2005; Gomelsky et al. 2008). The data indicate that the LHII antenna complexes are severely diminished relative to the wild type. The correlation between MK0683 the reduction or lack of LHII and the presence of

tubular structures has been noted by Selleck GSI-IX others (Kiley et al. 1988; Hunter et al. 1988; Sabaty et al. 1994; Siebert et al. 2004). But we believe this is the first report of such aberrant structures in regulatory gene mutants. Importantly, the available information regarding regulation of PS gene expression by PrrA and PpsR does not explain why LHII is absent while LHI and RC are present (Gomelsky et al. 2008). It implies that other genes necessary for proper ICM development, such as assembly factors required for LHII formation, are also inappropriately (not) expressed in the absence of PrrA and PpsR. Ultrastructure of R. sphaeroides and R. capsulatus wild type and fnrL mutant bacteria FnrL belongs to the Fnr–Crp protein family (Zeilstra-Ryalls and Kaplan 1995). All members are characterized by the presence of an effector

domain located within the N-terminal SN-38 manufacturer region and a DNA binding domain located within the C-terminal region. For FnrL, the effector domain is thought to contain an oxygen-labile 4Fe-4S cluster whose presence is required for the protein to be properly configured for DNA binding. Thus, the protein regulates gene transcription when oxygen is limiting. While FnrL is essential for all anaerobic growth of R. sphaeroides 2.4.1, both in the light and in the dark with DMSO (Zeilstra-Ryalls and Kaplan 1995), the reason for this is not yet resolved (detailed in Gomelsky and Zeilstra-Ryalls 2013). Thin sections of cells cultured under low-oxygen conditions, which are permissive for growth of FnrL null mutant bacteria but also support some FnrL regulatory activity (Roh and Kaplan 2002), were examined using TEM (Fig. 4A). In contrast to the typical high density of ICM observed in the thin sections of wild type

cells, approximately 3-oxoacyl-(acyl-carrier-protein) reductase 5–10 ICM-like structures per cell were seen in the sections of the fnrL null mutant JZ1678. While the number of these structures is approximately the same as that seen in sections of the PrrA− mutant bacteria cultured under low-oxygen conditions (Fig. 1A), spectral complexes are detectable in cells lacking FnrL (Zeilstra-Ryalls et al. 1997), which correlates with regulation of different sets of genes by these two transcription factors (Gomelsky and Zeilstra-Ryalls 2013), even though both are indispensable for phototrophic growth. Fig. 4 TEM micrographs of thin sections of wild type and mutant strains of R. sphaeroides (A) and R. capsulatus (B) bacteria that had been cultured under low-oxygen conditions. The strains used are as explained in the legends, with details provided in Table 1 Although both R. sphaeroides and R. capsulatus require FnrL for anaerobic–dark growth with DMSO, R.