Triple knockout of frdC gltA and pta genes enhanced pHA production in Escherichia coli

Polyhydroxyalkanoate (PHA) is a linear polyester produced through the fermentation of sugar or lipid. Biosynthesis of PHA comprises three enzymes known as acetyl-CoA acetyltransferase (phaA), acetoacetyl-CoA reductase (phaB) and PHA synthase (phaC). Comamonas sp. is one of the strains commonly used for PHA production. In order to develop higher PHA production from bacterial respond strategy, PHA biosynthesis operon of Comamonas sp. EB172 was introduced into Escherichia coli BW25113 through a pGEM-T vector. E. coli was chosen due to the complete genome information available and the absence of depolymerisation gene, phaZ. In this study, the deletion of several single genes, which are frdC, gltA, and pta, was found to be associated with PHA metabolism activity in E. coli BW25113. P1 transduction was performed to construct multiple genes knockout. The engineered strain, E. coli BW25113 frdCgltApta::kan/pGEM’-phaCABCo, yielded the highest PHA production at 64 wt.% with 1.4 fold higher than that of control strain of E. coli BW25113/pGEM’-phaCABCo. This strain is potential for industrial application for higher PHA production from E. coli.

Further Studies with Lipoamide Dehydrogenase Mutants of Escherichia coli k12

The immunological properties of ten lipoamide dehydrogenase mutants of Escherichia coli were investigated with antiserum raised against purified lipoamide dehydrogenase. Seven mutants were CRM+ (cross-reacting material present) as they contained lipoamide dehydrogenase proteins exhibiting either complete or partial immunological identity with the wild-type protein. This indicates that at least seven of the mutations affect the lipoamide dehydrogenase structural gene (lpd). The remaining three mutants (CRM-) contained no detectable cross-reacting protein. None of the lpd mutations were sensitive to any of three different amber-suppressors. Genetic analysis by P1-transduction showed that all the lpd mutant sites were clustered very near the distal gene (aceF) of the ace region which specifies the dehydrogenase (aceE) and transacetylase (aceF) components of the pyruvate dehydrogenase multienzyme complex. Calculations based on the recombination frequency between an aceF mutant and the nearest lpd mutant site support the conclusion that apart from the possible presence of a regulatory element, the aceF and lpd genes are contiguous.

Genetic studies of H group plasmids by bacteriophage P1 transduction

Bacteriophage P1 transduction was used to study the incompatibility group H1 plasmid pRG1251, molecular weight 120 × 106, and the incompatibility group H2 plasmid pSD114, molecular weight 166 × 106. The order of resistance (R) determinants on pSD114 was deduced from transduction and segregation experiments to be chloramphenicol-tetracycline-kanamycin-streptomycin. Resistance to tellurium and to coliphages, which are properties also encoded by many H2 plasmids, were not transduced with the other markers. On pRG1251, the ampicillin and tetracycline resistance markers appear to be located together, as do the chloramphenicol, streptomycin, and sulfamethoxazole resistance markers. Frequently, blocks of R determinants were transposed to the P1 genome or to the Escherichia coli chromosome. P1 DNA was isolated which carried the chloramphenicol, streptomycin, and sulfamethoxazole markers from pRG1251 and had a molecular weight of 64 × 106. Other P1 prophages carried R determinants from pSD114 and had molecular weights of 86 × 106. A plasmid of molecular weight 124 × 106 was also isolated which contained incompatibility determinants from P1 (incompatibility group Y) and from the H2 group plasmid. The mechanism of formation of these unusual plasmid species is discussed.