Phosphoinositides Are Involved in Control of the Glucose-Dependent Growth Resumption That Follows the Transition Phase inStreptomyces lividans

Abstract

The interruption of the sblA gene of Streptomyces lividans was previously shown to lead to relief of glucose repression of the normally strongly glucose-repressed ␣-amylase gene. In addition to this relief, an early entry into stationary phase was observed when cells were grown in a minimal medium containing glucose as the main carbon source. In this study, we established that this mutant does not resume growth after the transition phase when cultured in the complex glucose-rich liquid medium R2YE and sporulates much earlier than the wild-type strain when plated on solid R2YE. These phenotypic differences, which were abolished when glucose was omitted from the R2YE medium, correlated with a reduced glucose uptake ability of the sblA mutant strain. sblA was shown to encode a bifunctional enzyme possessing phospholipase C-like and phosphoinositide phosphatase activities. The cleavage of phosphoinositides by SblA seems necessary to trigger the glucose-dependent renewed growth that follows the transition phase. The transient expression of sblA that takes place just before the transition phase is consistent with a regulatory role for this gene during the late stages of growth. The tight temporal control of sblA expression was shown to depend on two operator sites. One, located just upstream of the ؊35 promoter region, likely constitutes a repressor binding site. The other, located 170 bp downstream of the GTG sblA translational start codon, may be involved in the regulation of the degradation of the sblA transcript. This study suggests that phosphoinositides constitute important regulatory molecules in Streptomyces, as they do in eukaryotes.

Mycelium Differentiation and Antibiotic Production in Submerged Cultures ofStreptomyces coelicolor

“…Most authors assume that no differentiation processes occur in submerged cultures and that antibiotics are produced by the substrate mycelium when it reaches the stationary phase (13,25,43,46,61,67). On the other hand, it is known that mycelial morphology correlates with the production of secondary metabolites, and most authors state that cellular aggregation, and therefore pellet and clump formation, is fundamental to obtaining good production.…”

“…There is a general consensus that a transient arrest of growth characterizes Streptomyces grown in submerged cultures (13,25,43,46,52,67). This growth arrest precedes antibiotic production (28) and can activate antibiotic biosynthetic genes (31,43), antibiotic resistance genes (50), and stress response stimulons (48), as well as arrest of ribosomal protein synthesis (3).…”

Carbon source regulation of antibiotic production

“…114 With regard to bldG, it has been proposed that this gene encodes a putative anti-anti-sigma factor that might control transcription of both aerial mycelia formation and antibiotic formation. 120 Using transposon mutagenesis, Chouayekh et al 121 isolated S. lividans TK24 mutants the a-amylase expression of which was resistant to glucose catabolite repression. Mutant characterization showed interruption of the sblA gene (equivalent to SCO0479 of S. coelicolor).…”

Importance and regulation of inositol biosynthesis during growth and differentiation of Streptomyces

“…This implies that PI and its derivatives are probably also made in S. coelicolor. Indeed, in the very closely related Streptomyces lividans , PI makes up about 10–15% of the total phospholipid (Chouayekh et al ., 2007), and phosphatidylinositol mannosides and dilyso‐cardiolipin‐phosphatidylinositol (DLCL‐PI) have been found as a membrane component in S. hygroscopicus (Hoischen et al ., 1997), so PI synthesis is probably a general attribute of the genus (these genes are also conserved in many other actinomycete genomes). Studies of SCO1527 are in progress.…”