Two novel homologous proteins of Streptomyces coelicolor and Streptomyces lividans are involved in the formation of the rodlet layer and mediate attachment to a hydrophobic surface

Abstract

Two novel homologous proteins of Streptomyces coelicolor and Streptomyces lividans are involved in the formation of the rodlet layer and mediate attachment to a hydrophobic surface IntroductionStreptomycetes are Gram-positive soil bacteria that colonize moist substrates by forming a branched network of multinucleoid hyphae. At some stage during their life cycle, these bacteria are confronted with a hydrophobic environment. For instance, after a feeding substrate mycelium has been established, hyphae leave the aqueous environment to grow into the hydrophobic air. These aerial hyphae differentiate further by forming chains of uninucleoid cells, which metamorphose into pigmented spores. Spores or hyphae of streptomycetes may also encounter hydrophobic solids such as surfaces of dead or living organisms. When streptomycete hyphae leave their aqueous environment, they change their surface. Hyphae in a moist substrate are hydrophilic, whereas the surfaces of aerial hyphae and spores are hydrophobic.Formation of aerial structures has been best studied in Streptomyces coelicolor (for recent reviews, see Chater, 1998;Kelemen and Buttner, 1998;Wösten and Willey, 2000). Bald (bld) mutants of S. coelicolor were isolated that, when grown on rich medium, are affected in the formation of aerial structures and in the production of a small surface-active peptide called SapB (Willey et al., 1991). Many of these mutants appear to be affected in an extracellular signalling cascade involved in the erection of aerial hyphae (Willey et al., 1993;Nodwell et al., 1996;. Experimental evidence suggests the existence of at least five signalling molecules. It was hypothesized that each signal triggers the synthesis and release of the next signal, ultimately leading to the production and secretion of SapB (Willey et al., 1993;Nodwell et al., 1996). By lowering the water surface tension from 72 to 32 mJ m -2 , SapB enables hyphae to breach the water-air interface to grow into the air (Tillotson et al., 1998).Aerial hyphae and spores of S. coelicolor have several surface layers that make them hydrophobic. One surface layer, called the rodlet layer, has a typical ultrastructure of a mosaic of 8-to 10-nm-wide parallel rods (Wildermuth et al., 1971;Smucker and Pfister, 1978). The nature of the surface layers is not known. SapB is not expected to form one of these layers, as this peptide was localized in the culture medium but could not be detected at the surfaces of aerial structures (Wösten and Willey, 2000). SummaryThe filamentous bacteria Streptomyces coelicolor and Streptomyces lividans exhibit a complex life cycle. After a branched submerged mycelium has been established, aerial hyphae are formed that may septate to form chains of spores. The aerial structures possess several surface layers of unknown nature that make them hydrophobic, one of which is the rodlet layer. We have identified two homologous proteins, RdlA and RdlB, that are involved in the formation of the rodlet layer in both streptomycetes. The rdl genes are expressed in growi...

A novel class of secreted hydrophobic proteins is involved in aerial hyphae formation inStreptomyces coelicolorby forming amyloid-like fibrils

“…In this way, five proteins were identified. They had masses of 5071-5994 Da and hardly stained with CBB or silver in SDS-PAGE, which explains why they were not reported by Claessen et al (2002). Yet, considerable amounts of these proteins are produced.…”

“…Deleting the rdlA and rdlB genes resulted in the absence of the outer rodlet layer but did not affect surface hydrophobicity (Claessen et al 2002). To isolate the molecules that are involved in the surface hydrophobicity of aerial structures, we performed a TFA extraction on SDS-extracted cell walls from a 5-day-old sporulating culture of an S. coelicolor strain in which both rdlA and rdlB were deleted (M145⌬rdlAB).…”

“…RdlA and RdlB are secreted into the cell wall of growing aerial hyphae, where they form a highly stable insoluble surface layer. Deletion of both rdl genes resulted in loss of the rodlet layer (Claessen et al 2002). Interestingly, the water-repellent nature of aerial hyphae and spores was not affected, implying the existence of other hydrophobic compounds.…”

“…Aerial hyphae and spores of streptomycetes possess a surface layer, called the rodlet layer, with a typical ultrastructure of a mosaic of 8-10-nm-wide parallel rods (Wildermuth et al 1971;Smucker and Pfister 1978;Claessen et al 2002). Two homologous proteins, the rodlins RdlA and RdlB, are necessary for formation of this layer (Claessen et al 2002).…”

“…Two homologous proteins, the rodlins RdlA and RdlB, are necessary for formation of this layer (Claessen et al 2002). RdlA and RdlB are secreted into the cell wall of growing aerial hyphae, where they form a highly stable insoluble surface layer.…”