Keys to Eukaryality: Planctomycetes and Ancestral Evolution of Cellular Complexity

Planctomycetes are known to display compartmentalization via internal membranes, thus resembling eukaryotes. Significantly, the planctomycete Gemmata obscuriglobus has not only a nuclear region surrounded by a double-membrane, but is also capable of protein uptake via endocytosis. In order to clearly analyze implications for homology of their characters with eukaryotes, a correct understanding of planctomycete structure is an essential starting point. Here we outline the major features of such structure necessary for assessing the case for or against homology with eukaryote cell complexity. We consider an evolutionary model for cell organization involving reductive evolution of Planctomycetes from a complex proto-eukaryote-like last universal common ancestor, and evaluate alternative models for origins of the unique planctomycete cell plan. Overall, the structural and molecular evidence is not consistent with convergent evolution of eukaryote-like features in a bacterium and favors a homologous relationship of Planctomycetes and eukaryotes

Undergraduate Research Experiences: a Case Study in promoting Student Engagement through Authentic Scientific Inquiry

Laboratory exercises teach practical skills that form the foundation of scientific research. These classes however, have been ineffective in promoting student engagement in science, as they are often structured around rigid and repetitive protocols. These traditional “cookbook” laboratory classes are not an accurate representation of scientific inquiry, and do not teach students the autonomy required to succeed as a professional scientist. This project directly engaged students in the discovery process by integrating Undergraduate Research Experience (URE) modules into MICR3003, a third year Microbiology course offered at the University of Queensland (UQ). As part of their undergraduate coursework, students conducted inquiry-based experiments to make novel experimental findings, and were assessed on their adherence to professional scientific standards. At the end of the URE, students demonstrated improvements in key experimental, reporting, and analytical skills, as well as an increase in their general interest in science; moreover, the URE participants appreciated the opportunity to collectively experience an immersive undergraduate research project. Embedding active research projects into the undergraduate curriculum is able to reach a far greater number of students than isolated laboratory internships, and thus is an effective mechanism for increasing exposure for science and providing training for the next generation of scientists

Turning the Table: Plants Consume Microbes as a Source of Nutrients

Interactions between plants and microbes in soil, the final frontier of ecology, determine the availability of nutrients to plants and thereby primary production of terrestrial ecosystems. Nutrient cycling in soils is considered a battle between autotrophs and heterotrophs in which the latter usually outcompete the former, although recent studies have questioned the unconditional reign of microbes on nutrient cycles and the plants' dependence on microbes for breakdown of organic matter. Here we present evidence indicative of a more active role of plants in nutrient cycling than currently considered. Using fluorescent-labeled non-pathogenic and non-symbiotic strains of a bacterium and a fungus (Escherichia coli and Saccharomyces cerevisiae, respectively), we demonstrate that microbes enter root cells and are subsequently digested to release nitrogen that is used in shoots. Extensive modifications of root cell walls, as substantiated by cell wall outgrowth and induction of genes encoding cell wall synthesizing, loosening and degrading enzymes, may facilitate the uptake of microbes into root cells. Our study provides further evidence that the autotrophy of plants has a heterotrophic constituent which could explain the presence of root-inhabiting microbes of unknown ecological function. Our discovery has implications for soil ecology and applications including future sustainable agriculture with efficient nutrient cycles

Planctomycetes: their evolutionary implications for models for origins of eukaryotes and the eukaryote nucleus and endomembranes

Planctomycetes and their relatives in the PVC superphylum have significant implications for evolution of the diversity of bacterial and eukaryotic cell organisation. The compartmentalisation via internal membranes of an underlying plan shared by planctomycetes and by members of phyla Verrucomicrobia and Lentisphaerae within the PVC superphylum implies phylogenetic meaning to such structure. It is likely that the common ancestor of PVC superphylum members possessed such compartmentalisation. Compartmentalisation in PVC bacteria, especially within the Gemmata clade where the nucleoid is bounded by an envelope of two membranes, has implications for theories of the origin of the eukaryotic nucleus, suggesting autogenous theories should be considered seriously as major alternatives to those depending on early fusions between Archaea and Bacteria domains. Explanations for the origin of PVC compartmentalisation are considered here, as well as their implications for molecular correlates of such compartmentalisation, and their correlates with an integrated cell biology that may be an analogue or even a homologue of an ancient eukaryote cell biology. PVC bacteria can form major experimental models for exploring what such a cell biology might have looked like

