Bacteriology Lecture Notes - PDF

B AC T E L R I O L O G Y Lecture No 2 4. Cytoplasmic Membrane A layer of phospholipids and proteins, encloses the interior of the bacterium, regulating the flow of materials in and out of the cell. This is a structural trait bacteria share with all other living cells. Cytoplasmic Membrane F...

B AC T E L R I O L O G Y Lecture No 2 4. Cytoplasmic Membrane A layer of phospholipids and proteins, encloses the interior of the bacterium, regulating the flow of materials in and out of the cell. This is a structural trait bacteria share with all other living cells. Cytoplasmic Membrane Functions active transport and selective diffusion of molecules and solutes in and out of the cell. Electron transport and oxidative phosphorylation, in aerobic species. Synthesis of cell wall precursors. Secretion of enzymes and toxins. Supporting the receptors and other proteins of the chemotactic and sensory transduction systems.  5. Cytoplasm The cell envelope encases the cytoplasm and all its components. It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids. Unlike the eukaryotic (true) cells, bacteria do not have a membrane enclosed nucleus. All the other cellular components are scattered throughout the cytoplasm.  Nuclear material or nucleoid Bacterial DNA comprises a single, supercoiled, circular chromosome. Contains about 2000 genes, approximately 1mm long in the unfolded state. (It is analogous to a single, haploid chromosome.) During cell division, it undergoes semiconservative replication bidirectionally from a fixed point.  Ribosome Ribosomes are the sites of protein synthesis. Bacterial ribosomes differ from those of eukaryotic cells in both size and chemical composition. They are organized in units of 70S, compared with eukaryotic ribosomes of 80S. These differences are the basis of the selective action of some antibiotics that inhibit bacterial, but not human, protein β- synthesis.  Plasmids They are small, extrachromosomal genetic structures made of a circular piece of DNA. Unlike the chromosome, they are not involved in reproduction. Plasmids replicate independently of the chromosome and, while not essential for survival. Plasmids are passed on to other bacteria through two means. For most plasmid types, copies in the cytoplasm are passed on to daughter cells during binary fission. Other types of plasmids, form a tubelike structure at the surface called a pilus that passes copies of the plasmid to other bacteria during conjugation, a process by which bacteria exchange genetic information. Plasmids have been shown to be instrumental in the transmission of special properties, such as antibiotic drug resistance, and virulence factors necessary for infection. Structures external to the cell wall 1. Flagella Flagella (singular, flagellum) are hairlike structures that provide a means of locomotion for bacteria. They can be found at either or both ends of a bacterium or all over its surface. The flagella beat in a propeller-like motion to help the bacterium move toward nutrients; away from toxic chemicals; or, in the case of the photosynthetic cyanobacteria; toward the light. 2. Pili They are small hairlike projections emerging from the outside cell surface. shorter than flagella They assist the bacteria in attaching to other cells and surfaces, such as teeth, intestines, and rocks. Specialized pili are used for conjugation, during which two bacteria exchange fragments of plasmid DNA. Bacterial Spores Spores are formed in response to adverse conditions by the medically important bacteria that belong to the genus Bacillus (which includes the agent of anthrax) and the genus Clostridium (which includes the agents of tetanus and botulism). bacteria sporulate (form spores) when nutrients, such as sources of carbon and nitrogen, are scarce. The spore develops at the expense of the vegetative cell and contains; Bacterial DNA, a small amount of cytoplasm, cell membrane, peptidoglycan, very little water and, most importantly, a thick, keratin-like coat. Once formed, the spore is metabolically inert and can remain dormant for many years.  When appropriate conditions supervene (i.e., water, nutrients) Enzymatic degradation of the coat. The spore transforms itself into a metabolizing, reproducing bacterial cell once again Search and discuss later Clinical significance of bacterial spores, with examples. What is archaea, Core microbiome; oral microbiota. define, detection, is it good or evil. How do organisms get their names? Key facts The main groups of microbes are algae, protozoa, fungi, bacteria and viruses. All living cells are either prokaryotic (Archaea and Bacteria) or eukaryotic. Eukaryotes have a nucleus, organelles such as mitochondria and complex internal membranes (e.g., fungi, human cells). Bacteria are divided into two major classes according to staining characteristics: Gram-positive (purple) and Gram negative (pink). Key facts Bacterial cytoplasm contains chromosomal nuclear material: nucleoid, ribosomes. Structures external to the cell wall of bacteria are flagella (whip-like filaments), fimbriae or pili (fine, short, hair-like filaments), and capsule. Flagella are used for movement, the fimbriae and pili for adhesion. Cell wall peptidoglycan is common to both Gram-positive and Gram-negative bacteria but thicker in the former; it gives rigidity and shape to the organism. Spore formation or sporulation is a response to adverse conditions in Bacillus spp. and Clostridium spp.