Demonstration of bioprocess factors optimization for enhanced mono-rhamnolipid production by a marine Pseudomonas guguanensis

Abstract

We identified that Pseudomonas guguanensis produced macromolecular mono-rhamnolipid (1264.52 Da) upon sensing n-hexadecane/diesel/kerosene from its surroundings. Permutation experiments were done to improve the laboratory-scale mono-rhamnolipid production (ie, a three-fold increase) using RSM validation. Consequently, maximal mono-rhamnolipids production [40-50 mg/L] and emulsification abilities [65-70%] were encountered on day 8 using vegetable oil, peptone + yeast extract. EI₂₄ values for the rhamnolipids were found to be 78±1.75% at 12.5 mg/ mL. Production and secretion of rhamnolipids were accompanied by aggregation of cells at day 6 as pictured in SEM. Pure monorhamnolipids of P. guguanensis was found to lower the surface tension of water to 32.98±0.3 mN/m than the crude and CFSs of P. aeruginosa indicating efficient activity. Utilization and subsequent removal of hexadecane was 77.2% and the breakdown products were fatty acids [decanoic, hexadecanoic, octadecanoic acids and methyl stearates] as signified in Head-space GC-MS. The breakdown products of hexadecane are also present in the synthesized rhamnolipids suggesting their biosynthetic role. Rapid degradation of hexadecane, diesel and kerosene by this emulsifier combined with non-pathogenic trait of P. guguanensis identifies this organism as a viable option to remove n-alkanes from aquatic environments.

Keywords: GC–MS analysis; Hexadecanoic acids; High-molecular weight emulsifier; Mono-rhamnolipids; P. guguanensis; Pseudodroplets; RSM.