Download Bacteria and Archaea Generaliza,ons Three Most Common Shapes

1/30/12 Bacteria and Archaea Chapter 27 Generaliza8ons •  Most prokaryotes are unicellular, although some species form colonies •  Most prokaryo8c cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryo8c cells Three Most Common Shapes 1 1/30/12 The Cell Wall •  Maintains cell shape, provides physical protec8on, and prevents the cell from burs8ng in a hypotonic environment –  Contain pep#doglycan, a network of sugar polymers cross-­‐
linked by polypep8des •  Archaea contain polysaccharides and proteins but lack pep8doglycan •  Gram stain: a method of classifica8on •  Gram-­‐nega#ve less pep8doglycan and an outer membrane that can be toxic, and they are more likely to be an8bio8c resistant •  Many an8bio8cs target pep8doglycan and damage bacterial cell walls Fig. 27-­‐3 Carbohydrate por#on of lipopolysaccharide Pep#doglycan Cell wall Cell wall layer Outer membrane Pep#doglycan layer Plasma membrane Plasma membrane Protein Protein Gram-­‐ posi#ve bacteria (a) Gram-­‐posi#ve: pep#doglycan traps crystal violet. Gram-­‐ nega#ve bacteria 20 µm (b) Gram-­‐nega#ve: crystal violet is easily rinsed away, revealing red dye. Other Characteris8cs Capsule: A polysaccharide or protein layer covers many prokaryotes Fimbrae: (also called a"achment pili), which allow them to s#ck to their substrate or other individuals in a colony 2 1/30/12 Mo8lity •  Most mo8le bacteria propel themselves by flagella that are structurally and func8onally different from eukaryo8c flagella •  In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain s8muli Internal Organiza8on •  Prokaryo8c cells usually lack complex compartmentaliza8on •  Some prokaryotes do have specialized membranes that perform metabolic func8ons •  The prokaryo8c genome has less DNA than the eukaryo8c genome •  Most of the genome consists of a circular chromosome •  The typical prokaryo8c genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region •  Some species of bacteria also have smaller rings of DNA called plasmids Other Membranes 3 1/30/12 Reproduc8on and Adapta8on •  Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours •  Evolve rapidly because of their short genera8on 8mes •  Many prokaryotes form metabolically inac8ve endospores, which can remain viable in harsh condi8ons for centuries Gene8c Diversity •  Prokaryotes have considerable gene8c varia8on •  Three factors contribute to this gene8c diversity: –  Rapid reproduc8on –  Muta8on –  Gene8c recombina8on Rapid Reproduc8on •  Prokaryotes reproduce by binary fission, and offspring cells are generally iden8cal •  Muta8on rates during binary fission are low, but because of rapid reproduc8on, muta8ons can accumulate rapidly in a popula8on •  High diversity from muta8ons allows for rapid evolu8on 4 1/30/12 Gene8c Recombina8on I Transforma#on •  take up and incorporate foreign DNA from the surrounding environment Transduc#on •  movement of genes between bacteria by bacteriophages (viruses that infect bacteria) Conjuga#on •  Process where gene8c material is transferred between bacterial cells •  Sex pili allow cells to connect and pull together for DNA transfer •  A piece of DNA called the F factor is required for the produc8on of sex pili The F Factor As a plasmid •  Cells containing the F plasmid func8on as DNA donors during conjuga8on •  Cells without the F factor func8on as DNA recipients during conjuga8on •  The F factor is transferable during conjuga8on In the Chromosome •  A cell with the F factor built into its chromosomes func8ons as a donor during conjuga8on •  The recipient becomes a recombinant bacterium, with DNA from two different cells •  It is assumed that horizontal gene transfer is also important in archaea 5 1/30/12 The F Factor As a Plasmid In the Chromosome R Plasmid •  R plasmids carry genes for an8bio8c resistance •  An8bio8cs select for bacteria with genes that are resistant to the an8bio8cs •  An8bio8c resistant strains of bacteria are becoming more common Table 27-­‐1 6 1/30/12 The Role of Oxygen •  Prokaryo8c metabolism varies with respect to O2: –  Obligate aerobes require O2 for cellular respira8on –  Obligate anaerobes are poisoned by O2 and use fermenta8on or anaerobic respira#on –  Faculta#ve anaerobes can survive with or without O2 Role in Chemical Cyclinng •  Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems •  Chemoheterotrophic prokaryotes func8on as decomposers, breaking down corpses, dead vegeta8on, and waste products •  Nitrogen-­‐fixing prokaryotes add usable nitrogen to the environment •  Prokaryotes can some8mes increase the availability of nitrogen, phosphorus, and potassium for plant growth •  Prokaryotes can also “immobilize” or decrease the availability of nutrients Symbio8c Rela8onships •  Symbiosis is an ecological rela8onship in which two species live in close contact: a larger host and smaller symbiont •  Prokaryotes oden form symbio8c rela8onships with larger organisms •  In mutualism, both symbio8c organisms benefit •  In commensalism, one organism benefits while neither harming nor helping the other in any significant way •  In parasi#sm, an organism called a parasite harms but does not kill its host •  Parasites that cause disease are called pathogens 7 1/30/12 Human Pathogens •  Prokaryotes cause about half of all human diseases •  Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins •  Exotoxins cause disease even if the prokaryotes that produce them are not present •  Endotoxins are released only when bacteria die and their cell walls break down •  Many pathogenic bacteria are poten8al weapons of bioterrorism Benefits of Prokaryotes •  Experiments using prokaryotes have led to important advances in DNA technology •  Prokaryotes are the principal agents in bioremedia#on, the use of organisms to remove pollutants from the environment •  Some other uses of prokaryotes: –  Recovery of metals from ores –  Synthesis of vitamins –  Produc8on of an8bio8cs, hormones, and other products You Should Now Be Able To: 1.  Dis8nguish between the cell walls of gram-­‐posi8ve and gram-­‐nega8ve bacteria 2.  State the func8on of the following features: capsule, fimbriae, sex pilus, nucleoid, plasmid, and endospore 3.  Explain how R plasmids confer an8bio8c resistance on bacteria 4.  Dis8nguish among the following sets of terms: photoautotrophs, chemoautotrophs, photoheterotrophs, and chemoheterotrophs; obligate aerobe, faculta8ve anaerobe, and obligate anaerobe; mutualism, commensalism, and parasi8sm; exotoxins and endotoxins 8