Characterization of Supernatant Extract and Viability of Bacillus Subtilis Km16 and Pseudomonas Spp. In Fish Feed as Biocontrol Agents Against Aquaculture Pathogens

Abstract

The use of biocontrol agent in aquaculture is being adapted as an effective alternative to antibiotics which can lead to the elaboration of antibiotic-resistant bacteria and confer unpleasant impacts to aquatic organisms. Aquatic bacteria have been discovered as biocontrol agents and potential probiotic candidates to improve the health of aquatic organisms, feed efficiency, and disease resistance to aquaculture pathogens. However, local isolate has not intensively been explored and used to increase aquaculture sector productivity. Therefore, this research aimed to determine minimum inhibitory concentrations of their antibacterial compounds against aquaculture pathogens and to characterize aquatic bacteria by their viability in the feed. Four isolates from several aquatic environments in Indonesia (Pseudomonas sp. S1.1, Pseudomonas sp. S1.2, Pseudomonas sp. SL1.1, and Bacillus subtilis KM16) were used to characterize of antibacterial compound and to determine the viability in feed. Ethyl acetate extracts from all isolates showed better antibacaterial activity against Aeromonas hydrophila and Vibrio vulnificus than chloroform and dichloromethane extracts, in which ethyl acetate extract from Bacillus subtilis KM16 showed the strongest antibacterial activity. Pseudomonas spp. were more effective against V. vulnificus (40 mg/mL) and Bacillus subtilis KM16 was more effective against A. hydrophila (20 mg/mL), as proved by the minimum inhibitory concentrations of their ethyl acetate extracts. In this research, Bacillus subtilis KM16 had stable viability in feed than Pseudomonas sp. isolates.

Phyllosphere bacteria with antiquorum sensing and antibiofilm activities against fish pathogenic bacteria

“…Each phyllosphere isolates may have different bioactive compounds that have different antibiofilm mechanisms against pathogenic bacteria. AHL-lactonase is an enzyme produced by phyllosphere bacteria that could cleave the lactone ring in AHL where AHL is used by Gram-negative bacteria such as A. hydrophila and V. harveyi [ 7 , 21 ]. Each pathogen also has a different EPS component which can be degraded by different bioactive components, for example, enzymes such as proteases, glycoside hydrolases, and deoxyribonucleases.…”

“…Meanwhile, the pectinase enzyme works as an antibiofilm agent by degrading the structure of EPS [ 29 ]. Bacillus subtilis has also been found to produce antibiofilm agents such as proteins and exopolysaccharides [ 21 ]. Surfactin, fengycin, and iturin are lipopeptides produced by Bacillus subtilis and act as anti-adhesive agents in inhibiting biofilm formation by changing the hydrophobicity of the cell surface.…”