Topic 9 Prokaryotes PDF

Topic 9 Prokaryotes Learning Outcomes • • • • • • • • Differentiate bacteria and archaea based on morphological and anatomical characteristics Classify specific structures into Gram (+) and Gram (-) bacteria Defend the importance of bacteria using quantitative or qualitative examples Classify org...

Topic 9 Prokaryotes Learning Outcomes • • • • • • • • Differentiate bacteria and archaea based on morphological and anatomical characteristics Classify specific structures into Gram (+) and Gram (-) bacteria Defend the importance of bacteria using quantitative or qualitative examples Classify organisms based on nutritional requirements Provide arguments for the importance of prokaryotes in the ecosystem Explain how cellular mechanisms in bacteria can influence populations dynamic and evolution Describe mechanisms that can lead to the evolution of antibiotic resistance Explain three processes that can lead to the formation of a recombinant bacteria 2 https://www.wooclap.com/BIO1130 3 Topic 9 Bacteria and archaea 9.1 – Characteristics of prokaryotes Prokaryotes Pro- (before in Greek) and karyon- (nucleus in Greek). The group of prokaryotes is considered a paraphyletic group à group of taxa that includes the common ancestor (L.U.C.A, likely a procaryote) and some of its descendants. 750,000 species Archaea are not bacteria! s ote y r ka o r P 5 Prokaryotes • 0.5-5µm in size. • Plasma membrane which constitutes a selective barrier with the environment. • Cytoplasm (content of the cell within the plasma membrane) is only made of the cytosol: internal fluid containing organic molecules, proteins, metabolic waste, etc. • Absence of nucleus: circular chromosome located in the nucleoid (region not enclosed by a membrane). • Fimbriae: short appendages helping bacteria to adhere to the substrate or to other cells. • Capsule: dense layer of polysaccharide or protein surrounding the cell wall. à protects the cell and allows the bacteria to adhere to substrates or cells • Absence of organelles (membrane-enclosed structures with specialized functions) 6 Prokaryotes • Bacteria lack histones (proteins that bind to the DNA and play a key role in the packaging of the genome in eukaryotic cells) but are present in some archaea. • Protective cell wall made of peptidoglycan in bacteria (very different in archaea, made of pseudomurein). • Flagellum: long cellular appendage specialized for locomotion à Taxis: directed movement towards or away from a stimulus 7 Gram classification • Bacteria can be classed according to the structure of their cell wall into Gram (+) and Gram (-) • Gram negative bacteria tend to be more resistant to antibiotic (the outer membrane blocks water soluble antibiotics) a iated by t n e r e f f i d hnique Can be c e t g n i ain Gram st Clostridium tetani (tetanus) Staphylococcus aureus (infections and food intoxications) Escherichia coli (gastroenteritis) Yersinia pestis (plague) 8 Topic 9 Bacteria and archaea 9.2 – Nutrition and growth Are bacteria good or bad? Bacteria 11 Nutritional requirements Abundance and diversity in the microbiome can vary between/within a host. Bacteria can be responsible for many infectious diseases 1012 human cells for 1013 bacteria! à Digestion, vitamins, immunity, protection against infections… Microbiome: community of microorganisms that live on and in the human body (up to 400 species in the gut). Commensalism: symbiotic relationship where an organism benefits but the other is not helped or harmed. 12 Nutritional requirements Organism Light Chemical compound Glucose, H2S, NH3 Phototroph Chemotroph Energy source Carbon source Inorganic compound (ex: CO2, HCO3-) Organic compound (Glucose) Inorganic compound (ex: CO2, HCO3-) Photoautotroph Photoheterotroph Chemoautotroph Anabaena sp. Rhodobacter sp. Sulfolobus sp. Organic compound (ex: Glucose, lipids) Chemoheterotroph Clostridium sp. 13 Nutritional requirements Organism Light Chemical compound Glucose, H2S, NH3 Phototroph Chemotroph Energy source Carbon source Inorganic compound (ex: CO2, HCO3-) Organic compound (Glucose) Inorganic compound (ex: CO2, HCO3-) Photoautotroph Photoheterotroph Chemoautotroph Anabaena sp. Rhodobacter sp. Sulfolobus sp. h Lithotrop roph Organot Organic compound (ex: Glucose, lipids) Chemoheterotroph Clostridium sp. 14 Role of prokaryotes in the ecosystem Food webs depend on primary producers (ex: photoautotrophs) for two things: 1. Absorbing energy from outside the ecosystem (ex: sunlight): à Photoautotroph (ex: cyanobacteria) can… • convert CO2 into sugars that enter the food chain • produce O2 used by chemoheterotroph during respiration • fix atmospheric N2 and produce proteins/nucleic acids Cyanobacteria 2. Assimilating minerals into biomass that is passed on upper trophic levels. à Decomposers: absorb and convert nutrients from nonliving organic material (corpses, fallen plant material…) into inorganic forms. = recycling of C, H, O, N, P between the biotic and the abiotic world. 