Microbial physiology

• Microorganisms are a diverse group of organisms that include bacteria, actinomycetes, fungi and cyanobacteria and have interesting characteristics.
• In a large volume, remarkable quantities of energy are dissipating as heat.
• Under the usual conditions of culture, it is not often considered that a sufficient amount of heat may be produced to kill the cells.
• The gradual decline in the viable population appears to represent an acceleration of the effects of accumulation of toxic products, exhaustion of nutrients and perhaps other factors such as the generation of heat.
• Most microorganisms are devoid of chlorophyll with the exception of cyanobacteria and phototrophic bacteria which derived energy from light.
• Heterotrophic microorganisms depend on external sources to obtain their nutritional requirements.
• If microorganisms obtain nutrients from living host cells, they are known as parasites; on the other hand they are known as saprophytes if obtained their nutritional requirements from organic matter or dead materials.
• Microbial physiology is a branch of biology which deals with microbial activities and functions, how they affect their environment and how the environment affects them.
• Culture media are employed in the isolation, maintenance and identification of microorganisms.
• Liquid media are used for biomass production as well as physiological studies of microorganisms, while solidified media are used for isolation of pure cultures, morphological studies and a variety of other purposes.
• Complex media usually contain complex materials of biological origin such as blood or milk or yeast extract or beef extract or plant extracts, the exact chemical composition of which is obviously undetermined.
• Complex media are usually used for isolation of microorganisms and studying their morphological characteristics especially when used in the solidified state.
• Complex media usually provide the full range of growth factors that may be required by an organism.
• A selective medium is one which has a component(s) added to it which will inhibit or prevent the growth of certain types or species of microorganisms (especially in case of bacteria) and/ or promote the growth of the desired species.
• Differential medium allows the microbiologist to distinguish between different types of bacteria.
• Fungal growth is difficult to define as there is remarkable diversity in forms, ranging from microscopic unicellular as in yeast to large bodies as in basidiomycetes.
• An initial lag phase, during which cells do not divide, although cell enlargement and enhancement in their metabolic activity may occur, is a phase of microbial growth.
• The growth model of bacteria is the binary fission type which shows all phases of growth.
• Fungi exhibit remarkable diversity in forms, ranging from microscopic unicellular as in yeast to large bodies as in basidiomycetes.
• Apical growth of filaments is essentially a specialized feature of fungi.
• Growth can occur without cell division when cells are synthesizing storage compounds such as glycogen.
• In plasmodial growth, the protoplast may replicate anywhere in the plasmodium, so any small part of the plasmodium is capable of reproducing itself.
• Yeast type growth, characterized by a process known as budding, is mainly recorded in yeasts.
• Yeasts, which are unicellular fungi, could follow the same pattern of bacterial growth.
• The mechanism of apical growth involves both a degree of wall breakdown and a degree of wall synthesis.
• In filamentous fungi, the pattern of growth is not completely similar to that of bacteria.
• Under certain conditions, cell number remains constant, but the concentration of biomass continues to increase.
• Vesicles in the tips of septate fungi contain wall precursors, wall synthases and wall lytic enzymes, suggesting their functions in the apical growth.
• Growth kinetics of homogenous unicellular cultures can be modeled, but filamentous growth is much more complex.
• Microbial growth can be defined as an orderly increase in cellular components, resulting in cell enlargement and eventually leading to cell division.
• Staphylococcus aureus (common bacterial pathogen) can be isolated and identified by differential medium containing very high concentration of salt, mannitol as fermentable sugar and a pH indicator dye.
• Mannitol- fermenting colonies (S aureus) produce acid and react with the dye forming a colored halo around the colonies.
• Mannitol non- fermenters (Sepidermidis, non-pathogenic) do not form a halo around their colonies.
• Phase of autolysis or cell death.
• Growth in cell size and mass occurs during this period.
• Lag phase: Cell division is not taking place in this phase, but there is considerable metabolic and physiological activity in preparation for cell division.
• Exponential or logarithmic phase: Marked by cell division as a uniform and a maximum rate.
• During exponential growth, one cell produces two in unit time, two produces four, four produce eight, and so on, the process continuing until one of the nutrients become limiting, oxygen becomes depleted or metabolic products accumulate to toxic levels.
• The rate of growth during the logarithmic phase is termed the specific growth rate (µ) of the organism and calculated from the following equation: No=number of cells at any time (to) Nt=number of cells at sometime (t), Where 2.303 is the base of natural logarithms.
• The lag in cell division at the initial stage of the growth cycle is indicative of the fact that many adjustments must be made.