Chapter 6: Microbial Nutrition and GrowthChapter 5 Summary- Metabolism: the set of controlled chemical reactions within cells- The ultimate outcome of metabolic activity is reproductiono Reproduction is an increase in the number of individual cells or organisms- Growth refers to an increase in the size of a population of microbes rather than to an increase in the size of an individual o Result is a discrete colony (an aggregation of cells arising from a singleparent cell) or a biofilm (a collection of microbes living on a surface in a complex community, typically in a liquid environment)o Begin with one and following metabolism and reproduction you may have one million organismsWhy Is This Important?- Microbial growth is a result of microbial metabolism- Different organisms require different nutrients for growth- Different organisms also require different growth conditions for growth (applications to human health)- Knowing what a microbe requires for growth allows us to grow them in the labGrowth Requirements- Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures- Most common nutrients – those containing necessary elements such a carbon, oxygen, nitrogen, and hydrogen- Microbes obtain nutrients from variety of sources and they must bring nutrients into their cells by the passive and active transport processes discussed in Chapter 3o Have to bring in from outside of the cell Sources of Carbon, Energy, and Electrons- Two groups of organisms based on source of carbono Autotrophs: inorganic source of carbon (carbon dioxide) Make organic compounds (contain C and H) from carbon dioxide such as glucose Not nutritionally dependent on other living things that do contain an organic source of carbono Heterotrophs: catabolize reduced organic molecules (proteins, carbohydrates, amino acids, and fatty acids; organic molecules containcarbon plus hydrogen) Dependent on other life forms to obtain these molecules- Two groups of organisms based on use of chemicals or light as a source of energyo Chemotrophs acquire energy from redox reactions involving inorganicand organic chemicalso Phototrophs use light as their energy sourceo Cells of all organisms require electrons or hydrogen atoms in order toOxygen Requirements- Oxygen is essential for obligate aerobes (final electron acceptor in ETC), but deadly for obligate anaerobes- How can this be true when neither atmospheric oxygen nor oxygen covalently bound in compounds is poisonous? o The forms of oxygen that are toxic are highly reactive and also excellent oxidizing agents o Resulting chain of oxidations causes irreparable damage to cells by oxidizing compounds such as proteins and lipids- Four toxic forms of oxygen1. Singlet oxygen: molecular oxygen with electrons boosted to a higher energy state  Phagocytic cells (certain WBC) use it to oxidize (strips electrons) pathogens o WBC hold oxygen in their peroxisomes mostly but also in their lysosomes  Occurs during photosynthesis so phototropic organisms have carotenoids that remove the excess energy of singlet oxygen2. Superoxide radicals: form during aerobic respiration (oxygen being the final electron receptor in the ETC) and anaerobic metabolism occurring in the presence of oxygen So reactive that aerobes must produce superoxide dismutases to detoxify themo If an organism lives in the presence of oxygen they have to have superoxide dismutases Anaerobes lack superoxide dismutase and die as a result of oxidizing reactions of superoxide radicals formed in presence of oxygeno The oxygen will strip it’s electrons until the cell dies3. Peroxide anion: formed during reactions catalyzed by superoxide dismutase and other reactions Aerobes contain either catalase or peroxidase to detoxify the peroxide anion Obligate anaerobes either lack both enzymes or have only a small amount of each that they aren’t effective 4. Hydroxyl radical: results from ionizing radiation (when cells are exposed to ionizing radiation) and from incomplete reduction of hydrogen peroxide The most reactive of the four toxic forms of oxygen Cells that produce catalase or peroxidase can also breakdown the hydroxyl radical Not a threat to aerobes due to action of catalase and peroxidase Oxygen Requirements- Aerobes: undergo aerobic respiration using oxygen as the final electron acceptor in the ETC; they have superoxide dismutase and catalase/peroxidase- Anaerobes: undergo anaerobic respiration using a molecule other than oxygen as the final electron receptor in the ETC- Facultative anaerobes: can maintain life via fermentation or anaerobic respiration or by aerobic respirationo They contain the enzymes needed to detoxify oxygen’s poisonous forms- Aerotolerant anaerobes: don’t undergo aerobic respiration (don’t use oxygen as a final electron receptor) but have some enzymes that detoxify oxygen’s poisonous forms- Microaerophiles: aerobes that require oxygen levels from 2-10% and have a limited ability to detoxify hydrogen peroxide and superoxide radicalso Atmospheric levels of oxygen are 21%Obligate aerobes grow where oxygen is the highestObligate anaerobes grow where oxygen is the lowestFacultative anaerobes grow throughout the tube, but more so at the top with oxygenAerotolerant anaerobes grow evenly throughout the tubeNitrogen Requirements- Anabolism often ceases due to insufficient nitrogen needed for proteins and nucleotideso Because there is not enough nitrogen around- Nitrogen acquired form organic and inorganic nutrients, plus all cells recycle nitrogen from amino acids and nucleotides- The reduction of nitrogen gas to ammonia (nitrogen fixation) by certain bacteria is essential to life on Earth because nitrogen is made available to living organisms in a usable form- Nitrogen is required for proteins, DNA, RNA, and ATPOther Chemical Requirements- Phosphorous is a component of phospholipid membranes, DNA, RNA, ATP, and some proteins- Sulfur is a component of sulfur-containing amino acids (cysteine and methionine), disulfide bonds critical to tertiary structure of proteins, and in vitamins (thiamin and biotin)- Trace elements – only required in small amounts; usually found in sufficient quantities in tap water (cobalt, copper, manganese, molybdenum, nickel, selenium, silicon, tungsten, vanadium, and zinc)o Periodic tableo Pure elements- Growth factors – necessary organic chemicals (contains C and H) that can’t