Abstract
The chemical and physical properties of extracellular rhamnolipid synthesized by a nonfluorescent Pseudomonas species soil isolate, identified as DYNA270, is described, along with characteristics of rhamnolipid production under varying growth conditions and substrates. The biosurfactant is determined to be an anionic, extracellular glycolipid consisting of two major components, the rhamnopyranoside β-1-3-hydroxydecanoyl-3-hydroxydecanoic acid (GU-6) and rhamnopyranosyl β→β2-rhamnopyranoside-β1-3-hydroxydecanoyl-3-hydroxydecanoic acid (GL-2), of molecular weight 504 and 649 daltons, respectively. These glycolipids are produced in a stoichiometric ratio of 1:3, respectively. The purified rhamnolipid mixture exhibits a critical micelle concentration of 20 mg/L, minimum surface (air/water interface) tension of 22 mN/m, and minimum interfacial tension values of 0.005 mN/m (against hexane). The pH optimum, critical micelle concentration, and effective alkane carbon number were established for Pseudomonas species DYNA270 and compared to those of rhamnolipid produced by Pseudomonas aeruginosa PG201. Significant differences are documented in the physical properties of extracellular rhamnolipids derived from these two microorganisms. The surface properties of this rhamnolipid are unique in that ultra-low surface and interfacial tension values are present in both purified rhamnolipid and culture broth containing the rhamnolipid complex (GU6 and GL2). We are not aware of prior studies reporting surface activity values this low for rhamnolipids. An exception is noted for an extracellular trehalose glycolipid produced by Rhodococcus species H13-A, which measured 0.00005 mN/m in the presence of the co-agent pentanol (Singer et al. 1990). Similar CMC values of 20 mg/L have been reported for rhamnolipids, a few being recorded as 5–10 mg/L for Pseudomonas species DSM2874 (Lang et al. 1984).
Highlights
Biosurfactants are surface active products derived from biological sources, which, like synthetic surfactants, possess the ability to dramatically lower interfacial tensions
An exception is noted for an extracellular trehalose glycolipid produced by Rhodococcus species H13-A, which measured 0.00005 mN/m in the presence of the co-agent pentanol (Singer et al 1990)
As rhamnolipids are typically harvested from culture media where the biosurfactant-producing microorganisms may be grown in a process run under a variety of nutrient, pH, and substrate conditions, the rhamnolipid production from this soil isolate and the associated culture broth properties were closely examined during growth on a number of different carbon sources under varying pH and nutrient conditions
Summary
Biosurfactants are surface active products derived from biological sources, which, like synthetic surfactants, possess the ability to dramatically lower interfacial tensions. Other biological structures with surface activity include phospholipids, sugar lipids, and certain antibiotics [7,9,10], Rhamnolipid biosurfactant structures and origins have been recently reviewed [11], and interest in their production and properties remains strong. This report describes the physical and chemical properties of an extracellular anionic glycolipid with unique surface properties synthesized by a newly isolated Pseudomonas species, DYNA270. As rhamnolipids are typically harvested from culture media where the biosurfactant-producing microorganisms may be grown in a process run under a variety of nutrient, pH, and substrate conditions, the rhamnolipid production from this soil isolate and the associated culture broth properties were closely examined during growth on a number of different carbon sources under varying pH and nutrient conditions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
