Pepper bacterial wilt is caused by the bacterial pathogen, Ralstonia solanacearum. It is the most destructive disease of many Solanaceous crops such as potatoes, tobacco, pepper, tomatoes and eggplant and is a significant source of crop loss worldwide. Physical, cultural and chemical controls have been employed to combat this destructive disease. However, none of these strategies has been able to control the disease completely due to the broad host range and genetic diversity of the pathogen, its prolonged survival in the soil and survival on vegetation as a latent infection. Owing to co-management strategies, biological control is the best approach for human health and environmental friendly motivations. It makes use of various antagonistic rhizobacteria and epiphytic species such as Bacillus cereus, Pseudomonas putida, Bacillus subtilis, Paenibacillus macerans, Serratia marcescens, Bacillus pumilus and Pseudomonas fluorescens, which compete with and ultimately inhibit the growth of the pathogen. The possible mechanisms of biocontrol by these species involve multifaceted interactions between the host, pathogen and the antagonists. These can involve competition for nutrients and space, plant-mediated systemic resistance, siderophore production and production of extracellular cell wall degrading enzymes to inhibit or suppress the growth of the bacterial wilt agent.
Fresh produce vegetables are colonized by different bacterial species, some of which are antagonistic to microbes that cause postharvest losses. However, no comprehensive assessment of the diversity and composition of bacteria inhabiting surfaces of fresh pepper plants grown under different conditions has been conducted. In this study, 16S RNA amplicon sequencing was used to reveal bacterial communities inhabiting the surfaces of red and green pepper (fungicides-treated and non-fungicides-treated) grown under hydroponic and open field conditions. Results revealed that pepper fruit surfaces were dominated by bacterial phylum Proteobacteria, Firmicutes, Actinobacteria, and, Bacteroidetes. the majority of the bacterial operation taxonomic units (97% similarity cutoff) were shared between the two habitats, two treatments, and the two pepper types. Phenotypic predictions (at phylum level) detected a high abundance of potentially pathogenic, biofilm-forming, and stress-tolerant bacteria on samples grown on open soils than those from hydroponic systems. Furthermore, bacterial species of genera mostly classified as fungal antagonists including; Acinetobacter, Agrobacterium, and Burkholderia were the most abundant on the surfaces. these results suggest that peppers accommodate substantially different bacterial communities with antagonistic activities on their surfaces, independent of employed agronomic strategies and that the beneficial bacterial strains maybe more important for peppers established on open fields, which seems to be more vulnerable to abiotic and biotic stresses.
Biological control of plant pathogens, particularly using microbial antagonists, is posited as the most effective, environmentally-safe, and sustainable strategy to manage plant diseases. However, the roles of antagonists in controlling bacterial wilt, a disease caused by the most devastating and widely distributed pathogen of sweet peppers (i.e., R. solanacearum), are poorly understood. Here, amplicon sequencing and several microbial function assays were used to depict the identities and the potential antagonistic functions of bacteria isolated from 80 red and green sweet pepper fruit samples, grown under hydroponic and open soil conditions, with some plants, fungicide-treated while others were untreated. Amplicon sequencing revealed the following bacterial strains: Bacillus cereus strain HRT7.7, Enterobacter hormaechei strain SRU4.4, Paenibacillus polymyxa strain SRT9.1, and Serratia marcescens strain SGT5.3, as potential antagonists of R. solanacearum. Optimization studies with different carbon and nitrogen sources revealed that maximum inhibition of the pathogen was produced at 3% (w/v) starch and 2,5% (w/v) tryptone at pH 7 and 30 °C. The mode of action exhibited by the antagonistic isolates includes the production of lytic enzymes (i.e., cellulase and protease enzymes) and siderophores, as well as solubilization of phosphate. Overall, the results demonstrated that the maximum antimicrobial activity of bacterial antagonists could only be achieved under specific environmental conditions (e.g., available carbon and nitrogen sources, pH, and temperature levels), and that bacterial antagonists can also indirectly promote crop growth and development through nutrient cycling and siderophore production.
Paenibacillus polymyxa
SRT9.1 is an epiphytic bacterium capable of inhibiting plant-pathogenic bacteria. The strain has potential for development as a biocontrol agent for use in agriculture. We report the whole-genome sequence of
Paenibacillus polymyxa
SRT9.1, consisting of 6,754,470 bp and 7,878 coding sequences, with an average G+C content of 45%.
Pediococcus acidilactici
is a beneficial lactic acid bacterium frequently studied for its probiotic potential. Here, we present a 2.32-Mb draft genome sequence of strain ISO17, with a G+C content of 42%. The genome was predicted to harbor 4 rRNA genes, 47 tRNA genes, and 2,297 protein-coding sequences.
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