2c), consistent with a critical role for turgor pressure in aerial growth, as previously suggested (Plaskitt & Chater, 1995). In contrast,
the wild type did form aerial structures, which, importantly, was accompanied by the secretion of SapB into the medium (Fig. 2d). We previously showed that the rodlin proteins are not essential for aerial growth under normal conditions (Claessen et al., 2002). Strikingly, development of the S. coelicolor strain lacking rdlA and rdlB was strongly delayed on minimal medium supplemented with sucrose (Fig. 3) or KCl (data not shown). In agreement, increased expression of the rodlin genes was observed in sucrose-containing minimal medium (Fig. S2). Development of the chpABCDH selleck chemicals mutant strain, p38 MAPK signaling lacking five of eight chaplin genes, was also delayed in sucrose-containing medium (Fig. 3). However, the presence of sucrose did not affect the transcript level of chpH (Fig. S2). Taken together, these data show that an intact rodlet layer is important for aerial growth under osmotic stress conditions. On the basis of our data, we propose the following model for aerial growth. At the moment differentiation is initiated, ChpE and ChpH are secreted into the medium. These chaplins assemble into an amphipathic film at the air–water interface. As a result, the water surface tension is dramatically reduced, enabling the growth of
hyphae into the air (Wösten et al., 1999). In a low osmolyte aqueous environment, the turgor pressure of hyphae is sufficient to enable hyphae to breach the chaplin film (Fig. 4a). However, in a high osmolyte aqueous environment, the turgor pressure is reduced and insufficient for hyphae to break through the chaplin film to Nabilone grow into the air. Possibly by intercalation, SapB may change the physical properties of the chaplin film, making it easier to breach. As a consequence, this would enable hyphae to grow
into the air, despite their lower turgor pressure (Fig. 4b and c). This model implies that SapB would also affect the properties of the chaplin film at the surface of the aerial hypha. However, rodlins that are secreted by the aerial hyphae align the chaplin fibrils into rodlets resulting in a rigid film. This rigid film may provide stability of the aerial hypha especially when the turgor pressure in the cell is reduced (Fig. 4d). We thank Hjalmer Permentier and Sander van Leeuwen for technical assistance with MALDI-TOF MS and Justin Nodwell for providing the ramS deletion mutant. This work was financially supported by grants from the Northern Netherlands collaboration initiative (SNN EZ/KOMPAS RM 119) and the Dutch Science Foundation NWO (project 816.02.009). D. Claessen is supported by a Marie Curie Reintegration grant (FP7-PEOPLE-ERG-230944). “
“Bacillus sphaericus has been used with great success in mosquito control programs worldwide.