Chapter 27 Bacteria and Achaea Many prokaryotes can survive extreme conditions o Halobacteria most salt tolerant species on earth Use red pigment to capture sun energy Use K pumps to compensate for water loss Natural selection causes their extreme diversity Unicellular some might stay attached after division Diameter of 0 5 5 micrometers Well organized all life functions in 1 cell 3 main shapes o Coccus spherical o Bacillus rod Structural and Functional Adaptations contribute to Prokaryotic Success o Spirilla and spirochetes spiral Cell surface structures o Cell wall maintains shape and prevents bursting due to the hypotonic environment in which they live Will shrivel and plasmolyze in a hypertonic solution which is why salt is such a good bacterial prevention o Cell wall made of peptidoglycan polymer of modified sugars cross linked by short peptides Archaeal cell walls have polysaccharides and proteins but no peptidoglycan o Gram staining allows us to classify bacteria into 2 groups 1st stained with crystal violet and iodine rinsed with alcohol and then stained again with safarin o Structure of wall determines response Gram positive Simple walls with more peptidoglycan Gram negative Less peptidoglycan and have an outer membrane lipopolysaccharides lipids bonded to carbohydrates o Knowledge of gram response important for treatment of bacterial infections Outer membrane of gram negative bacteria Lipids in the outer membrane of gram negative bacteria are often toxic Protects from drying out Resistant to antibiotics Penicillin inhibits peptidoglycan formation destroys gram positive cells o Capsule slime layer sticky layer of polysaccharides proteins around the cell wall of many prokaryotes Protects against dehydration the immune system o Fimbriae hair like appendages used to stick together Shorter and more numerous o Pili appendages that pull cells together for DNA transfer aka sex pili Motility o Taxis directed movement toward away from a stimulus Chemotaxi change in movement because of chemicals o Flagella structure used to move Either scattered across bacterium or clustered at ends Structural and molecular comparisons suggest analogy of bacterial archaeal and eukaryotic flagella 3 main parts motor hook and filament Modified slowly over time Flagella are an exaptation from existing secretory genes Internal organization and DNA o Circular chromosome with fewer associated proteins o Nucleoid area of DNA concentration o Plasmid ring of independently replicating DNA o Ribosomes slightly different allows some antibiotics to target bacteria Reproduction and adaptation o Can reproduce quickly by binary fission o Reproduction is limited by nutrient supply metabolic wastes that might kill the bacteria competition or consumption o 3 key features Small Reproduce by binary fission Short generation times Allows for fast evolution Prokaryotes o Endospore resistant cells developed when lacking an essential nutrient Cell copies chromosome and surrounds it with tough multilayered structure Water is removed and metabolism stops Original cell lyses and endospore remains Can survive heat desiccation and pressure for centuries then rehydrate and resume metabolism Rapid Reproduction Mutation and Genetic Recombination Promote Genetic Diversity in Although binary fission makes clones mutations can still occur o These are amplified by the short generation times and large population sizes causing fast evolution Genetic recombination is achieved by horizontal gene transfer o Horizontal gene transfer movement of genes from one species to another o Transformation genotype and phenotype altered by uptake of foreign DNA from surroundings Recombinant contains DNA from 2 different cells in chromosome Many bacteria have cell surface proteins that recognize and transport DNA into the cell o Transduction phages carry prokaryotic genes from 1 cell to another Accidents during phage reproduction phage cannot reproduce itself but may still inject prokaryotic DNA into another cell o Conjugation DNA transferred between 2 prokaryotic cells usually the same species One way transfer one cell donates DNA the other receives it Pilus attaches to recipient and pulls it in A mating bridge forms and DNA passes through F factor fertility factor DNA piece that codes for the ability to form a pilus and donate DNA for conjugation 25 genes mostly for the pilus F plasmid F cells are the donors can convert F to F if the F plasmid is transferred F factor in chromosome o Chromosomal genes transferred if the F factor is in the DNA sequence o Hfr Cell high frequency of recombination cell with F factor in the chromosome o Segments of transferred DNA might align and exchange making a recombinant bacterium R plasmid plasmids that confer resistance to antibiotics Might alter target protein or destroy hinder antibiotics Can carry resistance to several antibiotics Diverse nutritional and Metabolic Adaptations Have Evolved in Prokaryotes Variations among prokaryotes shown in diverse nutritional adaptations Autotrophs make their own organic compounds o Phototrophs use light to make food o Chemotrophs food from chemicals Heterotrophs require at least 1 organic nutrient o Obligate aerobes must have oxygen o Obligate anaerobes cannot have oxygen Exclusively fermentation or anaerobic respiration using some other compound as the final electron acceptor o Facultative anaerobes can respire anaerobically or aerobically Nitrogen fixation o Heterocysts Specialized Cyanobacteria that fix nitrogen NH3 from atmospheric into nitrate Biofilm large colonies of specialized prokaryotic cells that stick together and have channels for nutrients Partnership between sulfate consuming bacteria and methane consuming aracheae in balls on the ocean floor eat up methane Molecular Systematics is Illuminating Prokaryotic Phylogeny In the past prokaryotic taxonomy was based on shape mobility nutrition and gram staining o Still useful medically but doesn t show evolutionary history Molecular systematics o Found Achaea more closely related to eukarya o Many groups have similar characteristics o DNA analysis originally limited to those prokaryotes that could be cultured but PCR can now be run on samples from the field o Horizontal gene transfer between prokaryotes makes it hard to make a tree It is clear that Achaea and bacteria come from 2 separate lineages Achaea o Extremophiles survive extreme environments Extreme halophiles can survive and sometimes require highly saline
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