Higher order structural organization of the nucleoid in the thiobacteriumThiosphaera pantotropha

Cytoskeletal Elements in Bacteria Mycoplasma pneumoniae, Thermoanaerobacterium sp., and Escherichia coli as Revealed by Electron Microscopy

Recently, electron microscopic studies on the eubacteria Mycoplasma pneumoniae, Thermoanaerobacterium sp., and Escherichia coli have revealed the existence of cytoskeletal elements so far unknown in prokaryotes. The wall-less bacterium M. pneumoniae contains, in close vicinity to the inner face of the cytoplasmic membrane, a helically organized lining composed of protein elements that form a regular network of meshes that encloses the entire cytoplasm. Numerous regularly spaced pin-like structural elements, the stalks with terminal knobs, connect the lining with the cytoplasmic membrane. In this bacterium, a specific rod-like structural element is located in the tip region. Occasionally, it is bent or twisted. It consists of two matching blade-like sub-elements. A number of parallel linkers, extending from the edges of the rod, make contact with the lining. The proximal end of the rod is attached to a wheel-like complex. Fibrils originating from the wheel cross the cytoplasm and make contact with the lining. E. coli contains a similar helically organized lining close to the inner face of the cytoplasmic membrane. Groups of ribosomes (polysomes) were seen to be attached to the helical elements of the lining. A feature that is common to both bacteria and to Thermoanaerobacterium sp. appears to be that the lining and the fibrils crossing the cytoplasm contain a high number of copies of the bacterial elongation factor Tu (EF-Tu). This indicates that this protein may play an important role as a structural element in bacterial cytoskeletons. This notion was supported by experiments in which the cytoskeleton in E. coli was destabilized by induced expression of truncated EF-Tu, with the consequence of cell lysis, and by the finding that in vitro polymerization of monomeric EF-Tu into protofilaments was hindered in a mixture of full-size EF-Tu and truncated EF-Tu consisting of domain 3 only. Current research and developmental efforts are aimed at the design of a new class of antibacterial drugs, acting by destabilization of the EF-Tu-containing bacterial cytoskeleton, and of an innovative mode of inducible lysis of recombinant bacteria by controlled destabilization of the EF-Tu-containing cytoskeleton.

Principles of macromolecular organization and cell function in bacteria and archaea

Structural organization of the cytoplasm by compartmentation is a well established fact for the eukaryotic cell. In prokaryotes, compartmentation is less obvious. Most prokaryotes do not need intracytoplasmic membranes to maintain their vital functions. This review, especially dealing with prokaryotes, will point out that compartmentation in prokaryotes is present, but not only achieved by membranes. Besides membranes, the nucleoid, multienzyme complexes and metabolons, storage granules, and cytoskeletal elements are involved in compartmentation. In this respect, the organization of the cytoplasm of prokaryotes is similar to that in the eukaryotic cell. Compartmentation influences properties of water in cells.

Cloning and sequencing the genes encoding uptake-hydrogenase subunits of Rhodocyclus gelatinosus

Rhodocyclus gelatinosus grew photosynthetically in the light and consumed H2 at a rate of about 665 nmol/min per mg protein. The uptake-hydrogenase (H2ase) was found to be membrane bound and insensitive to inhibition by CO. The structural genes of R. gelatinosus uptake-H2ase were isolated from a 40 kb cosmid gene library of R. gelatinosus DNA by hybridization with the structural genes of uptake-H2ase of Bradyrhizobium japonicum and Rhodobacter capsulatus. The R. gelatinosus genes were localized on two overlapping DNA restriction fragments subcloned into pUC18. Two open reading frames (ORF1 and ORF2) were observed. ORF1 contained 1080 nucleotides and encoded a 39.4 kDa protein. ORF2 had 1854 nucleotides and encoded a 68.5 kDa protein. Amino acid sequence analysis suggested that ORF1 and ORF2 corresponded to the small (HupS) and large (HupL) subunits, respectively, of R. gelatinosus uptake-H2ase. ORF1 was approximately 80% homologous with the small, and ORF2 was maximally 68% homologous with the large subunit of typical membrane-bound uptake-H2ases.