CdgB Regulates Morphological Differentiation and Toyocamycin Production in Streptomyces diastatochromogenes 1628.

Bis (3',5')-cyclic diguanylic acid (c-di-GMP) is a ubiquitous second messenger that controls several metabolic pathways in bacteria. In Streptomyces , c-di-GMP is associated with morphological differentiation, which is related to secondary metabolite production. In this study, we identified and characterized a diguanylate cyclase (DGC), CdgB, from Streptomyces diastatochromogenes 1628, which may be involved in c-di-GMP synthesis, through genetic and biochemical analyses. To further investigate the role of CdgB, the cdgB -deleted mutant strain Δ- cdgB and the cdgB -overexpressing mutant strain O- cdgB were constructed by genetic engineering. A phenotypic analysis revealed that the O- cdgB colonies exhibited reduced mycelium formation, whereas the Δ-cdgB colonies displayed wrinkled surfaces and shriveled mycelia. Notably, O- cdgB demonstrated a significant increase in the toyocamycin (TM) yield by 47.3%, from 253 to 374 mg/L, within 10 days. This increase was accompanied by a 6.7% elevation in the intracellular concentration of c-di-GMP and a higher transcriptional level of the toy cluster within four days. Conversely, Δ- cdgB showed a lower c-di-GMP concentration (reduced by 6.2%) in vivo and a reduced toyocamycin production (decreased by 28.9%, from 253 to 180 mg/L) after 10 days. In addition, S. diastatochromogenes 1628 exhibited a slightly higher inhibitory effect against Fusarium oxysporum f. sp. cucumerinum and Rhizoctonia solani compared to Δ- cdgB , but a lower inhibition rate than that of O- cdgB . The results imply that CdgB provides a foundational function for metabolism and the activation of secondary metabolism in S. diastatochromogenes 1628.