15 Asexual reproduction Reproduction by binary fission: doubling in size and simple division in half (≠ mitosis) Binary fission requires the replication of the genome, initiated at the “Origin of Replication” The two daughter cells are clones of the mother cell. Escherichia coli 16 Asexual reproduction Reproduction by binary fission: doubling in size and simple division in half (≠ mitosis) Binary fission requires the replication of the genome, initiated at the “Origin of Replication” The two daughter cells are clones of the mother cell. The population doubles every generation à exponential growth curve (linear on a log scale) 1. Lag phase: synthesis of components required for growth 2. Log phase: rapid growth through cell divisions by a factor of 2n (n = number of generations) 3. Stationary phase: population stops to grow (lack of nutrients, oxygen, metabolic waste accumulation, etc.), activation of stress response 4. Death phase: exponential loss of viability due to lack of nutrients, oxygen or prolonged exposure to waste 17 Prokaryotes can evolve rapidly ll are sti s n o i t Popula and adapting g )! growin generations 00 (>75,0 Dr. Richard Lenski started a Long-Term Evolutionary Experiment (LTEE) in 1988 • 12 populations of E. coli are grown in parallel in low-glucose medium • All populations adapted over time and grew faster compared to the ancestral population (= the control population) • New mutations allowed populations to use glucose more efficiently (adaptation) • At generation ~33,000 one population started to use citrate as a carbon source à A mutation in the citT gene allowed the transport citrate inside the cell in the presence of O2 à Even rare mutations during DNA replication (1 per 10 million divisions) can lead to rapid adaptation (large populations and short generation time ~20min) à Despite their small size and small genome, bacteria can evolve rapidly to harsh conditions. They have evolved for 3.5 billion years and are still evolving! 18 Topic 9 Bacteria and archaea 9.3 – Antibiotic resistance and genetic recombination Resistance to antibiotics Antibiotic: molecule that kills or inhibits the growth of bacteria Bacteria can evolve resistance to antibiotics! • Mutations can alter genes coding for proteins that are the target of antibiotic à genetic variation between bacterial strains Normal bacteria colony Growth inhibition zone Penicillium colony (fungus) • Resistance can be transmitted vertically through inheritance à heritability of the acquired resistance • Only the resistant strains can grow à selection for resistance Penicillium inhibiting bacterial growth (Fleming 1929) Metabolism Cell wall DNA polymerase RNA polymerase But… more and more resistant strains à Many new antibiotics are synthesized to inhibit new cellular targets Cell membrane Protein synthesis 20 Conjugation Strains of bacteria from the same species can donate DNA through conjugation: 1. Two cells are temporarily joined through a pilus (hair-like structure) that draws the receiver cell closer 2. Establishment of a mating bridge (direct contact) 3. A plasmid (small circular chromosome) can be transferred from the donor to the receiver. F factor (Fertility factor) contains genes required to make the pilus (= selfish DNA: DNA that enhances its own transmission) Genes carried by the R plasmid confer antibiotic resistance and can also spread through conjugation. R plasmid: resistance plasmid which contains both the antibiotic resistance genes… and the genes coding for the sex pilus (just like the F-factor does). 21 Transduction Infection from a phage Bacteria can also exchange DNA through a virus called bacteriophage (a virus that infects bacteria). Replication of the phage genome and protein synthesis Assembly of the phage some bacterial DNA can be packaged in the new virus Infection of a new bacteria and recombination allows the integration of the donor’s allele in the recipient’s genome à The phage therefore represents an intermediate between a donor cell and a recipient cell. New bacterial genotype with a new allele combination 22 Transformation Bacteria can release their DNA (ex: after the cell death) which can be taken up by another bacteria directly from the extracellular environment. Occurs naturally when a bacteria recognizes a foreign DNA and transports it inside the cell Used in molecular biology laboratories to create new bacterial strains and clone a gene The new recombinant strain carries a plasmid with one or more genes of interest. Used for example in the production of the COVID19 vaccine! à copy the SARS-Cov2 spike protein gene into millions of copies 23 So… are bacteria good or bad?