Abstract
Streptomyces coelicolor is a model actinomycete that is well known for the diversity of its secondary metabolism and its complex life cycle. As a soil inhabitant, it is exposed to heterogeneous and frequently changing environmental circumstances. In the present work, we studied the effect of diverse growth conditions and phosphate depletion on its lipid profile and the relationship between membrane lipid composition and development in S. coelicolor. The lipid profile from cultures grown on solid media, which is closer to the natural habitat of this microorganism, does not resemble the previously reported lipid composition from liquid grown cultures of S. coelicolor. Wide variations were also observed across different media, growth phases, and developmental stages indicating active membrane remodeling. Ornithine lipids (OL) are phosphorus-free polar lipids that were accumulated mainly during sporulation stages, but were also major components of the membrane under phosphorus limitation. In contrast, phosphatidylethanolamine, which had been reported as one of the major polar lipids in the genus Streptomyces, is almost absent under these conditions. We identified one of the genes responsible for the synthesis of OL (SCO0921) and found that its inactivation causes the absence of OL, precocious morphological development and actinorhodin production. Our observations indicate a remarkable plasticity of the membrane composition in this bacterial species, reveal a higher metabolic complexity than expected, and suggest a relationship between cytoplasmic membrane components and the differentiation programs in S. coelicolor.
Highlights
Streptomyces coelicolor is a soil dwelling actinomycete that has been for decades a model for the study of secondary metabolism and differentiation in Gram-positive bacteria
The previous characterizations of the S. coelicolor lipid profile had been performed in the latter conditions (SandovalCalderón et al, 2009; Jyothikumar et al, 2012), we wondered if S. coelicolor grown on solid medium would present a different membrane lipid composition compared to bacteria grown in liquid medium
S. coelicolor grown in solid YEME medium presented barely detectable amounts of PE (3) and CL (1), and accumulated instead MLCL (4) and high amounts of DLCL (5) – putative derivatives of CL (1), in addition to phosphatidylinositol mannosides (PIMs) (7), PI (6) and an unidentified phospholipid (Figure 2, top right panel)
Summary
Streptomyces coelicolor is a soil dwelling actinomycete that has been for decades a model for the study of secondary metabolism and differentiation in Gram-positive bacteria. It displays a complex life cycle that involves both morphological and physiological differentiation. Morphological differentiation is a coordinated process that involves an interplay between environmental stimuli such as nutritional cues, physiological conditions and extracellular signaling (McCormick and Flärdh, 2012). Extracellular signaling is relevant in different Streptomyces species; A-factor is a well-studied γ-butyrolactone that regulates both morphological differentiation and antibiotic biosynthesis in Streptomyces griseus (Horinouchi et al, 2001). The products of extracellular proteolytic activity may be part of the complex signaling network underlying the coordination of morphological development (Chater et al, 2010)
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