Abstract
The over and repeated use of chemical bactericides to control plant bacterial diseases has resulted in unwanted effects, such as environmental pollution, residual toxicity, and resistance buildup in bacterial pathogens. Many previous studies have aimed to develop biological control agents to replace chemical bactericides. In this study, the antibacterial efficacy of the fermentation broth of Paenibacillus elgii JCK-5075 and its antibacterial compounds were evaluated against plant pathogenic bacteria, using both in vitro and in vivo bioassays. Pelgipeptins (PGPs) A, B, C, and D that were isolated from P. elgii JCK-5075 displayed broad-spectrum antibacterial activity against various plant pathogenic bacteria. The fermentation broth of P. elgii JCK-5075, at 5-fold dilution, effectively suppressed the development of tomato bacterial wilt, Kimchi cabbage soft rot, and red pepper bacterial leaf spot in pot experiments with control values of 81, 84, and 67%, respectively. PGP-A and C, at 200 μg/ml, were also found to markedly reduce the development of Kimchi cabbage bacterial soft rot by 75% and tomato bacterial wilt by 83%, respectively, and their disease control efficacy was comparable to that of oxolinic acid with control values of 81 and 85%, respectively. Additionally, the antibacterial activity of PGP-C was found to be directly correlated with membrane damage mechanisms. These results indicates that P. elgii JCK-5075 producing PGPs could be used as a biocontrol agent for the control of plant bacterial diseases. This is the first report on the in vitro and in vivo antibacterial activity of PGPs against bacterial plant pathogens.
Highlights
Even though fungal diseases are more numerous and severe in plants, there are several important pathogenic bacteria that can cause significant annual losses on a global scale, in moist and hot climatic conditions (Egli and Sturm, 1981)
During the discovery of the antimicrobial metabolites, we found that the PGP-A, B, C, and D, that were isolated from the P. elgii JCK-5075, were highly active at inhibiting the cell growth of various phytopathogenic bacteria
Fermentation filtrate of the P. elgii JCK-5075 exhibited a range of strong antibacterial effects against the 14 plant pathogenic bacteria, with Minimum inhibitory concentration (MIC) values of 0.63–10% (Table 1)
Summary
Even though fungal diseases are more numerous and severe in plants, there are several important pathogenic bacteria that can cause significant annual losses on a global scale, in moist and hot climatic conditions (Egli and Sturm, 1981). In order to replace chemical pesticides, biological control agents, including bioactive metabolites produced by microorganisms or the microbial cells themselves, have previously been intensively studied (Roth et al, 1997; Kim et al, 2009; Lugtenberg and Kamilova, 2009; Sundin et al, 2016; Tsuda et al, 2016). The interest in biological control agents has increased, owing to their benefits, which include that they may potentially be self-sustaining as they may spread on their own after initial establishment; that they may require a reduced input of non-renewable resources; and that they may result in long-term disease suppression in the environment. The biological agents that have been used previously were mostly based on bacteria (90%) and fungi (10%) (Yuliar et al, 2015)
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