An effective method was established for preparing the potent cell cycle inhibitor dehydrophenylahistin by a combination of chemical racemization of partially purified (±)-phenylahistin and enzymatic conversion of (−)-phenylahistin by the cell-free extract of Streptomyces albulus KO-23, an albonoursin-producing actinomycete. This method enables conversion of (+)-phenylahistin, which is present in the culture of Aspergillus ustus NSC-F038 and is not transformed by the Streptomyces enzyme, to dehydrophenylahistin.
This study investigated the biological characteristics of 43 actinomycete isolates from saline and alkaline soils in Xinjiang, Hebei and Qinghai and representative strains of four genera under differing conditions of pH and varying concentrations of the mineral salts Na+, K+, Mg2+ and Ca2+. The results indicated that halotolerant actinomycetes have extensive adaptability to Na+, K+ and Mg2+, but that few strains can grow even in low concentrations of CaCl2. Halophilic actinomycetes have extensive adaptability to Na+; for most, Na+ may be replaced by K+ or Mg2+, but not by Ca2+. Certain halophilic actinomycetes require Na+ to grow. It was also clear that the growth of all halophilic actinomycetes is dependent on different concentrations of Na+, K+ or Mg2+. We believe that only kaliumophilic or magnesiumophilic or calciumphilic actinomycetes may be found in high salt environments. In addition, the range of pH values in which growth occurred was 6.0∼10.0; optimum pH values were 7.0∼8.0 for both halophilic and halotolerant actinomycetes. The distribution of halophilic actinomycetes was also found to be related to sample sources.
RNA degradation in bacteria, once thought to be a pathway whose only function was to scavenge nucleotides for the re-synthesis of RNA’s, is now known to be a complex, carefully regulated pathway that involves a number of key enzymes acting in concert. In Escherichia coli some of those enzymes are organized into a supramolecular complex that participates in the degradation of cellular RNA’s and it is now clear that RNA degradation represents an important intracellular mechanism for the regulation of gene expression in bacteria. In what follows, I will briefly review what is known about RNA degradation in E. coli and Bacillus subtilis and then discuss the relationships between RNA degradation, gene expression and antibiotic synthesis in the genus Streptomyces.