Elements of Microbial Nutrition, Ecology and Growth

1. Elements of Microbial Nutrition, Ecology and Growth Chapter 7

2. Microbial physiology is the study of vital life processes representative of all organisms Nutritional needs Metabolic pathways Environmental conditions necessary and inhibitory to life itself Every life form strives to live, reproduce to make more like itself In 24 hours, a single bacterium with adequate water, nutrients, and favorable conditions can produce progeny more numerous than all the humans on Earth!

3. Nutritional Requirements Nutrients are chemical substances used in metabolism and growth Source of energy Source of ‘building blocks’ to make cellular materials Different organisms require different nutrients in different amounts All organisms share common elements of nutrition

4. Nutrients Nutrients may be required in various amounts, for various uses Macronutrients – required in large quantities; important in cell structure and metabolism proteins, carbohydrates, lipids Micronutrients or trace elements – required in small amounts; involved in enzyme function & maintenance of protein structure manganese, zinc, nickel Essential Nutrients are materials that cannot be synthesized by an organism but necessary to sustain life must be supplied by the diet. essential amino acids essential fatty acids vitamins

5. Chemical composition of cytoplasm Cellular analysis of E. coli 70% water 96% of cell is composed of 6 elements Carbon -- Nitrogen Hydrogen -- Phosphorous Oxygen -- Sulfur Organic compounds account for 97% dry weight Organic nutrients contain carbon and hydrogen atoms and are the products of living things Hydrocarbons like methane (CH4) Macromolecules including carbohydrates, lipids, proteins, and nucleic acids Inorganic nutrients– metals and their salts (Potassium, Calcium, Sodium, Magnesium, Iron) gases (oxygen, carbon dioxide) water

6. Prokaryote complexity Analysis of E. coli shows the nutritional and metabolic complexity of prokaryotes when compared to eukaryotes Remember that eukaryotes are more structurally complex Cytoplasm contains over 5000 different compounds Growth requires only a few nutrients in diet Very diverse synthesis capability

7. Nutrient sources may be both biotic and abiotic Environmental sources of nutrients include: Air (79% N2, 20% O2) Water (essential to metabolic processes) Soil (minerals) Other organisms serve as nutritional sources. Saprobes – decompose dead organisms (detritus) Parasites – utilize tissues and fluids of a living host and cause harm

8. Significance of Carbon Carbon is a component of all biological cells Both organic and inorganic carbon sources Molecules of carbon function as: energy sources structural components (cell building) Heterotrophs – organisms that must obtain carbon in an organic form feed on other organisms or the products of other organisms metabolism Autotrophs - organisms that use CO2, an inorganic gas, as its carbon source

9. Energy All organisms require energy to drive cellular processes Extraction of energy from organic nutrients is major role of metabolism Some organisms acquire energy from other sources (light, inorganic compounds) Prokaryotes are categorized by their source of carbon and source of energy all combinations exist (eukaryotes are NOT as diverse)

11. Nitrogen Main reservoir is atmospheric nitrogen gas (79% N2) Nitrogen is a structural component of Proteins, Nucleic Acids Some microbes use inorganic N compounds, (NO3-, NO2-, or NH3) Some bacteria can fix N2 N must be converted to NH3 (ammonia) before it can be combined with carbon Oxygen O2 makes up 20% of atmosphere Major component of organic compounds Essential to metabolism of many organisms Component of inorganic salts (sulfates, phosphates, nitrates) & water Metabolic uses involve Redox Rx’s, Final Electron Acceptors. Hydrogen Major element in ALL organic compounds & several inorganic ones (water, salts & gases) H gases are produced & used by microbes Enterics produce H2 by fermentation Methanogens combine H2 with CO2 Roles of hydrogen include: maintaining pH forming H-bonds between molecules Phosphorous Main inorganic source is phosphate (PO4-3), phosphoric acid (H3PO4) found in rocks & oceanic mineral deposits Key component of nucleic acids (DNA, RNA) Universal function in energy transfers (ATP) Sulfur Widely distributed in environment, rocks, sediments contain sulfate, sulfides, hydrogen sulfide gas and elemental sulfur Essential component of some vitamins and amino acids Contributes to stability of proteins by forming disulfide bonds (S – S bridges

12. Nutrients are absorbed by various physical and physiological mechanisms Transport -- movement of substances across the plasma membrane Passive transport – does not require energy, follows concentration gradient Diffusion-O2, CO2 are transported freely Osmosis – passive transport of water isotonic-zero net hypotonic-very low solute in environment adaptations prevent rupture hypertonic-high solute, brine antimicrobial adaptations include absorption of salt to balance intake Facilitated diffusion – passive, but requires a membrane protein protein provides channel or changes shape to allow passage polar molecules like H2O, glucose

