Bacteria are the most ancient life forms - signs from ~3,500 m.y.a. Bacteria can tolerate great physical extremes from ocean deeps to the stratosphere to inside rocks & earth's crust essentials = only H20 + energy + matter vast metabolic diversity, mostly unique; unique - sources of energy & matter 1 mostly extremely tiny - 0.1-10 x 10-6 m. but extremely numerous: 1 spoon garden soil - 1010 cells 1 cm2 gum scrape - 109 cells 2 l metabolic activities exchange all major reactive gases with atmosphere : N2, N2O, O2, CO2, CO, H2, CH4, NH3, H2S and others total weight of all earth's = 1/10 all earth's mammals also central in cycling C, P, S cover all surfaces, interior & exterior; mainly benign or beneficial open genetic exchange; sex reproduction 3 several of these re-cyclings are restricted to - notably N2 photosynthetic began the change in character of earth's atmosphere ~3 b.y.a. most are morphologically simple - single cells 4 some generate temporary multicellular structures some form colonies 5 6 1
Prokaryote vs. vs. Eukaryote structure Prokaryotes vs. Eukaryotes 1-10 x 10-6m 10-100 x 10-6m nucleoid, genophore nucleus, chromosomes no organelles mitochondria, Golgi, E.R. simple flagellum tubulin cilia highly diverse metabolism 7 uniform metabolism mostly aerobic 8 stromatolites ~2 x 109 year l dominance oldest stromatolites oldest rocks 3.9 Ar Pr structures from l mats plus mineral particles oldest eukaryotes Ha 4.5 b.y.a. fossil Phanerozoic 9 now recognised that this is poor indication of true historical-genealogical relationships Cyano true relationships becoming revealed by small-subunit ribosomal RNA (16S rrna) sequences 11 10 16S rrna shows two major groups BACTERIA & ARCHAEA (= Eu & Archae) traditionally, have been classified according to shape, chemistry & metabolism such similarities are mostly convergent living tend to live in extreme environments hot, acidic, salty, anoxic 12 2
live in environments typical of very early earth: Halophils extremely hot (up up to ~300 C), ~300 C acidic and osmotically challenging conditions Cyano hot springs; super-hot deep-sea vents hypersaline seashores - 3-5 Molar NaCl anoxic muds and soils, sewage, guts 13 in early earth environment, physical processes (lightning, heat, UV) generated stew of organic molecules, rich in energy anaerobic fermentation thought probably the earliest global metabolism as life grew, organic supplies dwindled... strong selection for autotrophic capability: energy and C from inorganic inorganic sources this is exactly what methanogens can do 15 Thermacidophils 14 (O2 intolerant) Cyano reduce C with H2 -> CH4 C from CO2, formate, formate, methanol & acetate H from H2, formate, methanol & acetate [CO2] + 4H2 -> CH4 + 2H2O prevent accumulation of C in sediments by releasing it back to atmosphere 2O2 + CH4 -> CO2 + 2H2O thus prevent accumulation of O2 in air 16 eventually, use of sunlight energy evolved PHOTO-AUTOTROPHY we think of photosynthesis as generating O2 NEXT CLASS but first forms, probably still O2-intolerant, -intolerant used H2, H2S etc. as reducing agents for CO2 Other forms of autotrophic activity: changing the world s atmosphere 2H2X + CO2 -> CH2O + 2X X + H2O use of water + sunlight a stunning technique 17 massive consequences for earth's atmosphere and its life... 18 3
100 oxygenic photosynthesis developed ~2.5 b.y.a. (end-n) O2 accumulated, accumulated raising level from 0.01% of atmosphere then to 20% today (~10% ~10% at ~0.5 b.y.a. - first vertebrates) 50 % today's O2 10 5 first O2 photosynthesizers were probably just like today's Cyano dominated 2.5-0.6 b.y.a. - stromatolites global primary production LOG SCALES 2 3 19 Cyano 0.1 1.0 0.4 billions of years ago 20 OXYGEN AS A PROBLEM highly reactive; oxidises organics to CO2 O2-, OH-, H2O2 seriously disruptive O2 -> O3, which screens UV; this further reduces production of organics O2 production was a serious problem for O2-intolerant forms Cyano they had to retreat to O2-free places or evolve tolerance 21 selection for new metabolic styles and ways of dealing with free O2 catalases, peroxidases to convert free radicals USE O2 to oxidise organics - respiration fermenting - 1:18 1:18 - respiring 22 24 one way of dealing w/free radicals involves luciferin; light emitted with reaction this is bioluminescence most biotic light production involves symbiosis with bioluminescent 23 4
Bacterial Metabolic Diversity huge diversity, even within "species can switch according to conditions found in addition to eukaryote processes: aerobic respiration and O 2 photosynthesis and ethanol & lactate fermentation (organoheterotrophy & photoautotrophy) chem. energy org. carbon light energy inorg. carbon (CO 2 ) non-o 2 photoautotrophy - H 2 S, H 2 lithoautotrophy - methanogenesis, N 2 -fixation lithoheterotrophy heterotrophy - metal oxidizers 25 thus perform a bewildering diverse array of metabolic activities most are different from those of eukaryotes for most l metabolic by-products, there are other who can use them as substrates for their own activities entirely self-contained l communities can be independent of eukaryotes 26 we shall sample l activities through looking at how they contribute to the cycling of life's essential elements crucial in cycling of N 2, S and metals major contributions to C, P cycling substantial impact on O 2 balance 27 Nitrogen Cycle Rhizobium nodules Nitrogen-fixers can be free or symbiotic, aerobic or anaerobic, lithotrophic, organotrophic or phototrophic fermenting and respiring decomposer Nitrifying are unique in fixing N 2 gas 28 Cyano assimilation SO 2-4 Sulphur Cycle organic sulphur (and fungi) decomposition H 2 S heavy metal cycling Iron-Oxidizing (lithoautotroph) photosynthetic oxidation S and green S- 29 several groups oxidize Fe 2+ to Fe 3+ usually under acidic conditions 30 5
Cyano CO2 Carbon Cycle Terrestrial generally live in H2O films on soil particles photosynthesis densest and most diverse communities live near surface - most organic debris major contributions to cycling of C, N & O decomposition CO2 methanogens guts etc. 31 Aquatic Marine generally poorly represented except at shores and in great deeps aphotic hydrothermal vents vents produce 270-380 C water w/highconcentrations of H2S, H2, CO, Mn2+ Bacterial Ecology respiration lithotrophic provide base of special communities, independent of sun 33 live on all biological surfaces; occasionally pathogenic 32 Aquatic Freshwater Most primary production is done by and algae dominate in anoxic, extreme parts much primary production is respired by the, consuming O2 excess organics -> O2 depletion dynamics of both C and O closely linked through l activities 34 cyano s Treponema - syphilis PLANTS spirochaete Neisseria - gonorrhea, meningitis cilia ANIMALS fermenting archaebacterium Borellia - Lyme disease mitochondria FUNGI Vibrio - cholera 35 respiring bacterium 36 6
This SET view now broadly accepted but long-resisted; symbiosis now recognised as being very common in life Other symbioses lichens corals vent-worm root nodules mycorrhizae 37 NEXT CLASS: The Protoctista - the simplest Eukaryote organisms 38 thanks to the authors of the following sites http://www.bact.wisc.edu/bact303/bact303mainpage http://www.bact.wisc.edu/bact303/majorgroupsofprokaryotes http://lifesci.ucsb.edu/~biolum/organism/photo.html 39 7