Gene-expression analyses of acidic pH shock effects on actinorhodin production in Streptomyces coelicolor A3(2)

Abstract

Actinorhodin production is markedly enhanced when an acidic pH shock is applied to a surface-grown culture of Streptomyces coelicolor A3(2). For an in-depth study of this phenomenon, transcriptional analyses by DNA microarras, and RT-PCR and proteomic analysis methods were performed. Investigated were expression levels of the regulators and enzymes responsible for signal transduction and actinorhodin biosynthesis, and enzymes involved in some major metabolic pathways such as glycolysis, the tricarboxylic acid cycle, fatty acid metabolism, and the pentose phosphate pathway (PPP). In addition, the effects of pH shock on the stress response related genes to investigate the relationship between acidic pH shock and other shocks, through transcriptional and proteomic analysis also. The regulators PkaG, AfsR, AfsS and/or another unidentified regulator and ActII-ORF4, in sequence, were observed to be activated by pH shock. In addition, a number of genes associated with actinorhodin production and secretion, and the major central metabolic pathways investigated were observed to be up-regulated with pH shock. Fatty acid degradation was particularly promoted by pH shock, while fatty acid biosynthesis, consuming acetyl-CoA was suppressed; it is envisaged that this enriches the precursor pool (acetyl-CoA) and building blocks for actinorhodin biosynthesis. Furthermore, glucose 6-phosphate dehydrogenases (zwf and zwf2), key enzymes to initiate the PPP, were highly activated by pH shock, enriching the NADPH pool for biosynthesis in general. It is deduced that these metabolic changes caused by pH shock have positively contributed to the stimulation of actinorhodin biosynthesis in a concerted manner. A number of shock related proteins were observed to be induced by acidic pH shock. Well known sigma factors of sigH (by heat shock), sigR (by oxidative stress), and sigB (by osmotic stress) which play a major role in the secondary metabolism, were all strongly upregulated in th...