Biosynthesis of Novel Sophorolipids

A comparison of the surface-active properties of those two compounds revealed only a minor difference the lauryl sophoroside lowered the surface tension of water from 72 to 33mN/m whereas the commercially available alkyl polyglycoside (APG) 1200 Plantaren , which on average has 1.3 glucose units per molecule, performed somewhat better and lowered the surface tension to 27 mN/m. 

It is interesting to note that this method not only increases the range of obtainable sophorolipids but also provides a biological way to perform the stereospecific hydroxylation of a number of substrates. All that is required of such a substrate is that it contains a function that allows an elongator molecule to be attached and removed and that the target site for hydroxylation is sterically accessible. 

Rhamnolipid 1 and rhamnolipid 3 are the major rhamnolipids produced by using resting cells of Pseudomonas aeruginosa DSM 2874. Two further rhamnolipids that are similar in structure but contain only one hydroxydecanoic acid unit, rhamnolipids 2 and 4, have also been detected. The rhamnolipid production with resting cells is a two-step process. In a first step Pseudomonas aeruginosa cells are produced and harvested. In a second step this biomass is used for the rhamnolipid production under growth-limiting conditions [29], 

Another aspect prone to improvement is the product separation and purification step. This is particularly challenging due to high protein and alginate concentrations that tend to clog membrane filters, resulting in a drastically reduced transmembrane flux. In addition to this, rhamnolipids aggregate in micelles of about the same size as Pseudomonas cells, which obviously complicates solvent-free product separation. 

Of the cell-free supernatants of strains grown on frying oils, those of P. aeruginosa 47T2 and of eight other Pseudomonas strains showed surface tension values from 32 to 36mN/m [32]. An emulsion with kerosene remained stable for three months. Abalos and co-workers [33] cultured P. aeruginosa ATIO in a mineral salts medium with 5% of waste-free fatty acids in a food-oil refinery. The final production of rhamnolipids was 9.5 g/1 after 96 hours. The surface tension of the supernatant reached 28 mN/m at this time. 

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