Nested bacterial boxes: nuclear and other intracellular compartments in planctomycetes

Bacteria in the phylum Planctomycetes and some related phyla challenge our concept of the typical bacterium as consisting of cells without internal compartments or membrane-bounded organelles. Cells of all species of planctomycetes examined consist of at least two major compartments, and there are two other types of compartmentation in which a third compartment is formed either by a double-membrane envelope around the nucleoid in the case of the aerobic Gemmata obscuriglobus or by a single but potentially energized membrane in the case of the anaerobic ammonium-oxidizing anammox planctomycetes. We examine here the nature of these planctomycete compartments in relation to function and their relationship to the endomembranes defining them, and discuss the implications of the remarkable compartment-confined process of protein uptake in Gemmata, which resembles receptor- and clathrin-mediated endocytosis of eukaryotes. Planctomycetes have implications for our understanding of the evolution of membrane-bounded organelles, of endomembranes, transport across endomembranes and membrane trafficking, and for how the complexity of a eukaryote style of cell organization could have originated

Cell compartmentalization and endocytosis in planctomycetes: structure and function in complex bacteria

Planctomycetes are unique among the domain Bacteria in possessing cells with a complex plan defined by internal membranes forming separated compartments within the cell. They also possess other unique features such as cell walls composed of protein as a major polymer instead of the peptidoglycan typical of other bacteria. All species examined display an underlying shared cell organization in which an internal intracytoplasmic membrane separates two major cell compartments, an outer ribosome-free paryphoplasm and a more central ribosome-containing pirellulosome. Some planctomycete species have three compartments, where further membranes within the pirellulosome define another compartment, the anammoxosome in anammox planctomycetes and the membrane-bounded nuclear body in Gemmata obscuriglobus. Compartments are preserved when new cells are formed during division. Functional features which are correlated with structural compartmentalization in planctomycetes include in G. obscuriglobus the ability to take up proteins within the paryphoplasm of the cell by a mechanism similar to receptor-mediated endocytosis of eukaryotes. Novel molecular and cell biology features for bacteria can be predicted to accompany such structural and functional complexity and are discussed here

Low-frequency common fragile sites: Link to neuropsychiatric disorders?

Common fragile sites are unstable chromosomal regions that predispose chromosomes to breakage and rearrangements. Recombinogenic DNA sequences encompassing these sites may contribute to both germinal and somatic genomic mutations, and the genomic instability at these regions might cause severe inherited disorders or predispose to cancer. In this review, we discuss the characterization of common fragile site FRA13A within the neurobeachin gene, which is involved in development and function of the central nervous system. We raise the possibility of an implication of common fragile sites in neuropsychiatric disorders and overview previous and recent reports concerning individual variability of expression of common fragile sites in human populations

Suppression of polyploidy by the BRCA2 protein

Mounting evidence implicates BRCA2 not only in maintenance of genome integrity but also in cell-cycle checkpoints. However, the contribution of BRCA2 in the checkpoints is still far from being understood. Here, we demonstrate that breast cancer cells MX-1 are unable to maintain genome integrity, which results in gross polyploidization. We generated MX-1 clones, stably expressing BRCA2, and found that BRCA2 acts to suppress polyploidy. Compared with MX-1, the ectopically BRCA2-expressing cells had different intracellular levels of Aurora A, Aurora B, p21, E2F-1, and pRb, suggesting a BRCA2-mediated suppression of polyploidy via stabilization of the checkpoint proteins levels