Determination of minimum inhibitory concentrations of sophorolipids against selected halotolerant and moderately halophilic bacteria, and extremely halophilic archaea isolated from salt samples and salted skins

Authors: Ashby, Richard - Rick; BIRBIR, MERAL - Marmara University; YILMAZ, PINAR - Marmara University; Msanne, Joseph; VENTOSA, ANTONIO - University Of Sevilla; YILMAZ, ELIF - Marmara University

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Microbial strains that are capable of breaking down proteins (proteolytic) and lipids (lipolytic) within animal hides cause substantial damage in hide processing. Many of these organisms can survive and even thrive in high salt conditions causing additional problems because historically, salt has been the primary means of curing hides in leather making. Proteolytic and lipolytic microbes can damage the hides by inducing the formation of irregularities on the surface of the hide which diminishes the quality of the product. Additionally, the use of high amounts of salt can cause environmental concerns depending on the salt runoff after use. This study was focused on the utilization of biodegradable molecules known as sophorolipids as antimicrobial agents that are effective against salt-associated microbes. Sophorolipids are documented to possess antimicrobial properties against many different bacterial strains and in this study they were tested against and effective in inhibiting the individual salt tolerant microbes isolated from salt washes or salted hides. The results of this study provide a potential alternative to using large amounts of salt in the hide curing process and will also reduce the concentration of salt tolerant hide degrading microbes that may be present throughout curing thus improving the overall procedure associated with the production of high quality leather.

Technical Abstract: Sophorolipids (SLs) are fungal/yeast glycolipids that possess antimicrobial activity. In this study, three different SL mixtures were produced by microbial fermentation from oleic acid (SL-o), palmitic acid (SL-p), and stearic acid (SL-s), and tested for their antimicrobial activity against various halotolerant and moderately halophilic bacteria, and against extremely halophilic archaea that were isolated from salt and salted skin samples, as well as bacterial and extremely halophilic archaeal reference strains. The minimum inhibitory concentrations (MICs) of each of the SLs against known halotolerant and halophilic microorganisms were determined by the broth microdilution test method using resazurin dye. The extremely halophilic archaeal strains were most susceptible to the antimicrobial action of the tested SLs with MIC values as low as 3.42 ug/mL. Conversely, the spore-forming halotolerant test strains, although susceptible to SLs, showed MIC values as high as 109.38 ug/mL. The SL-o, SL-p, and SL-s each exhibited broad-spectrum activity, demonstrating growth-inhibition against ten salt-associated bacterial strains and three archaeal strains possessing proteolytic activity, lipolytic activity, or both properties. In addition, each of the SLs showed growth-inhibition against three bacterial reference strains and two extremely halophilic archaeal reference strains. The findings from this study suggest that SL-o, SL-p, and SL-s could be utilized as eco-friendly antimicrobial agents, effectively contributing to the preservation of the leather industry’s salted skins and hides without the need for more environmentally deleterious processes.