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Bacteria and Archea: The Prokaryotes Archae & Bacteria There are almost everywhere !!! They are the most numerous organisms that can be found in all habitats Prokaryotes • • • • Appear approximately 3.5 BYA Were the earliest living organisms Have specialized into all habitats Have all types of metabolism – Origin of aerobic and other types of respiration – Origin of several types of photosynthesis Prokaryotes: Tremendous impact on the Earth • Very few cause diseases • As fixers and decomposers they are essential in geo-chemical cycles • Many form symbiotic relationships with other prokaryotes and eukaryotes • Mitochondria and chloroplasts may be descended from symbiotic bacteria Prokaryotes as compared to eukaryotes: • Typically smaller in size • Lack membrane bound organelles • Most have cell walls – but different chemical composition • Have simpler genomes Morphological Diversity of Prokaryotes • Cells have a diversity of shapes the most common being – spheres (cocci) – rods (bacilli) – helices (spirilla and spirochetes). • Prokaryotes are generally single-celled – some aggregate into two-celled to several celled groups – Some have specialized functions, heterocysts in Anabaena. • Fig 27.3 Fig. 27-16 Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Domain Archaea Korarcheotes Domain Eukarya Eukaryotes Nanoarchaeotes Proteobacteria Spirochetes Cyanobacteria Gram-positive bacteria Domain Bacteria Chlamydias Prokaryote Cell walls: • Cell walls: – Maintain the cell shape. – Protect the cell. – Prevent the cell from bursting in a hypotonic environment. • Eubacteria walls contain peptidoglycan – archae cell walls lack peptidoglycan – Peptidoglycan = Modified sugar polymers cross-linked by short polypeptides. Gram Staining • • Gram stain is used to distinguish two groups of eubacteria by structural differences in their cell walls. Gram-positive eubacteria. – Cell walls with large amounts of peptidoglycan that react with Crystal Violet stain Gram-negative eubacteria. • • Have more complex cell walls with less peptidoglycan. An outer lipopolysaccharide-containing membrane blocking the stain from the peptidoglycan. – Stain pink, with safranin • More likely to be disease causing Fig 7.4 Prokaryote cell structure • • Capsule= a gelatinous secretion which provides cells with additional protection Pili = Surface appendages used for adherence to a host (in the case of a pathogen), or for transferring DNA in conjugate. Fig 27.6 Pili The Motility of Prokaryotes: three mechanisms : 1. Swimming with Flagella: differ from eukaryotic: 1. Solid protein 2. Rotate like an oar, rather than whip back and forth 3. The basal apparatus rotation is powered by the diffusion of protons into the cell. Flagella Fig 27.7 2. Filaments – axial filaments are attached to basal motors at either end of the cell. – rotate the cell like a corkscrew. – more effective in viscous substrates than flagella. 3. Gliding – Some bacteria move by gliding through a layer of slimy chemicals secreted by the organism. Taxis= Directed Movement towards or away from a stimulus. • • • • light (phototaxis) chemical (chemotaxis) magnetic field (magnetotaxis) Positive taxis movement toward a stimulus. • Movement away from a stimulus is a negative taxis Non directional Directional Chemotaxis Test Internal Membranous Organization • Some prokaryotes have specialized regions of internal membranes – formed by invaginations of the plasma membranes. Fig 27.8 Specialized membranes Prokaryotic Genomes • Genophore = usually one doublestranded, circular DNA molecule – attached to cell membrane. Plasmid • Smaller independent rings of DNA – “extra genes” -antibiotic resistance or metabolism of unusual nutrients. – Replicate independently of the genophore. – Can be transferred between partners during conjugation – Also found in yeasts, (fungi - eukaryotes) Amount of DNA Genetic Recombination • • • Transformation = external DNA is incorporated by bacterial cells. Conjugation = transfer of genes from one bacterium to another. Transduction = transfer of genes between bacteria via viruses. Conjugation Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Hfr cell A+ A+ F factor F– cell A+ A+ A– Recombinant F– bacterium A– A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome A+ A– A+ Examples of Conjugation Why is antibiotic resistance increasing ? Gene Expression • Prokaryotic and eukaryotic DNA replication and translation are similar – Same genetic code • Bacterial ribosomes smaller and have different protein and RNA content Cell Growth • They divide by Binary Fission. – Genophore attached to plasma membrane – Copies as membrane elongates – New wall forms in between • • • Mitochondria, chloroplasts divide by binary fission too No Mitosis, nor Meiosis. All haploid Binary Fission Fig. 12.10 • Endospore = Resistant cells – Genophore surrounded by a thick wall. Anthrax sp. endospore Major Modes of Nutrition • Energy source (make ATP) – from light (phototrophs), – use chemicals in the environment (chemotrophs). • Carbon source – autotrophs utilize CO2 directly – heterotrophs require at least one organic nutrient as a carbon source. Major Modes of Nutrition: • • • • Photoautotrophs Chemoautotrophs Photoheterotrophs Chemoheterotrophs Table 27-1 Nutritional Diversity Among Chemoheterotrophs • • • Saprobes are decomposers that absorb nutrients from dead organic matter. Parasites are cells that absorb nutrients from body fluids of living hosts compounds that cannot be used as a carbon source by bacteria/fungi are termed non-biodegradable Nitrogen Metabolism In amino acids, nucleotides • Nitrogen fixing bacteria (N2 ->NH3) – In soil, and some plant root nodules • Nitrifying bacteria convert NH3 -> NO2 – In soil, or biotower in treatment plant • Denitrifying bacteria N02 -(Nitrite) or N03 (Nitrate) to atmospheric N2 – In soil, counter-act fertilizers The nitrogen fixing Cyanobacteria are very self-sufficient, they need only light energy, C02, N2, water and a few minerals to grow . Oxygen metabolism • Obligate aerobes • Facultative anaerobes • Obligate anaerobes Three Domains Fig 27.2 Domain Bacteria (Eubacteria) • a very diverse assemblage of organisms. • forms which exhibit every known mode of nutrition and energy metabolism. Domain Archaea (Archaebacteria) • • • • Cell walls lack peptidoglycan. Plasma membranes have a unique lipid composition. RNA polymerase and ribosomal protein are more like those of eukaryotes than of eubacteria Common ancestor with Eukaryotes after split from Bacteria. Domain Archaea (Archaebacteria) • Methanogens. – Use H2 to reduce C02 to CH4 and are strict anaerobes – In Digester at treatment plant • Extreme Halophiles – inhabit high salinity ( 15-20%) environments (e.g. Dead Sea). • Extreme Thermophiles – Live in habitats of 60 - 80C. Hot springs Salt ponds Bacteria and Disease: • Pathogenic= invade, attack host • Opportunistic = Normal inhabitants of the body that become pathogenic • Defense: greatly reduced mortality due to bacterial diseases Cause disease by • Growth and invasion of tissues • Production of a toxin – Exotoxin =Proteins secreted by bacterial cells. – Endotoxin = Toxic component of outer membranes of some gram-negative bacteria Non-Life Bio-particles • Virus: need a living cell to reproduce • Viroids: naked RNA • Prions: rogue free proteins Viral cycle Fig 18.3 Herpes Prions Fig. 18.10