Chitinase-overproducing mutant of Serratia marcescens

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Abstract
Genetic modification of S. marcescens QMB1466 was undertaken to isolate mutants which produce increased levels of chitinolytic activity. After mutagenesis with UV light, ethyl methane sulfonate or N-methyl-N''-nitro-N-nitrosoguanidine, 19,940 colonies were screened for production of enlarged zones of clearing (indicative of chitinase activity) on chitin-containing agar plates; 44 chitinase high producers were tested further in shake flask cultures. Mutant IMR-1E1 was isolated which, depending on medium composition, produced 2-3 times more endochitinase [EC 3.2.1.14] activity than the wild type. IMR-1E1 produced 2-3 times more than the wild type of the other components of the chitinolytic enzyme system.sbd.a factor involved in the hydrolysis of crystalline chitin and chitobiase [EC 3.2.1.30]. After induction by chitin, endochitinase and chitobiase activity appeared at similar times for both IMR-1E1 and QMB1466, suggesting possible coordinate control of these enzymes. The results are consistent with IMR-1E1 containing a regulatory mutation which increased production of the components of the chitinolytic enzyme system and/or with IMR-1E1 containing a tandem duplication of the chitinase genes. The high rate of reversion of IMR-1E1 to decreased levels of chitinase production suggests that the overproduction of chitinase by IMR-1E1 is due to a tandem gene duplication.