pathogen suspensions as a foliar spray. One week after inoculation, the gray spots on leaves and yellow halos around the spots were developed. Fruits and stems showed browning symptoms. The pathogen Xaj was re-isolated from all symptomatic tissues to fulfill Koch’s postulates, while symptoms were not appeared on control plants. On the other hand, the symptoms were very similar to the symptoms of anthracnose caused by Colletotrichum gloeosporioides . When walnut plants were inoculated with combined pathogens of Xaj and C. gloeosporioides , disease symptoms were greater in comparison with when inoculated alone. Xaj population size was more in the month of April than March due to their dormancy in March, and sensitive to antibiotics such as oxytetracycline and streptomycin, while resistant to copper sulfate.

Anthracnose is a fungal disease caused by Colletotrichum species and has detrimental effects on many crops, including red pepper. This study used Bacillus tequilensis GYUN-300 (GYUN-300), which exhibit antagonistic activity against the fungal pathogen, Colletotrichum acutatum. This pathogen causes anthracnose that manifests primarily as a fruit rot in red pepper. There have been little efforts to identify antagonistic bacteria from mushrooms; this strain of bacteria was identified as B. tequilensis using BIOLOG and 16S rDNA sequencing analysis. The genetic mechanism underpinning the biocontrol traits of GYUN-300 was characterized using the complete genome sequence of GYUN-300, which was closely compared to related strains. GYUN-300 inhibited mycelial growth and spore germination of C. acutatum under in vitro conditions. Important antagonistic traits, such as siderophore production, solubilization of insoluble phosphate, and production of lytic enzymes (cellulase, protease, and amylase), were observed in GYUN-300, These trains promoted growth in terms of seed germination and vigorous seedling growth compared to the non-treated control. When red pepper fruits were treated with GYUN-300, the preventive and curative effects were 66.6 and 38.3% effective, respectively, in wounded red pepper fruits; there was no difference between the preventive and curative effects in non-wounded red pepper fruits. Furthermore, GYUN-300 was resistant to several commercial fungicides, indicating that GYUN-300 bacterial cells may also be used synergistically with chemical fungicides to increase biocontrol efficiency. Based on in vitro results, GYUN-300 played a role to control anthracnose disease effectively in field conditions when compared to other treatments and non-treated controls. The results from this study provide a better understanding of the GYUN-300 strain as an effective biocontrol agent against red pepper anthracnose; this form of biocontrol provides an environment-friendly alternative to chemical fungicides.

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