Abstract
Rhamnolipid production was monitored for a period of 216 h using different substrates in Pseudomonas aeruginosa PAO1 and Burkholderia thailandensis E264 which showed comparable crude yields attained by both after 216 h. The crude yield for P. aeruginosa, however, was significantly higher at the early stages of fermentation (72 or 144 h). Additionally, P. aeruginosa produced rhamnolipid with odd and even carbon chain lipid moieties using odd carbon chain fatty acid substrates (up to 45.97 and 67.57%, respectively). In contrast, B. thailandensis produced rhamnolipid with predominantly even carbon chain lipid moieties (up to 99.26). These results indicate the use of the fatty acid synthesis (FAS II) pathway as the main source of lipid precursors in rhamnolipid biosynthesis by B. thailandensis. Isotope tracing using 0.25% stearic acid – d35 + 1% glycerol as carbon substrate showed a single pattern of deuterium incorporation: with predominantly less than 15 deuterium atoms incorporated into a single Di-C14-C14 rhamnolipid molecule. This further indicates that the FAS II pathway is the main source of the lipid precursor in rhamnolipid biosynthesis by B. thailandensis. The pathogenicity of these strains was also assessed, and results showed that B. thailandensis is significantly less pathogenic than P. aeruginosa with an LC50 at 24 h > 2500, approximately three logs higher than P. aeruginosa using the Galleria mellonella larva model.
Highlights
The first report of rhamnolipid production was made in the mid twentieth century, with Pseudomonas aeruginosa identified as the producer organism
Microbial growth and rhamnolipid production by B. thailandensis and P. aeruginosa. Both B. thailandensis and P. aeruginosa were grown for a period of 216 h at 30 °C in mineral salt media (MSM) or peptone/glucose acid salt media (PPGAS) media supplemented with different carbon sources
B. thailandensis reached an early stationary phase at 24 h and a late stationary phase at 72 h in media supplemented with fatty acids, or 120 h in media supplemented with glycerol
Summary
The first report of rhamnolipid production was made in the mid twentieth century, with Pseudomonas aeruginosa identified as the producer organism. Production of rhamnolipid from strains of P. aeruginosa has been extensively investigated to understand the structure, cellular function and mechanism of rhamnolipid production by this organism (Irorere et al 2017). Heightened industrial interest has led to an increased demand for rhamnolipids and concerns about the safety of the product and its industrial production processes, since P. aeruginosa is an opportunistic human pathogen. These facts have stimulated the search for alternative, safer rhamnolipid producing microorganisms. The orthologues of the rhamnolipid genes (rhlA, rhlB and rhlC) have been
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