19 Notes - Topic 19 Fundamentals of Microbiology...

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Unformatted text preview: Topic 19 Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld Learning Objectives: To understand the diversity of microbial groups within the Gram ­ positive Bacteria. We now consider the Gram ­positive bacteria. These organisms fall into two distinct phylogenetic groups, formerly termed low GC and high GC, based on their DNA GC base content, although these terms are rarely used now. The high GC group is currently known as the Actinobacteria; the low GC group is often sub ­divided into several groupings. As with the Proteobacteria, there are many examples of where traditional taxonomic groupings are at odds with phylogeny. Non ­sporulating, Gram ­positive bacteria (Firmicutes) (Tables 16.1 and 16.2) Staphylococcus and Micrococcus • Aerobic, catalase positive • Resistant to drying and high salt • Often pigmented • Staphylococci commonly found on animals (including human skin) • Micrococcus is actually a member of the Actinobacteria, but morphologically similar to the staphylococci Sarcina • Obligate anaerobes, cell division results in "packets" of eight cells, acid tolerant • Some species are among the few organisms that can grow in acid environment of the human stomach Lactic Acid Bacteria • Rods and cocci • Produce lactic acid as major fermentation product • No electron transport system, therefore no aerobic respiration  ­ substrate level phosphorylation only • Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld Anaerobes, but are aerotolerant (not sensitive to O2) • Most can only catabolize sugars • Complex nutritional requirements, limited biosynthetic capacity (fastidious) • Heterofermenters differ from homofermenters • Involved in many processes that are of human interest o Pathogens, fermented products, dental health Endospore ­Forming, Gram ­positive bacteria (low GC) (Table 16.4) This group includes all endospore ­forming bacteria. Their natural environment is the soil, and they are usually not pathogenic. Bacillus (Table 16.5) • Facultative or obligate aerobes • Can break down polymers (contrast with pseudomonads, which cannot) • Many produce antibiotics • Some species produce crystal protein toxins (Figure 16.6) that kill insect larvae  ­ ­ many are specific for a particular type of insect. • Some species can infect humans and other animals (e.g. Bacillus anthracis). Clostridium (Table 16.6) • Strict anaerobes  ­ ­ no electron transport system • Diversity of anaerobic fermentation (substrate and product) • Many industrially important products • Some fix N2 • Some produce toxins that cause human disease Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld Actinobacteria: Mycobacterium (high GC) (Table 16.8) • Contain lipids called mycolic acids (Figure 16.15) in the cell wall, • Exhibit acid ­fastness, a property in which the dye basic fuchsin is not removed by acid ­alcohol wash due to interaction of mycolic acids with the dye • Many are human pathogens • Resistant to many chemicals because of high lipid content of cell wall • Many contain pigments (carotenoids) Filamentous Actinobacteria: Streptomyces and relatives (high GC; Table 16.9) These nutritionally versatile organisms are filamentous, and form branching mycelia. Many of them form spores called conidia (Figures 16.20 and 16.21). These conidia are formed in sporophores, aerial filaments that are important in the classification of the organisms. Perhaps the best ­studied genus is Streptomyces, members of which are found mostly in the soil and produce many of the most important antibiotics (Table 16.10). Cyanobacteria division (Table 16.11) • Oxygenic, usually obligate aerobes, phototrophs • Gliding motility, no flagella • Contain chlorophyll A, which is the same type of chlorophyll found in chloroplasts • Morphologically diverse, ranging from unicellular to filamentous (Figure 16.24) • Some filaments contain differentiated cells called heterocysts distributed along the filament, which lack the O2 ­evolving photosystem II and in which N2 fixation takes place (Figure 16.26) • Heterocysts have a thick cell wall that slows the diffusion of O2 into the cell. ...
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This note was uploaded on 12/23/2011 for the course BIOL 140 taught by Professor Dr.joshneufeld during the Fall '10 term at Waterloo.

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