1-2 - Evolution and Diversity of Microbes -.pdf

1-2: A Diverse World of Microbes Lecture Overview: • Introduction to the world of microbiology, evolution and diversity of microbes, and their important roles in our lives • Textbook: Chapter 1, I & Chapter 13, I/II Microbes (microorganisms): Life too small to be seen by the human eye Often singl...

1-2: A Diverse World of Microbes Lecture Overview: • Introduction to the world of microbiology, evolution and diversity of microbes, and their important roles in our lives • Textbook: Chapter 1, I & Chapter 13, I/II Microbes (microorganisms): Life too small to be seen by the human eye Often single celled organisms (but not always!) from the three domains of life cause O diseases Nume Bacteria - Primary emphasis of this course Archaea - “extremophiles” and more!! ↳ mostly prokaryotes Prokaryotes Eukaryotic microbes Examples: - Algae - Molds (fungi) - Plasmodium spp. (cause of malaria) Viruses o Viruses are genetic elements (DNA, RNA) that can only multiply within a living cell. Infect (hijack) cells to reproduce. o Viruses are sometimes included in field of microbiology, sometimes considered separately in “virology” o Viruses are NOT discussed in this course o Fundamentally different form of life(?) from other microbes o Obligate parasites. Not cells. o Lack hallmarks of cellular life (metabolism, ribosomes). o IMIN 324: Basic Virology is the intro course for viruses The three domains of life Also extremely diverse! Textbook Fig. 1.10 Animals Unicellular microbes Plants Current life on earth Textbook Fig. 13.9 How did we get here? Where did all this diversity come from??? Bacteria Eukarya Archaea ~ 2 bya LUCA RNA World (?) > 3.5 bya! RNA world hypothesis Within some stable “compartments” with high concentrations of organic building blocks: Modified from Le Vay and Mutschler, emerging topics in life sciences, 2019 Some evolutionary forces start to kick in: o Improved replication o Simple functions (stability, binding other molecules) o More complex functions (enzymes) RNA world hypothesis Simple RNA molecules - More stable - Self-replicating - Simple functions Simple ribosomes Bind/interact with/use amino acids & peptides RNA + protein world. More and more complexity - DNA - “Membranes” (compartmentalization) RNA world hypothesis - evidence RNA can form intricate, stable structures that can: o Carry out a wide range of chemical reactions o Specifically bind many molecules Proteins are still made today using RNA components o tRNA o The active component of ribosomes is a catalytic RNA (proteins = accessory factors, RNA = core of ribosome). Many apparent “relics” from RNA world o Common biological molecules with ribonucleotide components (see next slide) o Various ribozymes (RNA enzymes), riboswitches (mRNA “receptors” that bind ligands – regulate gene expression), the ribosome itself! Universal, essential biological molecules are mostly nucleotide-based Horning DP, 2011, doi.org/10.1007/978-3-642-11274-4_1740 Last Universal Common Ancestor (LUCA) We don’t know exactly what LUCA was. Some presumed features: • DNA replication, transcription, translation, cell division • ATP served as energy intermediate • Lipid bilayer membrane. • Anaerobic metabolism (no oxygen!) – likely used H2 as energy source, CO2 as carbon source A limited number of genes (e.g. ribosomal RNA) in all modern organisms. Most or all of these presumably from LUCA The rise of oxygen on earth - Phototrophs Where do microbes get their energy? Chemotroph: Derive energy from releasing bond energy from chemical compounds Phototroph: Absorbs light, transforms it into chemical energy The rise of oxygen on earth • For the first ~ 2 billion years on earth, the atmosphere was devoid of oxygen (“anoxic”) • Rise of photosynthetic bacteria that producing oxygen as a waste product (cyanobacteria) - oxygenic photosynthesis – O2 in atmosphere • Oxygen is a great electron acceptor – gave rise to aerobic organisms - efficient energy production – complexity! • Ozone (O3) layer – protects vs. UV (lethal to cells, damages DNA) – makes surface of planet more easily habitable Textbook Fig. 13.1 Evolution of Eukarya: The endosymbiotic theory • Eukarya lineage evolved from an archaea-like ancestor that engulfed an aerobic respiring bacterium (phylum Alphaproteobacteria) • Became an endosymbiont (organism living within another organism in symbiotic relationship) and ultimately the mitochondria -- efficient energy production. • Transferred many bacterial genes into host organism • Plants emerged in a second event when an engulfed photosynthetic bacterium (cyanobacterium) became basis for the chloroplast Evolution of Eukarya: The endosymbiotic theory Serial endosymbiosis hypothesis Symbiogenesis hypothesis Textbook Fig. 13.10 Evidence of endosymbiotic theory • DNA replication, transcription, translation machinery of eukaryotes more similar to archaea than bacteria • Mitochondria and chloroplasts: • Have their own genomes, ribosomes, tRNA • This machinery is bacterial • Sequence comparisons -- mitochondria related to ⍺Proteobacteria, chloroplasts related to Cyanobacteria For most of earth’s history, it has been a microbial planet (it still is!) o Number of microbes on earth estimated to be ~1 x 1030 o Number of animals on earth (mostly invertebrate) estimated to be ~2 x 1019 o There are ~50,000,000,000 microbes for every animal (that’s a lot!) o 1g of soil can contain ~1010 bacteria, ~50,000 different species Textbook Fig. 1.10 A large proportion of life on earth is microbial o Despite their small size, microbes make up a significant amount of the biomass on earth Animals make up well under 1% of biomass! Textbook Fig. 1.12 Microbes are ubiquitous o Microbes are prevalent in virtually every habitat on earth o This includes many extreme and harsh environments Textbook Table 1.2 Microbes live in diverse communities o Microbes live in complex and competitive microbial communities o Microbial interactions take all forms. Can be fiercely competitive…can be obligately symbiotic (and everything in between) o Communities (and microbes themselves!) can evolve quickly – fierce battles over nutrients o Competition drives evolution and diversity Some images of microbial communities Textbook Fig. 1.1 People are part-microbe too! o Microbes inhabit our bodies – e.g. our skin, our mouths, our intestinal tract o Our bodies have roughly the same number of microbial and human cells!! More microbial genes than human genes! Textbook Fig. 1.15 Microbes (even prokaryotes) come in many shapes and sizes o We tend to think of microbes as all looking similar. They don’t. o Come in different shapes, sizes, vastly different surfaces o (To a microbe, we probably look just like a squirrel!) Textbook Fig. 13.1 Some common prokaryotic cell morphologies – textbook Fig. 1.8 Microbes have a major impact on our lives Textbook Fig. 1.2 Microbes & disease o We have made great strides in combating microbial diseases o Still a major global health problem (particularly in developing world). Huge health/economic impact. o Rise of antibiotic resistance threatens our progress Causes of death in the USA in 1900 vrs. today -- Textbook Fig. 1.13 We use microbes in many ways Use of microbes in industry and biotechnology is an expanding field with an exciting future Textbook Fig. 1.17 Many of our favourite foods are made using microbial fermentation Textbook Fig. 1.16