Improved production of rhamnolipids by a Pseudomonas aeruginosa mutant

A Pseudomonas aeruginosa mutant derived by random mutagenesis with N-methyl-N -nitro-N-nitrosoguanidine, producing high levels of the rhamnolipid biosurfactants was selected on Siegmund-Wagner [SW] plates. The mutant designated P. aeruginosa PTCC1637 produces rhamnolipids at concentrations 10 time more than parent strain. NMR analysis and surface tension measurement showed that the biosurfactants produced by the mutant were identical to those produced by the wildtype strain. The biosurfactants exhibited a low surface tension of 28.0 mN m-1 and a low critical micelle concentration of 9 mg l-1. Similar to the wildtype strain, the mutant produced biosurfactants at the stationary phase

Mutagenesis of leuconostoc mesenteroides and selection of dextransucrase hyperproducing strains.

Dextransucrase of Leuconostoc mesenteroides PTCC 1059 is an enzyme of industrial and medical interest that catalyzes the synthesis of a soluble dextran from sucrose. The mutant strains of Leuconostoc mesenteroides PTCC 1059 hyperproducing for dextransucrase were isolated after UV irradiation and treatment with ethyl methane sulfonate. The enzyme activity of one mutant strain, the 1059M5E4, was about 2.5-fold higher than that of the wild type, while its cell growth was relatively lower. The 1059M5E4 dextransucrase produced the same type of dextran as well as the wild type but showed higher thermal stability. These properties may be interesting for using this strain in enzymatic production of dextran