ELEMENTS OF MICROBIAL NUTRITION, ECOLOGY, & GROWTH Chapter 7 ELEMENTS OF MICROBIAL NUTRITION, ECOLOGY, & GROWTH

Microbial Nutrition, Ecology & Growth Sources of Nutrition - Nutrition consists of taking in chemical substances (nutrients) and assimilating and extracting energy from them Essential nutrients – substances required for survival; can be macronutrients or micronutrients Macronutrients are required in relatively large quantities and play principal roles in cell structure and metabolism Carbon - supplied in media as either carbohydrates (sugars) and/or peptones Nitrogen, sulfur, and phosphorus - needed for proteins & nucleic acids; supplied as peptones Micronutrients, or trace elements are present in smaller amounts and are involved in enzyme function and maintenance of protein structure Trace elements (Fe, Cu, Mg, and Zn) - needed for coenzymes; usually present in water

Microbial Nutrition, Ecology & Growth Organic nutrients contain carbon and hydrogen atoms and are usually the products of living things Organic growth factors - needed by fastidious (have special growth requirements) organisms Essential compounds not synthesized by organisms Supplied in media in purified form or as body fluids (e.g. blood, serum, etc.) Examples: vitamins, amino acids, purines, pyrimidines, hemin, NAD, etc. Inorganic nutrients are atoms or simple molecules that contains a combination of atoms other than carbon and hydrogen

Nutritional Categories An autotroph depends on carbon dioxide for its carbon needs If its energy needs are met by light, it is a photoautotroph, but if it extracts energy from inorganic substances, such as soil and minerals, it is a chemoautotroph A heterotroph acquires carbon from organic molecules A saprobe is a decomposer that feeds upon dead organic matter A parasite feeds from a live host and usually causes harm Disease-causing parasites are pathogens

Saprobes

Requirements for Growth Environmental factors - can be used in selective isolation Temperature - range and optimum different for each species; related to protein (enzyme) stability Psychrophile (cold loving) - 5 C - 30 C Mesophile - 10 - 45 C Thermophile - 25 - 95 C

Requirements for Growth pH - range and optimum differ with organism; most = 6.5-7.5; buffers used in media to maintain pH in proper range Acidophiles prefer lower pH Alkalinophiles prefer higher pH Osmotic pressure (solute concentration) - maintains water conc.; most cells require isotonic (0.9%) solutions; some can tolerate hypertonic (halophiles - e.g. vibrios & staphylococci) and hypotonic solutions; used as preservatives

Requirements for Growth Oxygen - requirements based on presence of catalase, peroxidase and superoxide dismutase (enzymes that handle toxic by-products) Source = atmosphere or chemical (organic or inorganic) Classification based on oxygen requirement Strict (obligate) aerobes - use molecular oxygen; have catalase and dismutase - e.g. Pseudomonas Strict (obligate) anaerobes - free oxygen is toxic; use inorganic oxygen-containing salts; generally lack both catalase and dismutase - e.g. Clostridium Facultative anaerobes - prefer molecular oxygen but can grow without it; have catalase and dismutase - e.g. Escherichia Aerotolerant anaerobe - cannot use oxygen but not killed if exposed; have dismutase - streptococci Microaerophilic - grow best at low oxygen tension; lack cytochromes; lack catalase but have dismutase; Campylobacter

Transport Mechanisms A microbial cell must take on nutrients from its surroundings by transporting them across the cell membrane Passive transport involves the natural movement of substances down a concentration gradient and requires no additional energy (diffusion)

Osmosis is diffusion of water through a selectively permeable membrane

Form of passive transport that can move specific substances is facilitated diffusion

Diffusion

Transport Mechanisms Osmotic changes that affect cells are hypotonic solutions, which contain a lower solute concentration, and hypertonic solutions, which contain a higher solute concentration Isotonic solutions have the same solute concentration as the inside of the cell

In active transport, substances are taken into the cell by a process that consumes energy

In group translocation, molecules are altered during transport

Transport Mechanisms Phagocytosis and pinocytosis are forms of active transport in which bulk quantities of solid and fluid material are taken into the cell

Microbial Growth Definitions Growth - increase in numbers Binary fission - method of reproduction used by prokaryotes in which each cell divides; doubles population (logarithmic)

Microbial Growth Generation time (doubling time) - time required for a cell to divide and multiply (double) its population (20 min. - 72 hrs.)

Phases of growth Lag - occurs at inoculation; little or no change in numbers; enzymes being synthesized and cells increasing in size preparing to divide; time increased if media is cold Log or exponential - cell mass and number increases in logarithmic manner; consistent rate and activity; organisms are most sensitive to adverse conditions Stationary - population stabilizes; production = death; may be due to accumulation to toxic wastes or decrease in nutrients Death (logarithmic decline) - deaths exceed production; cells usually most resistant and often assume unusual shapes (pleomorphic)