![]() ![]() Spores of these organisms not only guard genetic information during unfavorable conditions, but are also adapted to wind dispersal and may remain airborne for long periods. Both, streptomycetes and molds produce large numbers of small hydrophobic spores with similar properties both contain, for example, a relatively thick coat ( Briza et al., 1990 Pammer et al., 1992 Neiman, 2005), protective small molecules including sugars (such as trehalose, see below), and heat shock proteins ( Wyatt et al., 2013). Penicillium species, for example, produce conidiophores (analogous to streptomycete aerial hyphae, see below) that bear individually constricted conidiospores ( Foster et al., 1945). The streptomycete arthrospores, on the other hand, are more reminiscent of the spores of eukaryotic fungi, possibly due to their convergent evolution in the soil environment. All these features contribute to the overall robust endospore resistance. The well-studied endospores of Bacillus subtilis contain high levels of dipicolinic acid in chelation with divalent cations (Ca 2+) and extremely stable small spore proteins ( Setlow et al., 2006). Their abilities to survive harsh conditions result from multi-layered surface structures and extremely low water content ( Setlow et al., 2006 Henriques and Moran, 2007). The endospores exhibit striking resistance to a wide range of environmental stresses, such as heat, desiccation, and ultraviolet radiation ( Setlow, 2007 Galperin et al., 2012). Arthrospores significantly differ from the endospores of Bacilli and Clostridia in morphology and function. Several bacterial clades living in soil, such as Actinomyces, Streptomyces, and Micromonospora, differentiate into dormant fungi-like uninucleoid spores (arthrospores or exospores). In the dormant state, cells arrest their growth, discontinue replication and transform themselves into metabolically inactive (or with limited activity), widely resistant forms. ![]() ![]() An important survival strategy for many bacteria and fungi in the face of such physiological stresses is the cells’ transition into a dormant state. Soil microorganisms are exposed to periodic nutrient exhaustions and various abiotic and biotic stresses that inhibit growth. This review summarizes our current knowledge about the germination process in Streptomyces, while focusing on the aforementioned points. There are several aspects of germination that may attract our attention: (1) Dormant spores are strikingly well-prepared for the future metabolic restart they possess stable transcriptome, hydrolytic enzymes, chaperones, and other required macromolecules stabilized in a trehalose milieu (2) Germination itself is a specific sequence of events leading to a complete morphological remodeling that include spore swelling, cell wall reconstruction, and eventually germ tube emergences (3) Still not fully unveiled are the strategies that enable the process, including a single cell’s signal transduction and gene expression control, as well as intercellular communication and the probability of germination across the whole population. Still, germination represents a system of transformation from metabolic zero point to a new living lap. Whereas their mycelial life – connected with spore formation and antibiotic production – is deeply investigated, spore germination as the counterpoint in their life cycle has received much less attention. The complex development undergone by Streptomyces encompasses transitions from vegetative mycelial forms to reproductive aerial hyphae that differentiate into chains of single-celled spores. 3Institute of Microbiology of the Czech Academy of Sciences, Prague, Czechia. ![]()
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