Previous studies have established that subinhibitory concentrations of antibiotics or antimicrobials are potent modulators of transcription process in bacterial cells. Hence, the bacteria might be introduced new proteins in mild stress environments like in the presence of antimicrobial agents at low concentrations. Although, there are still limited studies on the potential of antimicrobials at low doses play as a signaling agent that capable to modulate biological functions in bacteria. Therefore, this study aims to explore proteins production by Lactobacillus plantarum ATCC 8014 during stress which is in the presence of ethyl pentanoate at sub-minimal inhibitory concentration (sub-MIC). The Minimum Inhibition Concentration (MIC) of ethyl pentanoate against L. plantarum is 14.29% and was performed by microdilution assay. L. plantarum cells were treated with ethyl pentanoate at sub-MIC (0.05 x MIC) in the fermentation process. Two new protein bands (approximate size of 46.51 kD and 6.91 kD) were detected for the treated bacteria showed by SDS-PAGE profile. Of the two bands, eight possible proteins were identified by LC-MS/MS analysis. Thus, L. plantarum ATCC 8014 capable to produce new proteins in mild stress condition with the presence of 0.05 x MIC ethyl pentanoate. Futhermore, the isolated microbial proteins exhibit antimicrobial activity against several Gram-positive and Gram-negative bacteria. Copyright © WJSTR, all rights reserved.

Many studies have reported that the primary activity of most inhibitors of bacterial function is to modulate transcription processes at much lower concentrations than that required for antibiosis. Therefore, the bacteria might be produced and secreted more proteins in the mild stress surroundings (e.g. in the presence of low doses of antimicrobial agents) than in the normal environment. However, not much is known about unexpected ability of natural antimicrobial compounds at low concentration to become a signaling agent that capable to modulate biological functions in bacteria. Thus, this study aims to explore the potential of natural antimicrobial compound (Allium sativum) at sub-minimal inhibitory concentration (sub-MIC) in regulating proteins production by Bacillus subtilis ATCC 21332. The Minimum Inhibition Concentration (MIC) of A. sativum on B. subtilis resulting 14.29% was determined by microdilution assay. The bacteria cells were further exposed to A. sativum at sub-MIC (0.05 x MIC) in fermentation process. SDS-PAGE profile showed that two protein bands with approximate size of 51.36 kD and 9.74 kD were produced for the bacteria treated with A. sativum. LC-MS/MS analysis identified six possible proteins from the two bands expressed in mild stress condition. The proteins exhibited antimicrobial activity towards several Gram-positive and Gram-negative bacteria. Hence, B. subtilis ATCC 21332 in mild stress condition with the presence of 0.05 x MIC A. sativum could regulate bioactive proteins production. Copyright © AJBCPS, all rights reserved. Keywords: Bacillus subtilis ATCC 21332, Allium sativum, proteins, sub-MIC, antimicrobial agent, transcription