Genetic Modification of Strains

Slater and co-workers [38] reported that poly[3HB-co-3-hydroxyvalerate (3HV)] could be synthesised by a special mutant (atoC fadR) strain of Escherichia coli LS5218 harbouring the PHA biosynthesis genes of Cupriavidus necator, which enabled the constitutive expression of the enzymes responsible for the utilisation of short-chain fatty acids however, Escherichia coli LS5218 did not produce a high cell density culture. Next, Choi and Lee (1999) 

2007 Pseudomonas putida KT2442 Knockout mutation Poly(3HB-co- rncl-mk) [26] 

2014 Ralstonia eutropha Deletion mutations Poly(3HB-co- 3-mercapto- propionate) [33] 

2015 Escherichia coli In vitro recombination Poly(3HB-co- 3HHx) [34] 

In another study by Dennis and co-workers [41], the PHA accumulation of several microorganisms Escherichia coli, Klebsiella aerogenes and PHA-negative mutants of Cupriavidus necator and Pseudomonas putida) that expressed the phaC and acetoacetyl-coenzyme A reductase phaB) of Cupriavidus necator were analysed. This results in a construct that puts phaC and phaB under the control of the original Cupriavidus necator promoter. It was found that wild-type Cupriavidus necator was able to produce sc/-PHA, however the recombinant Cupriavidus necator expressing its own phaC and phaB without P-ketothiolase phaA) were able to accumulate poly(3HB-co-3HHx) when cultivated with even number chain fatty acids. The same trend was reported for Klebsiella aerogenes and Pseudomonas putida. 

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The efforts in reducing the production costs for biosurfactants have taken three basic routes the use of less expensive carbon sources, the genetic modification of strains to improve surfactant yield and the improvement in the method of separation of the surfactant from the cell culture [19], We will describe in more detail the efforts made in using waste biomass as the source of carbon and nutrients for the synthesis of biosurfactants. 

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