Abstract
Biosurfactants are unique secondary metabolites, synthesised non-ribosomally by certain bacteria, fungi and yeast, with their most promising applications as antimicrobial agents and surfactants in the medical and food industries. Naturally produced glycolipids and lipopeptides are found as a mixture of congeners, which increases their antimicrobial potency. Sensitive analysis techniques, such as liquid chromatography coupled to mass spectrometry, enable the fingerprinting of different biosurfactant congeners within a naturally produced crude extract. Bacillus amyloliquefaciens ST34 and Pseudomonas aeruginosa ST5, isolated from wastewater, were screened for biosurfactant production. Biosurfactant compounds were solvent extracted and characterised using ultra-performance liquid chromatography (UPLC) coupled to electrospray ionisation mass spectrometry (ESI–MS). Results indicated that B. amyloliquefaciens ST34 produced C13–16 surfactin analogues and their identity were confirmed by high resolution ESI–MS and UPLC–MS. In the crude extract obtained from P. aeruginosa ST5, high resolution ESI–MS linked to UPLC–MS confirmed the presence of di- and monorhamnolipid congeners, specifically Rha–Rha–C10–C10 and Rha–C10–C10, Rha–Rha–C8–C10/Rha–Rha–C10–C8 and Rha–C8–C10/Rha–C10–C8, as well as Rha–Rha–C12–C10/Rha–Rha–C10–C12 and Rha–C12–C10/Rha–C10–C12. The crude surfactin and rhamnolipid extracts also retained pronounced antimicrobial activity against a broad spectrum of opportunistic and pathogenic microorganisms, including antibiotic resistant Staphylococcus aureus and Escherichia coli strains and the pathogenic yeast Candida albicans. In addition, the rapid solvent extraction combined with UPLC–MS of the crude samples is a simple and powerful technique to provide fast, sensitive and highly specific data on the characterisation of biosurfactant compounds.
Highlights
Biosurfactants are secondary metabolites that are nonribosomally synthesised by actively growing and/or resting microbial cells (Van Delden and Iglewski 1998; Ron and Rosenberg 2001; Mulligan 2005)
The current study focused on the purification and characterisation of antimicrobial glycolipid and lipopeptide biosurfactant compounds respectively, produced by Pseudomonas aeruginosa (P. aeruginosa) ST5 and Bacillus amyloliquefaciens (B. amyloliquefaciens) ST34 strains that were isolated from a local wastewater treatment plant
The current study focused on the partial purification and characterisation of the antimicrobial lipopeptide and glycolipid biosurfactant compounds produced by ST34 and ST5, respectively
Summary
Biosurfactants are secondary metabolites that are nonribosomally synthesised by actively growing and/or resting microbial cells (bacteria, fungi and yeast) (Van Delden and Iglewski 1998; Ron and Rosenberg 2001; Mulligan 2005). Rhamnolipids consist of one or two rhamnose residues in their hydrophilic moiety linked to one, two or three hydroxyl fatty acid chains of varying lengths (eight to 22 carbons) (Déziel et al 1999; Gunther et al 2005). Surfactin is a cyclic heptapeptide consisting of hydrophobic and negatively charged amino acids with a chiral sequence LLDLLDL linked to hydroxyl fatty acyl residue of between 12 and 16 carbon atoms (Seydlová and Svobodová 2008)
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