13. Active Transport Carrier-mediated active transport requires energy and membrane proteins gradient independent transport at greater rates ‘pumps’ molecules across against conc. gradient

14. Environmental Factors Environmental factors affect rate and amount of growth, survival depends on adaptation to changing environments Factors include: Temperature Oxygen availability pH Electromagnetic radiation Barometric and Osmotic pressures In nature, these factors fluctuate, in lab, conditions are controlled

15. Temperature Fluctuations in temperature affect metabolism and morphology Temperature is factor in rates of metabolism and transport, protein configuration Most microbes are adapted to narrow temperature range, some to wide ranges Some microbes adapted to extreme temperatures Most adapted to ‘mid’ range temperatures

16. 3 Cardinal Temperatures Minimum Temperature – lowest temperature that permits a microbe’s growth and metabolism Maximum Temperature – highest temperature that permits a microbe’s growth and metabolism Optimum Temperature – promotes the fastest rate of growth and metabolism

17. Temperature Range Adaptations Psychrophiles – optimum temperature below 15oC, capable of growth at 0oC Mesophiles – optimum temperature 20o-40oC, most human pathogens Thermophiles – optimum temperature greater than 45oC

18. Availability and Utilization of O2 Many organisms use (require) oxygen in respiratory pathways Some organisms are poisoned by oxygen Oxygen is a strong oxidizing agent Singlet oxygen, superoxide ion, peroxide, and hydroxide radicals are toxic Cellular damage occurs when molecules are oxidized Adaptations involve enzymes that detoxify and neutralize the oxidizing agents Catalase and superoxide dismutase Some environments are devoid of oxygen, others have an abundant supply Other environments have intermediate levels

19. Tests for Oxygen Requirements

20. Effects of pH Most microbes adapted to near neutral ranges (6 – 8 pH) Acids and bases can damage cellular components Fungi are more tolerant of lower pH than bacteria Some are adapted to extreme ranges Acidophiles are adapted to very low range (0 – 2 pH) Alkalinophiles (ranges up to 10 pH) are found in alkaline soils

21. Pressure Osmotic pressure determines tonicity Relative solute in the environment Hypertonic solutions are antimicrobial plasmolysis, crenation Halophiles are adapted to high level of salt Hydrostatic (barometric) pressure Barophiles are adapted to high barometric pressure

22. Microbial associations Symbiosis – close nutritional relationships between organisms Essential and beneficial to at least one member Mutualism – both members benefit Examples protozoa digests cellulose for termites bacteria breakdown cellulose for ruminates E. coli produces vitamin K in large intestine

23. Commensalism – commensal benefits, other member unharmed feed on dead cells, residual food in mouth, etc. Satellitism — a dependent form of commensalism one provides growth factors for other or break down toxins Parasitism – parasite benefits; host is harmed What is a facultative parasite?

24. Other microbial associations Non-symbiotic – organisms are free-living; relationships not required for survival Synergism – members cooperate and share nutrients, non-essential Biofilms are cooperatives of many different organisms Antagonism – one member is inhibited or destroyed by another, competition for resources

25. Microbial Growth Where animal growth refers to an increase in size from egg to larva, from newborn to adult a single organism begins as one cell and grows into many Bacteria ‘grow’ by an increase in population size one cell divides to become 2 cells, identical to the original, clones of each other Reproduction is asexual better referred to as multiplication Cell division by Binary Fission

26. Rate of Population Growth Different bacterial species divide at different rates (minutes to days) Generation Time is the time elapsed between formation of a new daughter cell and the time when it divides to form 2 new cells. The population doubles with each generation.

27. Exponential Growth Logarithms are used to describe the rate of increase in bacterial populations. The exponent represents the number of generations Population size is calculated using the equation: Nf = (Ni)2n

28. Nf = (Ni)2n Nf equals the final number of cells Ni equals the initial number of cells n equals the number of generations that have occurred in a given elapsed time

30. Normal Growth Curve a graphical representation of changes in population size over time in liquid medium at constant temperature Four stages in the Normal Growth Curve Lag phase Log phase Stationary phase Death phase

31. Normal Growth curve

32. Normal Growth Curve Lag phase – “flat” period of adjustment; little growth Exponential growth phase – a period of maximum growth will continue as long as cells have adequate nutrients & a favorable environment Stationary phase – rate of cell growth equals rate of cell death, caused by depleted nutrients & O2, excretion of organic acids & pollutants Death phase – as limiting factors intensify, cells die exponentially in their own wastes

33. Measurement of bacterial growth Direct, total counts Dead cells counted along with viable cells Flow cytometer Automated, sensitive Turbidity Photo detector measures intensity of light passing through cloudy tube