화학공학소재연구정보센터
Current Microbiology, Vol.29, No.6, 311-318, 1994
ISOLATION AND CHARACTERIZATION OF 5 GENOTYPIC MUTANTS OF CHLORATE-RESISTANT CYANOBACTERIA UNABLE TO UTILIZE NITRATE
Spontaneous mutants of the cyanobacterium Synechococcus PCC 7002 resistant to chlorate were isolated. Either 40 mM or 400 mM Na2ClO3 was used as the selective agent. Putative Chl(r) colonies were picked onto medium containing ammonia as the sole N source, then replica-plated to media containing either NH4+, NO2-, or NO3- as N sources. Of 252 putative mutants, 106 were able to use either NH4Cl or NaNO2 but not NaNO3 as their sole source of nitrogen. All of the mutant isolates had generation times similar to wild-type 7002 when grown on either ammonium (3.8-4.1 h/generation) or nitrite (4.5-4.7 h/generation). None had detectable methyl viologen-supported nitrate reductase activity and are thus phenotypically NRase(-). The Chl(r) mutants had photomediated O-2 production and dark O-2 uptake rates similar to the wild type and responded similarly to selected metabolic inhibitors. They expressed increased levels of phycocyanin (PC) synthesis under normal, nitrogen-replete growth conditions, but rapidly lapsed into a chlorotic state upon a shift to either medium containing nitrate or to N-free medium. Genetic analysis of the Chl(r) mutants indicated that each could be rescued by direct transformation with chromosomally derived DNA from the wild-type strain. Frequencies of transformation for the mutants were characteristic for single genetic lesions in this cyanobacterium. On the basis of marker rescue by a cosmid library of wild-type DNA, the NRase(-) mutants could be grouped into five distinctive genotypic families.