Microbial Nutrition

Microbial Nutrition

• Microbial nutrition is the process by which chemical compounds, or nutrients, are acquired from the environment to sustain life.
• Bioelements are basic requirements for life like carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, sodium, chlorine, and magnesium.
• Essential nutrients are substances such as elements or compounds that an organism must get from an outside source.
• Macronutrients are required in large quantities for cell structure and metabolism.
• Micronutrients or trace elements are required in small amounts, involved in enzyme function and maintenance.
• Organic nutrients contain carbon and hydrogen atoms and are generally products of living things.
• Methane (CH4), carbohydrates, lipids, proteins, and nucleic acids are organic nutrients.
• Inorganic nutrients are atoms or molecules that contain a combination of atoms other than carbon and hydrogen.
• Metals and their salts such as magnesium sulfate, ferric nitrate, and sodium phosphate, as well as gases like oxygen, carbon dioxide, and water are considered inorganic nutrients.
• 70% of cell content is water.
• Organic compounds make up 97% of the dry cell weight where proteins are the most prevalent.
• Six elements make up 96% of a cell: carbon, hydrogen, oxygen, phosphorous, sulfur, and nitrogen.

Essential Biological Nutrients

• Carbon, found in the air as CO2, sediments/soils, and living things, is produced by respiration, used in photosynthesis, and essential for structure and function.
• Nitrogen, found in the air as N2, soil and water as NO3 and NO2, the soil and water as NH3, and organisms as organic nitrogen, is available to microbes that can fix it into inorganics like nitrates, nitrites, and ammonium.
• Oxygen, found in the air as O2 and oxides, the soil, and water, is necessary for the metabolism of nutrients by aerobes as an element in inorganic compounds.
• Hydrogen is found in water, swamps, and mud in H2 gas, H20, H2S and CH4 gases, it is the most abundant compound in cells and a solvent for metabolic reactions where it is produced for usage by bacteria and archaea.
• Phosphorus is found in rocks, mineral deposits, and soil as Phosphate, a key component of DNA and RNA, critical to the genetic makeup of cells and viruses.
• Elemental sulfur is oxidized by some bacteria as an energy source and is found in vitamin B1.
• Potassium is found in mineral deposits, ocean water, and soil and plays a role in protein synthesis and membrane transport.
• Sodium is found the same way as potassium, and it is a major participant in membrane actions and maintains osmotic pressure.
• Calcium is found in oceanic sediments, rocks, and soil, a component of protozoan shells.
• Magnesium is found in geological sediments, rocks, and soil, and it is a central atom in the chlorophyll molecule required for membranes, ribosomes, and some enzymes.
• Chloride is found in ocean water and salt lakes and functions in membrane transport.
• Zinc is found in rocks and soil, acts as an enzyme cofactor and regulates eukaryotic genetics.
• Iron, in rocks and soil, is an essential element for the structure of respiratory proteins (cytochromes)
• Micronutrients include copper, cobalt, nickel, molybdenum, manganese, and iodine.
• Iron is required by microorganisms
• Ferric iron is very insoluble, making uptake difficult.
• Microorganisms secrete siderophores to improve iron uptake and then the complexes are transported into the cell.
• Growth factors are essential organic nutrients that cannot be synthesized by an organism due to a lack of genetic and metabolic mechanisms.
• These growth factors, such as essential amino acids and vitamins, must be provided as a nutrient for survival.

Classification of Nutritional Types

• Carbon and energy sources are main determinants of nutritional type.
• Heterotrophs obtain carbon from other organisms, whereas autotrophs use CO₂ as their source.
• Chemotrophs gain energy from chemical compounds and Phototrophs gain energy through photosynthesis.
• Chemoorganotrophs: Derive carbon and energy from organic compounds, i.e. aerobic respiration
• Saprobes are free-living microorganisms that feed on organic detritus from dead organisms.
• They can be opportunistic pathogens or facultative parasites.
• Parasites derive nutrients from a host and some of which are obligate.

Transport

• Passive transport does not require energy, substances in a gradient move from areas of higher concentration to lower concentration.
• Diffusion, osmosis (diffusion of water), and facilitated diffusion which requires a carrier.
• Active transport needs energy and carrier proteins, it is gradient independent.
• Carrier-mediated active transport, group translocation where transported molecules are chemically altered, and bulk transport for endocytosis, exocytosis, and pinocytosis.
• Tonicity pertains to water concentration and cell walls, where membranes can burst.

Environmental Factors

• A microbe's niche is the totality of adaptations the organisms make to their habitat.
• Environmental factors affect the function of metabolic enzymes.
• Influential factors include temperature, oxygen requirements, pH, osmotic pressure, and barometric pressure.
• The range of temperatures for microbial growth can be expressed as three cardinal temperatures: minimum, maximum, and optimum temperatures.
• Psychrophiles have an optimum temperature below 15°C and can grow at 0°C.
• Mesophiles have an optimum temperature between 20°C and 40°C, and are most human pathogens.
• Thermophiles have an optimum temperature greater than 45°C.
• When oxygen is utilized it transforms into toxic products known as Reactive Oxygen Species (ROS).
• Singlet oxygen (1O2), superoxide ion (O2-), peroxide (H₂O₂), and hydroxyl radicals (OH-)
• Most cells have developed enzymes to neutralize these chemicals. Superoxide dismutase, catalase/peroxidase
• Microbes not capable of dealing with toxic oxygen are forced to live in oxygen-free habitats.
• Aerobes utilize oxygen and can detoxify it.
• Obligate aerobes cannot grow without oxygen.
• Facultative anaerobes utilize oxygen and can also grow in its absence.
• Microaerophiles require only a small amount of oxygen.
• Anaerobes do not utilize oxygen.
• Obligate anaerobes lack the enzymes to detoxify oxygen so cannot survive in an oxygen environment.
• Aerotolerant anaerobes do not utilize oxygen, but can survive and grow in its presence.
• Neutrophiles grow at a pH between 6 and 8.
• Acidophiles grow at extreme acid pH.
• Alkalinophiles grow at extreme alkaline pH.

Other Factors

• Osmophiles need a high salt concentration.
• Obligate halophiles grow optimally in 25% NaCl solutions, but require at least 9% NaCl.
• Osmotolerant bacteria can live in high osmotic pressure, but do not require high concentrations of solute.
• Facultative halophiles are remarkably resistant to salt.
• Microbial relationships are dynamic and depend on several factors.
• Symbiosis exists when two organisms live together in a close partnership.
• Mutualism is where both members benefit and need each other for survival.
• Commensalism is where one organism benefits while the other is neither harmed nor benefitted.
• Parasitism is where the parasite is dependent and creates benefits while harming the host.
• Non-symbiotic organisms are free-living in a shared habitat.
• Syntrophy or cross-feeding is where microbes share a habitat and feed off substances released by other organisms.
• Amensalism exists when one member of an association produces a substance that harms or kills another.
• Biofilms form when organisms attach to a substrate with a matrix.
• They dominate the structure of most natural environments on earth.
• They communicate and cooperate in the formation and function of biofilms using quorum sensing.
• Our bodies support symbiotic bacteria, fungi, and a few protozoa.
• These relationships cause diversity, and impact our physiology, immunity, and genetics.