Chapter 19 Peptidoglycan:cross-linked polymer of amino sugars that produces mesh-like structure around cell◦ unique to bacteria(seperates archaea and bacteria) Gram positive bacteria=blue-purple◦ thick peptidoglycan layer Gram negative bacteria=pink-red◦ thin peptidoglycan wall Bacteria shapes:coccus(spherical),bacillus(rod),spirillus(spiral) Low GC Gram-pos.◦ Low (less than 50%) G-C to A-T nucleotide pairs in DNA ◦ Produce endospores(heat-resistant resting structures) High G-C Gram pos.◦ higher ratio of G-C to A-T nucleotide pairs◦ reproduce by forming chains of spores of tips of filaments◦ most antibiotics come from high G-C gram pos. Hyperthermophilic bacteria◦ extremophiles, used to be thermophiles Hadobacteria◦ thermophilic extremophiles Cyanobacteria◦ Blue-green bacteria because of pigmentation◦ phtosynthetic bacteria◦ can differentiate into three types: ▪ vegetative cells: photosynthesize▪ spores:resting stages that survive harsh environments and develop into filaments▪ Heterocysts: fix nitrogen Spirochetes◦ Gram-neg motile bacteria◦ characterized by axial filaments(modified flagella )◦ Cell body=long cylinder coiled into helix Chlamydias◦ only parasites ◦ gram negative◦ can take ATP from hosts◦ life cycle involves two different forms of cells:elementary and reticulate bodies Proteobacteria◦ Some N-fixers◦ largest group of bacteria◦ many gram neg. photoautotrophs  Archaea◦ two groups:crenarchaeota and Euryarchaeota◦ absence of peptidoglycan and presence of distinctive composition in cell membranes◦ many extremophiles Many microbial communities tend to form dense biofilms ◦ biofilms:sticky, gel-like polysaccharide matrix that traps other cells  Obligate anaerobes:oxygen sensitive organisms Facultative anaerobes:prokaryotes that can shift between anaerobic and aerobic modes Aerotolerant anaerobes:can't conduct cellular respiration, but not damaged by oxygen whenpresent Obligate aerobes:unable to survive in absence of oxygen Photoautotrophs:perform photosynthesis Photoheterotrophs:use light as energy source but must obtain carbon atoms from organic compounds made by other organisms Chemolithotrophs:energy obtained by oxidizing inorganic substances, and use some energy to fix carbon Chemoheterotrophs:energy and carbon atoms from one or more complex organic compounds that have been synthesized by organisms Denitrifiers:give back nitrogen gas to atmosphere Nitrifiers:convert nitrogen so plants can use Bacteria evolve through lateral gene transfer and gene