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~1.7 billion years of prokaryote dominance Summer Bio153S Lecture 7: prokaryotes earliest eukaryotes (1.8 b.y.a.) Archaean 1400 m.y. oldest stromatolites (3.5 b.y.a.) oldest rocks Hadean 1900 m.y. Proterozoic 600 m.y. Paleozoic era Mesozoic era Cenozoic era origin of earth (4.5 b.y.a.) Phanerozoic prokaryote cell structure is simple • • • • • • • no cytoskeleton no membrane-bound organelles binary fission; no mitosis DNA in nucleoid (not nucleus) no chromosomes permanently haploid flagellum is simple distinctive cell walls: most are single cells but some form colonies 1 may form temporary multicellular forms - no complex cell junctions • conjugation: plasmid or chromosomal DNA transferred through pilus genetic recombination separate from reproduction prokaryotes are everywhere • resting spores of Bacillus permians (last active 250 million years ago) was “resurrected” in 2000! • 1 gram of soil has > 10,000 bacterial types • divide rapidly: under ideal conditions E. coli could produce mass > earth in 3 d! • 30 km above Earth’s surface; < 2 km deep in crust eukaryotes are metabolically conservative 1) most are organoheterotrophs (carbon + energy from macromolecules) prokaryotes are metabolically diverse carbon + energy 1.inorganic (autotrophs) 2.organic (heterotrophs) 1. sunlight (photo) 2. chemicals (chemo) i. organic (organo) ii. inorganic (litho) prokaryotes: 1) photoautotrophs 2) photoheterotrophs 3) chemoautotrophs 2) plants and some protists are photoautotrophs (carbon from CO2; energy from sunlight) 4) chemoheterotrophs important in nutrient cycling 2 prokaryotes vary in mode of respiration 5 major groups in Eubacteria: aerobic: O2 is electron receiver anaerobic: NO3-, SO42-… proteobacteria • most diverse group • mostly Gram -ve • E. coli • important in N2 fixation • “purple bacteria” nitrogen fixation purple bacteria • use energy from the sun but extract electrons from substances other than water • photosynthesis does not release oxygen • most species are strict anaerobes some proteobacteria are human pathogens • e.g. Rhizobium: symbiosis with legumes Helicobacter pylori • makes nitrogen bioavailable ulcers Yersinia pestis bubonic plague Salmonella food poisoning 3 spirochetes • Gram-negative bacteria • difficult to culture • long, thin, helical and motile • axial filaments • Treponema - syphilis • Borellia – Lyme disease firmicutes • mostly Gram +ve • e.g. Streptomyces: source of antibiotics (Streptomycin, Neomycin and Chloramphenicol) • some form endospores (tetanus) chlamydias • obligate intracellular parasites • extremely tiny • human pathogen: STD’s, trachoma cyanobacteria • aquatic and photosynthetic • contain chlorophyll a • photosynthetic lamellae (thylakoids) called “blue-green algae” • The Red Sea: occasional blooms of Oscillatoria • flamingos: pink from eating Spirulina stromatolites • reef-like structures • cyanobacteria and other prokaryotes in mineral matrix • mucilaginous mats of bacteria! 4 • range from the Early Archean (3.5 BYA) to recent • thrive in hypersaline water early cyanobacteria changed the atmosphere • chemically splitting water: 2 H2O ⇒ 4 H+ + O2 + 4e• electrons reduced CO2 to form organic compounds • released O2 into atmosphere prokaryotes: • can exploit many env’ts • many substrates and end-products • can form self-contained communities • reactions with atmospheric gases allowed for evolution of eukaryotes 5