BIOL 351 Microbiology Lecture 20 PDF

Welcome to Biol 351: Microbiology Dr. Ranjani Murali School of Life Sciences UNLV “The role of the infinitely small in nature is infinitely large” Louis Pasteur Lectures Lectures 1-5 6-18 Lectures Lectures 23, 2...

Welcome to Biol 351: Microbiology Dr. Ranjani Murali School of Life Sciences UNLV “The role of the infinitely small in nature is infinitely large” Louis Pasteur Lectures Lectures 1-5 6-18 Lectures Lectures 23, 24 18-22  Outline of Lecture 20 Symbiosis - a cooperative interaction Microbial syntrophy - metabolic cooperation between microorganisms ○ Lichens ○ A deep-sea methane fueled syntrophy Plant-microbe symbiosis - leguminous plants Insect-microbe symbiosis - mealy bug symbiosis Evolutionary concepts in endosymbiosis Microbial symbioses - Lichen  Lichens are an example of microbial symbioses Lichens are formed by symbioses between fungi and photosynthetic bacteria or algae. Foliose Fungi are good at attaching to a solid substrate and sometimes extracting nutrients from the Fructicose substrate with lichen acids. Algae or cyanobacteria provide fixed carbon. Crustose Sometimes lichen also have nitrogen-fixing bacteria as Brock, 16th edition symbionts. Lichens are an example of microbial symbioses Lichens are formed by symbioses between fungi and photosynthetic bacteria or algae. Fungi are good at attaching to a solid substrate and sometimes extracting nutrients from the substrate with lichen acids. Algae or cyanobacteria provide fixed carbon. Sometimes lichen also have nitrogen-fixing bacteria as Grimm et al., Frontiers in Microbiology, 2021 symbionts.  How is the symbioses propagated? During asexual reproduction, fungal propagules are released with the photobiont, and dispersed. The symbiotic relationship is preserved. During sexual reproduction, fungal spores are released without the photobiont. This allows for the acquisition of a new symbiont. Carrignon et al., wiki.santafe.edu (2017) Microbial symbioses - a methane-based syntrophy in the deep sea Chemosynthesis and the adaption of life to deep-sea environments Methane oxidizers are primary producers in deep sea ecosystems in the same way as photosynthetic organisms are on the surface. Obligate syntrophic partnership between ANME and SRB CH4+SO42-+H+→ CO2 +HS-+2H2O, ΔG0’=-18 kJ/mol AOM is performed by anaerobic methanotrophic archaea (ANME) in syntrophy with sulfate reducing bacteria (SRB). The thermodynamically unfavorable reaction of anaerobic oxidation of methane is only made possible because it is coupled to the highly favorable reaction of sulfate reduction. Microbial syntrophy Microbial syntrophy is a ‘nutritional situation in which two or more organisms combine their metabolic capabilities to catabolise a substrate that cannot be catabolised by either one of them alone’ (Stams & Plugge, 2009).  The multicellular consortia formed by ANME-SRB is another biofilm Myxococcus xanthus Geobacter sulfurreducens Pseudomonas aeruginosa ANME-SRB consortia Stephen CS, LaBelle EV, Brantley SL, Bond DR (2014) McGlynn SE, et al. AEM (2018) What is in a biofilm? Structural function - polysaccharide matrix and proteins. Surface binding - adhesins; pili. Proteins facilitating intercellular recognition. You can look at spatial structure using fluorescent microscopy and, spatial structure and composition using TEM.  What drives ANME-SRB syntrophy? Chadwick et al. PLOS Biology(2022) The syntrophy is driven by direct interspecies electron Murali et al. PLOS Biology(2023) transfer (DIET) mediated through a conductive biofilm  Stable isotope probing and nanoSIMS Alcolombri et al. ISME Communications (2022) NanoSIMS looks at single-cell activity with the incorporation of stable isotopes for e.g. 13C-labelled carbon and 15N-labeled nitrogen.  Fixed nitrogen transfer in ANME-SRB syntrophy When 15N labelled N2 is provided to ANME-SRB multicellular consortia, both archaea and bacteria incorporate 15N-N2, demonstrating that they can fix nitrogen. Further ANME often fixes nitrogen and provides organic nitrogen (as amino acids) to its sulfate reducing partner. Metcalfe et al. ISME (2020) Convergent evolution of methane-fueled syntrophy Multiple lineages of ANME and SRB convergently evolved to create this syntrophic partnership. Convergent evolution is identified using metagenomics and phylogeny. Chadwick et al. PLoS Biology(2022) Murali et al. PLoS Biology (2023) Mapping the conservation of important pathways in syntrophic SRB and evolutionary neighbors The presence and absence of genes are noted using comparative metagenomics. Evolution of syntrophic SRB from free-living SRB Murali et al. PLoS Biology (2023) Plant-microbe symbioses - nitrogen fixing bacteria in legumes Plant symbiosis - Nitrogen fixing bacteria in root nodules Legumes are flowering plants that bear their seeds in pods and include soybeans, clover, alfalfa, beans, and pea. Nitrogen fixing bacteria are found as symbionts in root nodules of legumes. Rhizobial infection forming root nodule in soybean plants. Brock (16th edition) Most rhizobial species are from α- and β- proteobacteria Rhizobial infection forming root nodule. Brock (16th edition)  Biochemistry in root nodules Brock (16th edition) 1. Recognition of the correct partner by both plant and bacterium and attachment of the bacterium to the root hairs. [Ricadhesin on bacterial surfaces and lectins on the plant surface] 2. Secretion of oligosaccharide signaling molecules (Nod factors) by the bacterium. 3. Bacterial invasion of the root hair. 4. Movement of bacteria to the main root by way of the infection thread. 5. Formation of modified bacterial cells (bacteroids) within the plant cells, development of the -fixing state, and continued plant and bacterial cell division forming the mature root nodules.  Regulation in root nodule formation Nod and Myc factors act in a two-factor signaling system. Leading to the formation of nodules. Brock (16th edition)  Regulation in root nodule formation Nod and Myc factors act in a two-factor signaling system. Leading to the formation of nodules. Brock (16th edition) Insect-microbe symbioses  Insect symbioses - Mealybug and the tripartite symbioses Mealy bugs feed on Bacteriocyte juices from green house plants ‘Candidatus Trabutinella endobia’ within ‘Ca. Trembalaya phenacola’ Szabó et al. ISME J (2017) Insect symbioses - Mealybug and the tripartite symbioses Genes from the mealy bug and Tremblaya together produce the peptidoglycan on the surface of Tremblaya’s endosymbiont. Bublitz et al. Cell (2019) Many γ-proteobacteria are insect symbionts Species of the genus Sodalis that are symbionts of insects are compared with species that are free-living. McCutcheon, Boyd and Dale, Cell (2019) Endosymbiont - genome size reduction Endosymbiont genomes are 1) Reduced in size 2) And develop a bias towards A+T bases The latter is an indication of increasing genome stability. This is counter to the standard G+C bias in selection and recombination (G+C rich templates’ recombination is favored.) McCutcheon, Boyd and Dale, Cell (2019)