Chromomycin, an antibiotic produced by Streptomyces flaviscleroticus might play a role in the resistance to oxidative stress and is essential for viability in stationary phase.

The well-known role of antibiotics in killing sensitive organisms has been challenged by the effects they exert at subinhibitory concentrations. Unfortunately, there are very few published reports on the advantages these molecules may confer to their producers. This study describes the construction of a genetically verified deletion mutant of Streptomyces flaviscleroticus unable to synthesize chromomycin. This mutant was characterized by a rapid loss of viability in stationary phase that was correlated with high oxidative stress and altered antioxidant defences. Altered levels of key metabolites in the mutant signalled a redistribution of the glycolytic flux toward the PPP to generate NADPH to fight oxidative stress as well as reduction of ATP-phosphofructokinase and Krebs cycle enzymes activities. These changes were correlated with a shift in the preference for carbon utilization from glucose to amino acids. Remarkably, chromomycin at subinhibitory concentration increased longevity of the non-producer and restored most of the phenotypic features' characteristic of the wild type strain. Altogether these observations suggest that chromomycin may have antioxidant properties that would explain, at least in part, some of the phenotypes of the mutant. Our observations warrant reconsideration of the secondary metabolite definition and raise the possibility of crucial roles for their producers.

DNA binding characteristics of mithramycin and chromomycin analogues obtained by combinatorial biosynthesis.

The antitumor antibiotics mithramycin A and chromomycin A(3) bind reversibly to the minor groove of G/C-rich regions in DNA in the presence of dications such as Mg(2+), and their antiproliferative activity has been associated with their ability to block the binding of certain transcription factors to gene promoters. Despite their biological activity, their use as anticancer agents is limited by severe side effects. Therefore, in our pursuit of new structurally related molecules showing both lower toxicity and higher biological activity, we have examined the binding to DNA of six analogues that we have obtained by combinatorial biosynthetic procedures in the producing organisms. All these molecules bear a variety of changes in the side chain attached to C-3 of the chromophore. The spectroscopic characterization of their binding to DNA followed by the evaluation of binding parameters and associated thermodynamics revealed differences in their binding affinity. DNA binding was entropically driven, dominated by the hydrophobic transfer of every compound from solution into the minor groove of DNA. Among the analogues, mithramycin SDK and chromomycin SDK possessed the higher DNA binding affinities.

Aureolic acids: similar antibiotics with different biosynthetic gene clusters.

In this issue of Chemistry & Biology, Méndez and colleagues describe the sequence and organization of the chromomycin gene cluster. Unexpectedly, the arrangement is starkly different from the mithramycin biosynthetic cluster, despite similarity in the individual genes and the near identical structures of the two antibiotic aureolic acids.

Enzymatic conversion of glucose to UDP-4-keto-6-deoxyglucose in Streptomyces spp.

All of the 2,6-dideoxy sugars contained within the structure of chromomycin A3 are derived from D-glucose. Enzyme assays were used to confirm the presence of hexokinase, phosphoglucomutase, UDPG pyrophosphorylase (UDPGP), and UDPG oxidoreductase (UDPGO), all of which are involved in the pathway of glucose activation and conversion into 2,6-dideoxyhexoses during chromomycin biosynthesis. Levels of the four enzymes in Streptomyces spp. cell extracts were correlated with the production of chromomycins. The pathway of sugar activation in Streptomyces spp. involves glucose 6-phosphorylation by hexokinase, isomerization to G-1-P catalyzed by phosphoglucomutase, synthesis of UDPG catalyzed by UDPGP, and formation of UDP-4-keto-6-deoxyglucose by UDPGO.

Biogenesis of chromomycin A3 by Streptomyces griseus.

The biosynthesis of chromomycin A3 was investigated using 13C-labeled acetates, methionine and glucose, and 13C,18O-labeled acetate. 13C NMR spectral analysis demonstrated that: Aglycone assembly occurs by combining at least two polyketide chains; three of nine oxygen atoms of the aglycone originate from acetate precursor oxygen atoms; carbon methylations on the aromatic ring at C-7, on the chromose B sugar, and two O-methylations appear to be carried out by S-adenosyl-methionine requiring methyl transferases; and glucose is the precursor for all the sugars.

[Polymorphism of a culture of the chromomycin producer, Actinomyces aburaviensis var. verrucosus]. / Polimorfizm kul'tury produtsenta khromomitsina Actinomyces aburaviensis var. verrucosus

Polymorphism of the chromomycin-producing orgnaism Act. aburaviensis var. verrucosus 144--3 was studied. The stable variants differed in the morphologo-cultural properties, assimilation of the carbon sources, the component composition of the luminescence substances and the quantitative property of the antibiotic production. A substance with violet luminescence was found in the culture of varient I in addition to chromomycin. Similarity of the phenotypes observed in variants 1 and 2 when grown on complex organic media is explained by intensive chromomycin production by variant 1 on such media. Active colonies may be selected according to the colour due to chromomycin. Forms with an activity almost 4 times higher than that of the initial culture were found among the colonies of variant 2.