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Transcript
Lecture VII – Prokaryotes – Dr. Kopeny Delivered 2/6 Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Bacteria and Archaea: The Prokaryotic Domains TER 26 Nitrogen cycle Mycobacterium tuberculosis Color-enhanced images shows rod-shaped bacterium responsible for tuberculosis (Raven et al 2002) Endosymbiotic Theory Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Structure of a Eukaryotic Animal Cell Structure of a Prokaryotic Cell Prokaryotic cells have a simple interior organization compared to Eukaryotes. •Membrane-enclosed nucleus lacking •Membrane-enclosed cytoplasmic organelles lacking •Cytoskeleton lacking-support from rigid cell wall Structure of a Eukaryotic Plant Cell Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Lecture Themes •origins, evolution and diversity •structure and function •ecological function and relationships Chapter 26: Bacteria and Archaea: the Prokaryotic Domains 1. Prokaryote Phylogeny Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Genome of the Archaeon Methanococcus jannaschii was sequenced in 1996. Sequencing of M. jannashcii confirmed Carl Woese’s longstanding hypothesis that life traces back to three main lineages, one of which (Archaea) includes prokaryotes that share a more recent common ancestry with eukaryotes than with the prokaryotic “true bacteria” Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Prokaryotic Structure and Function Chapter 26: Bacteria and Archaea: the Prokaryotic Domains (Keaton 1993) Cyanobacteria 10 um dia. E. coli 1X2 um Mycoplasma 0.3-0.8 um dia. Bacteriophage 0.07X 0.2 um Viroid 0.01 X 0.3 um Lymphocycte 10 um dia. Largest known prokaryote is the marine bacterium Thiomargarita namibiensis; bright white cell in upper left, about .75 mm dia., attached to two dead ones. Fruitfly in picture for size comparison. Paramecium 30X 75 um Sizes of viruses, bacteria and eukaryotes compared Most bacteria are 1-5 um diameter (most Eukaryotic cells are 10-100 um) Bacillus on the head of a pin Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Raven et al 2002 Spherical coccus (Enterococcus) Pseudomonas aeruginosa Streptococcus Spirillum volutans Bacterial Form Rod-shaped bacillus (E. coli) Three shapes are especially common among bacteria – spheres, rods and spirals Most are unicellular, some aggregate transiently, some form permanent aggregations of identical cells;some show division of labor between two or more specialized cell times Helical spirilla (|Aquaspirillum spirosa) Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Scanning electron micrograph of a colony of streptomyces, one of the actinomycetes. The actinomycetes have a much more complicated morphology than most other bacteria. (Keaton and Gould 1993) Chapter 26: Bacteria and Archaea: the Prokaryotic Domains •Most bacterial cell walls contain peptidoglycan (lacking in Archaea) •Gram staining is an important technique for identifying bacterial; cells stain differentially based on structure and composition of walls •Pathogenesis is related to cell wall structure and composition •Many antibiotics act by preventing formation of cell walls, by inhibiting synthesis of cross-links in peptidoglycan •Many prokaryotes produce capsules that function in adherance and protection Penicillium chrysogenum Neisseria gonorrhoeae •Many prokaryotes have surface appendages called pili that are function in adherance E. coli The exterior surfaces of Prokaryotes. Almost all prokaryotes have a cell wall, and in most that wall contains peptidoglycan – polymers of modified sugars that are crosslinked by short polypeptides Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Aquaspirillum sinosum Mechanisms of Motility Many bacteria are motile. Fllagellar action is the most common,but not the only mechanism, for generating movement. Spirillum volutans Borrelia burgdorferi •Prokaryotic flagella •Flagella-like helical filaments •Growing gelatinous threads Motility Behavior Lyme disease symptoms, and the disease vector – a tick •Kinesis •Taxis Chapter 26: Bacteria and Archaea: the Prokaryotic Domains 0.05 um 1 um Electron micrograph of E. coli shoing long helical flagella. Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Vibrio cholerae (pathogen responsbible for cholera); the unsheathed core visible at top of photo is composed of a single crystal of the protein flagellin. In intact flagella, core is surrounded by a flexible sheath. Rotary motion of the motor creates a kind of rotary motion when organism swims. Bacteria swim by rotating their flagella. Chapter 26: Bacteria and Archaea: the Prokaryotic Domains mesosome •various specialized membranes, but lacking extensive compartmentalization by internal membranes plasma membrane DNA The mesosome is an infolding of the plasma membrane serves as a point of attachment for DNA in some bacterial cells Infoldings of plasma membrane, similar in ways to cristae of mitochondria, function in cellular respiration in aerobic bacteria •ribosomes present but differ from eukaryotic ones in size and composition Exensive folded photosynthetic membranes are visisble in Prochloron cell. The single, circular DNA molecule is located in the clear area in the central region of the cell. •genomes are smaller and simpler than in eukaryotes; one major chromosome and, in some species, plasmids •Processes of DNA replicatin and protein translation are generally similar to eukaryotes Thylakoid membranes of