Biology 144 notes: Microbiology

Biology 144 notes: Microbiology - Microbial Diversity What is microbiology? Microbiology is the study of Organisms in the micrometre size range. Why microbes matter: - Ubiquitous – they occur in environments where no other life forms survive - Diverse capabilities with respect to oxygen use – some are capable of anaerobic growth - Critical role in the cycling of nutrients and functioning of ecosystems – the only organisms to fix nitrogen - Less complex than plants and animals – they were the first “basic” cell - Capable of horizontal gene transfer - Rapid growth rates – useful for industrial processes, research, and biotechnology - Diverse metabolic pathways – ‘metabolites’ used in medicine, industry, environmental protection, etc. - They have co-evolved with us, other animals, and plants – mostly useful interactions, but also capable of causing disease Basically, microbes sustain life on earth. They were he first inhabitants of our planet, creating oxygen through a photosynthetic process – without them the recycling of nutrients in the ecosystems would not be possible. Importance of microorganisms: - Prokaryotes – largely responsible for creating atmosphere and soil billions of years ago → Cyanobacteria produced oxygen through photosynthesis - Life on earth depends on the cycling of chemical elements between organisms and the physical environment → Nitrogen fixation [reduction of atmospheric nitrogen to ammonia] by prokaryotes is the only means of replenishing nitrogen sources used by most microorganisms and by all plants and animals → Organic compounds produced from carbon dioxide via photosynthetic plants, algae and prokaryotes serve as building blocks for heterotrophic organisms → Prokaryotes and fungi are involved in decomposition (carbon, nitrogen, phosphorus, sulphur, etc. are recycled) Diversity amongst microbes has been key to the evolution of life on earth. No other organisms display the adaptability they do. A necessary part of studying microbes is that we need to classify them – they mostly belong to the domains Bacteria and Archaea [prokaryotes], with the larger – often multicellular – fungi belonging to the domain Eukarya [eukaryotes]. Carl Woese’s 3-Domain system: Woese [pronounced like “rose”] used sequencing techniques to classify microbes, and discovered a whole new group, the Archaebacteria, that were more closely related to eukaryotes than to the true bacteria [eubacteria]. He proposed the tree-domain system. In Woese’s system, the earliest ancestral cell gave rise to two branches. One lead to the evolution of all the bacterial species, while the other brnch lead to the Archae (which split off first) and the Eukarya. Although there is one debate about how lineages arose, it is generally accepted that, timewise, Archae are the most ancient of the tree domains. [See below for Woese’s revised Tree of Life] Classification of microbes: - Scientists group organisms based on similarities → Phenotypic (morphology) and Genotypic (DNA homology) - We classify microbes based on both their morphology [appearance and biochemical properties] as well as the DNA sequence of key genes in their genomes - All organisms use ribosomes to translate mRNA into proteins, so every organism contains the genes for ribosomal RNA. A ribosome is made up of specific pieces of ribosomal RNA tightly bound to ribosomal proteins to make up the subunits of a ribosome - Evolution has resulted in small changes to the ribosomal gene sequence – enables us to compare species – but the changes are limited by the fact that the overall function of ribosomes must be maintained Taxonomic hierarchy: - Below are two examples of microbial classification – one for a yeast [Saccharomyces cerevisiae] and the other for a bacterium [Escherichia coli] Domain: Eukarya Bacteria Kingdom: Fungi Bacteria Phylum: Ascomycota Proteobacteria