CELL COMPARTMENTALIZATION AND CELL DIVISION IN PHYLA PLANCTOMYCETES AND VERRUCOMICROBIA

Kuo-chang Lee (2010). CELL COMPARTMENTALIZATION AND CELL DIVISION IN PHYLA PLANCTOMYCETES AND VERRUCOMICROBIA PhD Thesis, School of Chemistry & Molecular Bioscience, The University of Queensland.

       
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Author Kuo-chang Lee
Thesis Title CELL COMPARTMENTALIZATION AND CELL DIVISION IN PHYLA PLANCTOMYCETES AND VERRUCOMICROBIA
School, Centre or Institute School of Chemistry & Molecular Bioscience
Institution The University of Queensland
Publication date 2010-08
Thesis type PhD Thesis
Supervisor Professor John A. Fuerst
Associate Professor Roy Hall
Total pages 204
Total colour pages 23
Total black and white pages 181
Subjects 06 Biological Sciences
Abstract/Summary Members of phylum Planctomycetes of the domain Bacteria are distinctive budding peptidoglycan-less and compartmentalized bacteria from aquatic and soil habitats. It has been previously established that all planctomycetes share a cell plan in which the nucleoid DNA is enclosed by at least one membrane, the intracytoplasmic membrane (ICM), forming a major cell organelle, the pirellulosome. The shared cell structure of planctomycetes also involves a ribosome-free region of the cytoplasm between cytoplasmic membrane and ICM termed the ‘paryphoplasm’. The genomic DNA of Gemmata obscuriglobus within the pirellulosome is further enclosed by two membranes forming an envelope surrounding a nuclear body containing the nucleoid and its DNA. From phase contrast microscopy and TEM of thin-section of cells of G. obscuriglobus prepared by high-pressure freezing techniques, a model for the cell cycle of G. obscuriglobus has been derived in which a mother cell forms a small bud with a narrow neck relative to the mother cell diameter, and this bud gradually enlarges until it is similar in size to the mother cell, a stage which then lasts for a time considerably longer than other stages of cell division. Both the mother cell and the finally released bud are capable of further cell division. During cell division, the earliest visible bud stage does not possess DNA and a naked nucleoid is transferred into the bud when the bud is more matured. This stage is followed by the formation of a double-membrane nucleoid envelope surrounding the nucleoid. The new nucleoid envelope of the bud is derived from existing intracellular membranes of both mother and daughter cells where the inner-membrane of the nucleoid envelope originates from the mother cell ICM and the outer-membrane of the same envelope is derived from the bud ICM. We have extended knowledge of the occurrence of the shared planctomycete cell plan to newly described planctomycetes including Zavarzinella formosa and Ellin6207. These two strains share the major features of the common planctomycete cell plan, but also display unique characteristics. So in Ellin6207 there are unique nucleoid-associated bodies and condensed bodies within the nucleoid, while in Zavarzinella formosa, membrane-bounded vesicle-like entities are situated in the paryphoplasm region, a structural characteristic we have not observed in Gemmata strains fixed by the same methods. The phylum Verrucomicrobia forms a distinct phylogenetically divergent phylum within the domain Bacteria, characterized by members widely distributed in soil and aquatic habitats. A superphylum called the PVC superphylum has been proposed by Wagner and Horn (2006) which comprises mainly the phyla Planctomycetes, Verrucomicrobia and Chlamydiae. Based on the proposed relationships between the three lineages, we hypothesized that members of Planctomycetes and Verrucomicrobia might share a similar ultrastructural plan. Four members of the phylum Verrucomicrobia were examined including Verrucomicrobium spinosum, Prosthecobacter dejongeii, Chthoniobacter flavus and Ellin514. TEM results show that these strains share a basic cell plan analogous to that found in members of the phylum Planctomycetes. This cell plan is in known planctomycetes characterized by compartmentalization of the cell cytoplasm by a major cell organelle bounded by a single membrane containing all the cell DNA in a fibrillar condensed nucleoid, as well as ribosome-like particles. This major membrane-bounded organelle is equivalent to the pirellulosome of planctomycetes, and its bounding membrane is equivalent to the ICM defined in planctomycetes as surrounding the pirellulosome. Consistent with the structural analogies between verrucomicrobia and planctomycetes, the ribosome-free region between the intracytoplasmic membrane of the pirellulosome and the cytoplasmic membrane in verrucomicrobia can be considered equivalent to the paryphoplasm of planctomycetes. We have found that this planctomycete cell plan is present in at least 3 of the 6 subdivisions of the Verrucomicrobia, suggesting that the common ancestor of the verrucomicrobial phylum was also compartmentalized and possessed such a plan. The presence of this compartmentalized cell plan in both phylum Planctomycetes and phylum Verrucomicrobia suggests that the last common ancestor of these phyla was also compartmentalized. Cell compartmentalization of this type may thus have significant meaning phylogenetically, and can act as a clue to the meaning of deeper evolutionary relationships between bacterial phyla. Its occurrence in a second phylum of domain Bacteria extends and reinforces the challenge to the concept of prokaryotic organization already posed by planctomycete cell organization. Members of the phylum Planctomycetes have been shown to lack FtsZ, a bacterial tubulin homologue cell division protein that is conserved virtually in all bacteria, which raises the question of which proteins are responsible for cell division in the members of this group. FtsK is a multifunctional protein that couples cell division and chromosome segregation in Escherichia coli. Nearly all FtsK proteins contain an N-terminal transmembrane domain essential for septum formation, a C-terminal P-loop ATPase and FtsK gamma DNA-binding domains responsible for chromosome segregation and DNA translocation and a central FtsKL domain that is highly divergent between bacterial species and differ in size with functions which have yet to be defined. G. obscuriglobus ftsK gene sequence (2433 bases) was successfully retrieved from the draft genome at TIGR database and the open reading frame of the protein was detected using the NCBI ORF finder program. G. obscuriglobus FtsK has been predicted from our analysis to possess 4 possible transmembrane helices at the N-terminus region and a large hydrophilic C-terminal domain. G. obscuriglobus FtsK possesses two conserved domains at the C-terminal region including a P-loop NTPase superfamily domain and an FtsK gamma DNA-binding domain. These two domains are also conserved in all other bacterial FtsKs. Immunogold labelling showed that FtsK within the pirellulosome is associated mainly with the DNA of the condensed nucleoid but sometimes appears associated with DNA in the process of transfer during cell division, which suggests a role in DNA transfer consistent with that of SpoIIIE protein found in B. subtilis. FtsK of G. obscuriglobus is localized in a specific major membrane-bounded compartment, the pirellulosome, suggesting a functional role in compartmentalization that is unique from FtsK in other organisms. This is consistent with a functional role for the pirellulosome, as indicated by the membrane-delimited localisation within the pirellulosome of a protein of significance for cell division or chromosome segregation.
Keyword planctomycetes, verrucomicrobia, ftsk, cell division, compartmentalization, PVC superphylum, high-pressure freezing, pirellulosome, paryphoplasm, nucleoid
Additional Notes pages that should be printed in colour: 31, 33, 40-41, 50, 64-65, 79, 109, 122, 125-126, 128, 132, 138, 145, 177-181, 187, 190 pages that should be printed in landscape: 50-51

 
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Created: Tue, 28 Sep 2010, 16:18:00 EST by Mr Kuo-chang Lee on behalf of Library - Information Access Service