photosynthetic cyanobacteria Cellular and Genomic Organization The organization of cellular components, including the genome, differs substantially between prokaryotes and eukaryotes Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Cell division Asexual reproduction by cell division via binary fission Mechanisms of gene transfer -transformation; genes from environment -conjugation; genes from another prokaryote -transduction genes via a virus Adaptation short generation time allows favorable mutations and novel genomes arising from gene transfer to spread quickly in rapidly reprducing Growth virtual geometric growth while in environments with unlimited resources Prokaryote Reproduction and Population Growth Prokaryote populations grow and adapt rapidly, through asexual reproduction as well as mechanisms involving gene transfer Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Dormancy and Endosporulation Some bacteria form highly resistant spores under harsh environmental conditions Sporulating Bacillus cell Antibiotic synthesis Some prokaryotes (and protists and fungi) synthesize and release antibiotic chemicals that inhibit growth of other microbes Bacillus anthracus Adaptations to Harsh Environmental Conditions: Some bacteria are capable of dormancy, endosporulation and antibiotic synthesis Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Nutritional and Metabolic Diversity Sources: Campbell et al (2002), Freeman (2002), Purves et al (2001) Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Nutrition; how an organism obtains two resources from the environment; -energy -carbon source to build the organic molecules of cells •Phototrophs; use light energy •Chemotrophs; obtain energy from chemicals taken from the environment •Autotroph; needs only the inorganic compound CO2 as a carbon source Hetertroph: requires at least one organic nutrient for making other organic compounds Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Sources: Freeman 2002, Campbell 2002 The basic themes of metabolism, among all domains are -extracting usable energy from reduced compounds -using light to produce high-energy electrons -fixing carbon. All organisms have mechanisms for trapping usable energy in ATP; ATP allows cells to do work; there is no life without ATP At one point or another, you have studied these metabolic themes as they occur Eukaryotes and perhaps Prokaryotes; photosynthesis(eg,in green plants and respiration (eg in all Eukaryotes) Prokaryotes show tremendous diversity in metabolic process.in that they have evolved dozens of variations on these most basic themes of metabolism This Prokarotic metabolic diversity is important for two reasons: 1.It explains their ecological diversity; they are found almost everywhere because they exploit such a tremendous variety of molecules as food 2.Global nutrient cycling of (eg nitrogen, phosphorous, sulfur, carbon) is mediated by, exists because, prokaryotes can use them in almost any molecular form Overview of photosynthesis and respiration Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Sources: Freeman 2002, Campbell 2002 Overview of cellular respiration One (very important!!) example of metabolic pathways by which many species obtain energy for generating ATP by oxidizing reduced organic compounds Highly reduced molecule, glucose, serves as original electron donor (ie, molecule is oxidized) and highly oxidized molecule, oxygen, serves as final electron acceptor Overview of Photosynthesis Many prokaryotes generate ATP by employing electron donors and acceptors other than sugars and oxygen, and produce by-products other than water Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Source: Freeman (2002), Purves et al (2001) Some Electron Donors and Acceptors Used by Bacteria and Archaea Electron Donor Electron Acceptor Product Metabolic Strategy * H2 or organic compounds SO42- H 2S sulfate-reducers H2 CO2 CH4 methanogens CH4 O2 CO2 methanotrophs 2- S or H2S O2 SO4 organic compounds Fe3+ Fe2+ NH3 O2 organic compounds NO3 NO2- O2 NO2 - - sulfur bacteria iron-reducers nitrifiers N2O, NO or N2 denitrifiers (or nitrate reducers) NO3- nitrosifiers * This column gives the name biologists use to identify species that use a particular metabolic strategy nitrification: oxidation of ammonia to nitrite and nitrate ions denitrification: reduction of nitrogencontaining ions to form nitrogen gas and other products Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Source: Freeman (2002) •lateral gene transfer has taken place repeatedly through transformation and viral infection •in transfers among bactera and archaea the primary mechanism probably involves loops of mobile DNA (plasmids) •swapped genes tend to be those involved in energy and carbon metabolism (not information processing , eg DNA replication, transcription, protein synthesis) – interesting…as metabolic diversity is a hallmark of the Bacteria and Archaea!! Lateral Gene Transfer. Gray branches show diversification of the three domains. Red branches show movement of genes from species in one part of the tree to species in other parts Chapter 26: Bacteria and Archaea: the Prokaryotic Domains Nutritional Diversity among Chemoheterotrophs (most known Prokaryotes) •Saprobes; decomposers that absorb nutrients from dead organic matter •Parasites; absorb nutrients from body fluids of living hosts Relevance of Oxygen to Metabolism among Bacteria and Archaea •Obligate aerobes •Facultative anaerobes •Obligate anaerobes