Growth requirements

Growth Requirements

• Most common nutrients contain necessary elements (carbon, oxygen, nitrogen, and hydrogen)

• Microbes obtain nutrients from variety of sources

Growth Requirements

Sources of carbon, energy, and electrons– Two groups of organisms based on source of carbon

• Autotrophs• Heterotrophs

– Two groups of organisms based on source of energy• Chemotrophs

– Phototrophs

Figure 6.1 Four basic groups of organisms

Growth Requirements

Oxygen requirements– Aerobes - are completely dependent on atmospheric O2 for

growth– Anaerobes - do not tolerate O2 and die in its presence– Facultative anaerobes - do not require O2 for growth, but do grow

better in its presence– Aerotolerant anaerobes - ignore O2 and grow equally well

whether it is present or not– Microaerophiles - are damaged by the normal atmospheric level

of O2 (20%) but require lower levels (2 to 10%) for growth

Figure 6.3 Oxygen requirements of organisms-overview

Growth Requirements

Nitrogen requirements– Anabolism often ceases because of insufficient

nitrogen– Nitrogen acquired from organic and inorganic

nutrients – All cells recycle nitrogen from amino acids and

nucleotides– Nitrogen fixation by certain bacteria is essential to

life on Earth

Key bacteria for nitrogen cycle

• Nitrosomonas convert ammonia to nitrite• Nitrobacter convert nitrite to nitrate. • Pseudomonas convert nitrate to nitrogen gas. • Azotobacter and Rhizobium are nitrogen-fixing

bacteria which fix nitrogen from the atmosphere and make it available to leguminous plants,

Growth Requirements

Other chemical requirements– Phosphorus – Sulfur– Trace elements

• Required only in small amounts– Growth factors

• Necessary organic chemicals that cannot be synthesized by certain organisms

Growth Requirements

• Physical Requirements– Temperature

• Effect of temperature on proteins• Effect of temperature on membranes of cells and

organelles– If too low, membranes become rigid and fragile– If too high, membranes become too fluid

Figure 6.4 Microbial growth-overview

Figure 6.5 Four categories of microbes based on temperature ranges for growth

Psychrophiles

Mesophiles

Thermophiles

Hyperthermophiles

Gro

wth

rate

Temperature (°C)

Figure 6.6 An example of psychrophile-overview

Growth Requirements

• Physical Requirements– pH

• Organisms are sensitive to changes in acidity – H+ and OH– interfere with H bonding

• Neutrophiles grow best in a narrow range around neutral pH (5.5 – 8.0)

• Acidophiles grow best in acidic habitats– pH between 0-5.5

• Alkalinophiles live in alkaline soils and water– pH between 8.5 and 11.5

Growth Requirements

• Physical Requirements - water– Bacteria are about 80-90% water– require moisture because they obtain most of their nutrients

from their aqueous environment– Use water to dissolve enzymes and nutrients– important reactant in metabolic reactions– Most cells die in absence of water

• Some have cell walls that retain water• Endospores and cysts cease most metabolic activity

Growth Requirements

• Physical Requirements - water– Osmotic pressure

• Pressure on a membrane by a solution containing solutes that cannot cross membrane

• Hypotonic - osmotic lysis can occur• Hypertonic - cell shrinkage called plasmolysis

– the addition of salts or other solutes to a solution inhibits food spoilage by bacteria

– as occurs when meats or fish is salted

• Restricts organisms to certain environments– Obligate and facultative halophiles (salt environments)

Growth Requirements

• Physical Requirements – water – Hydrostatic pressure

• Water exerts pressure in proportion to its depth

• Barophiles live under extreme pressure– Their membranes and enzymes depend on pressure to

maintain their shape

Associations and Biofilms

• Organisms live in association with different species– Antagonistic relationships– Synergistic relationships– Symbiotic relationships

Associations and Biofilms

• Biofilms – complex relationships among many microorganisms– Develop an extracellular matrix

• Adheres cells to one another• Allows attachment to a substrate• Sequesters nutrients• May protect individuals in the biofilm

– Form on surfaces often as a result of quorum sensing• a system of stimulus and response correlated to population

density• coordinate gene expression according to the density of their

local population– Many microorganisms more harmful as part of a biofilm

Figure 6.7 Plaque (biofilm) on a human tooth

• There is no single medium or set of physical conditions that permits the cultivation of all bacteria,

• many species are quite fastidious, requiring specific ranges of pH, osmotic strength, temperature and presence or absence of oxygen

• The requirements for growth of bacteria under laboratory conditions are determined by trial and error