Carbazole Antibiotics Synthesis in a Streptomyces tendae Bald Mutant, Created by Acriflavine Treatment

Acriflavine treatment on Streptomyces tendae generated a bald mutant (bid-1) with an altered antibiotic pattern. The parental strain produced nikkomycins and juglomycins, whereas the mutant bid-1 was only capable of juglomycin synthesis. The existence of a mutant defective in morphogenesis and in nikkomycin biosynthesis suggests a common regulation of these processes. An interesting finding of this study is that mutant bld-1 produced two carbazole derivatives, hitherto never seen in cultures of the parental strain. It seems likely that the DNA intercalating dye acriflavine, by mutagenesis, had activated cryptic genes which are involved in carbazole synthesis. The two carbazole derivatives were identified as the neuronal cell protecting compounds CS-79B and carquinostatin A, recently isolated from a wild-type of S. exfoliatus. We found that both substances showed antibacterial activity.

Cryptic Genes for Cellobiose Utilization in Natural Isolates of Escherichia coli

ABSTRACT The ECOR collection of natural Escherichia coli isolates was screened to determine the proportion of strains that carried functional, cryptic and nonfunctional genes for utilization of the three β-glucoside sugars, arbutin, salicin and cellobiose. None of the 71 natural isolates utilized any of the β-glucosides. Each strain was subjected to selection for utilization of each of the sugars. Only five of the isolates were incapable of yielding spontaneous β-glucoside-utilizing mutants. Forty-five strains yielded cellobiose+ mutants, 62 yielded arbutin+ mutants, and 58 strains yielded salicin+ mutants. A subset of the mutants was screen by mRNA hybridization to determine whether they were expressing either the cel or the bgl β-glucoside utilization operons of E. coli K12. Two cellobiose+ and two arbutin+-salicin+ strains failed to express either of these known operons. It is concluded that there are at least four gene clusters specifying β-glucoside utilization functions in E. coli populations, and that all of these are normally cryptic. It is estimated that in any random isolate the probability of any particular cluster having been irreversibly inactivated by the accumulation of random mutations is about 0.5.