Bacteria and Archaea Chapter 26

TREE OF LIFE 26.1 The tree of life has 3 Domains (superkingdoms): Eukarya Bacteria Archae Prokaryotes: simple cells that lack a nucleus and lack membrane-bound organelles; All bacteria; in Domains Bacteria and Archae

BACTERIAL CELL Bacteria were first living organisms on Earth; appeared about 3.5 bya; 1 billion years after Earth was formed Prokaryotes Asexual/binary fission 1 circular chromosome in nucleoid region Plasmid: small circularl non- necessary DNA Peptidoglycan cell wall Penicillins kill this way Gram stain: distinguishes by cell wall differences

GRAM STAINING Gram+: stains blue/purple; very simple but thick peptidoglycan cell walls (picks up stain) Gram -: stains pink: complex cell walls but thinner; much less peptidoglycan; more often pathogenic (disease causing)

PROKARYOTIC SHAPES/SIZES Bacterial cells are very small (200 nm – 2 micrometers); must be small to obtain nutrients by diffusion Shapes: Spheres: coccus Rods: bacillus Sprilas or filaments: spirella or spirochetes

MYXOBACTERIUM Some bacteria like to clump, or aggregate

Bacterial genome: small, chromosome 100% DNA, lack introns Obtain new genes: horizontal gene transfer most worrisome problem: rapid spread of antibiotic resistance 3 Types of Horizonal Gene Transfer:  Conjugation  Transformation  Transduction (by viruses) HORIZONTAL GENE TRANSFER

CONJUGATION Also called “gene swapping”; transfers plasmids from one cell to another through sex pili Allows the sharing of genes such as antibiotic resistance (R plasmid)

TRANSFORMATION Gene transfer with no bridge between them Dead donor cell releases DNA into environment and taken up by recipient

TRANSDUCTION Virus (called bacteriophages) transfers DNA from a donor to a recipient cell; takes donor/host DNA and incorporates it into viral DNA

 In eukaryotes, sexual reproduction is the main way by which new gene combinations are generated. How do bacteria generate new gene combinations in the absence of sexual reproduction? QUICK CHECK

 In prokaryotes, genes are transferred from one organism to another by horizontal gene transfer…..facilitating the generation of new gene combinations.  Conjugation  Transformation  Transduction ANSWER

THIRD DOMAIN For years, all prokaryotes were classified as Bacteria. This changed in 1977 from research looking at RNA pieces of ribosomes. Archea: 2 nd prokaryotic domain No nucleus and no membrane-bound organelles Cell size & physical characteristics same Differences: Diff lipids in membranes No photosynthesis with chlorophyll Have histone proteins Capable of methanogenesis Not sensitive to antibiotics No peptidoglycan in cell walls

CHARACTERISTICS OF ARCHAEA

ARCHAEON ENVIRONMENTS Archeons have: Unusual physiological properties Transcription similar to Eukarya Translation differences Inhabit harsh environments/extremophiles Very hot Very salty Low pH Recently found in soil, lakes, oceans

MICROBIAL MATS 26.2 Bacteria and Archae are notable for their metabolic diversity. Bacteria are capable of oxygenic PS (using water as electron donor and producing oxygen as byproduct) Also of anoxygenic PS ( using electron donors other than water, such as H 2 S, H 2, and Fe 2 +)

LAYERS OF MICROBIAL MATS

BACTERIOCHLOROPHYLL Anoxygenic PS bacteria absorb sunlight using bacteriochlorophyll; these bacteria do not release oxygen as a byproduct

RESPIRATION WITHOUT OXYGEN Prokaryotes are required to sustain Earth’s carbon cycle; eukaryotes are optional for that purpose.

 Energy  Sunlight: phototrophs  Chemical compounds: chemotrophs  Carbon  Inorganic molecules, CO 2 : autotrophs  Organic molecules, glucose: heterotrophs  Photoautotrophs (plants, algae, cyanobacteria)…….photosynthesis; give off O2; rare in bacteria  Chemoheterotrophs (animals, fungi, many prokaryotes). Most bacteria.  2 subgroups  Saprobes: decomposers that absorb nutrients from dead organic matter  Parasites: absorb nutrients from body fluids of living hosts  Photoheterotrophs (rare microorganisms)  Chemoautotrophs (rare microorganisms) ACQUIRING ENERGY AND CARBON

HYDROTHERMAL VENTS Chemoautotrophs fuel the carbon cycle in deep-sea hydrothermal vents

SULFUR CYCLE 26.3 In addition to their key roles in the carbon cycle, Bacteria and Archae are critical to the biological cycling of sulfur and nitrogen. Human bodies are made up of 0.2% S Where do we get it? From the food we eat; from the food they eat Plants take in S from soil by assimilation. After cell death, fungi and bacteria decompose cells, returning S to environment; the reduced S compounds are then oxidized by bacteria and archeons…..completing the oxidation-reduction reactions that are linked to the carbon cycle.

NITROGEN CYCLE Nitrogen is present at 4% in human body Air is 79% nitrogen gas (N 2 ), but cannot be used by primary producers. Nitrogen fixation: The process by which bacteria and archeons can reduce nitrogen gas to its useable form….ammonia (NH 3 ). The N cycle also involves oxidation/reduction reactions that are linked to the carbon cycle.

EXAMPLE OF NITROGEN FIXATION Soybean roots have nodules that harbor nitrogen-fixing bacteria. Mutually beneficial relationship between soybeans and nitrogen-fixing bacteria

BACTERIAL DIVERSITY IN OCEANS Genomic 26.4 The extent of bacterial diversity was recognized only when sequencing technologies could be applied to non- culturable bacteria. The oceans are full of bacteria. Bacterial diversity in oceans is huge and still largely unexplored.

PROKARYOTIC PHYLOGENY Some scientists argue that evolution of prokaryotes should be viewed as a series of branches (web/bush) that diverge and then come together as new organisms because of horizontal gene transfer.

PHYLOGENY OF WHOLE GENOMES Proteobacteria: Most diverse group Involved in the biogeochemical and carbon cycles Gram + Bacteria: Thick peptidoglycan cell wall Strep, Staph Principal sources of antibiotics Cyanobacteria (photoautotrophs): Oxygenic photosynthesis

CYANOBACTERIA Found in a range of environments Deserts to open ocean Spherical, unicellular rods, multicellular balls and filaments

PHYLOGENY OF ARCHAEA 26.5 The diversity of Archae has only recently been recognized. Live in very different environments than Bacteria Where energy for growth is not available Extreme heat, high acidity, high salt Diverged from common ancestor 3 bya Has 3 major divisions 1. acid loving 2. methane producing 3. salt loving

ACID-LOVING ARCHAEONS A number of archeons grow in highly acidic waters, such as those associated with acid mine drainage.

ARCHAEONS IN THE OCEAN

FOSSIL RECORD OF BACTERIA 26.6 The earliest forms of life on Earth were Bacteria and Archae. Evidence for early Earth come from microfossils – called stromatolites – and isotopes of sedimentary rock

EARLY EARTH FROM BACTERIAL FOSSILS Life on Earth originated 3.5 bya with Bacteria and Archae Early atmosphere and oceans contained no free oxygen Oxygen began to accumulate about 2.5 bya due to cyanobacteria utilizing oxygenic photosynthesis

STROMATOLITES Stromatolites: layered structures that record sediment accumulation by microbial communities. Earliest records of life on Earth.

HUMAN MICROBIOME There are more than 750 bacterial species in our bodies Mouths Colon Skin Urogenital tracts Airways

MICROBIOTA We affect our gut bacteria by what we eat and the antibiotics we take.