PHYSICAL FACTORS THAT AFFECT MICROBIAL GROWTH. Microbes can be separated into groups based on the range of temperatures at which they can survive. Preserving agents that increase the acidity of food, such as citric acid, are commonly added to help prevent bacterial growth and allow for longer storage. Temperature is one of those environmental parameters that limit the growth of species, including bacteria (Harley and Prescott 1999). Factors Affecting Microbial Growth. Alkalophiles have been isolated from soils, and most are species of the gram-positive genus Bacillus. The physical factors include the pH, temperature, Osmotic pressure, Hydrostatic pressure, and Moisture content of the medium in which the organism is growing. Extreme halophiles, such as Halobacterium, show optimum growth in conditions of 20 to 30 percent salt and will lyse (break open) if this salt level is reduced. The range for psychropiles is –10 degrees C to 20 degrees C, with an optimum at about 10 degrees C. The range for psychrotrophs is from 0 degrees C to 40 degrees C with an optimum of about 20 degrees C. Mesophiles like it best between 25 degrees C and 40 degrees C but can survive between 10 degrees C and 50 degrees C. Microbes that live within animals grow optimally at a temperature that matches that of their host. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Bacterial growth involves more than just a rate constant. When food is present, bacteria shift gears into a fast-growth mode, whereby they duplicate all their proteins quickly. On the other hand, environmental microbes have adapted to salty conditions; some grow quite well in low-salt environments, like seawater, or high-salt environments, like brine ponds. pH measures how acidic or basic (alkaline) a solution is, and microbes may grow in either acidic, basic, or neutral pH conditions. The authors investigate the bacterial population dynamics with the trade-off relationship between the growth rate and the growth yield or the death rate. The pH is the measure of how acidic or alkaline a solution is, with values from 0 to 14. The experiment was conducted in four different rooms from the 20th of November 2017 to the 16th of April 2018. Mesophilic bacteria are those in which optimum growth occurs between 20 and 45 °C (68 and 113 °F), although they usually can survive and grow in temperatures between 10 and 50 °C (50 and 122 °F). relationship between pH and bacterial growth is given in figure below. Growth of microorganisms in food is dependent on various parameters. When coal seams are exposed to air through mining operations, the pyritic ferrous sulfide deposits are attacked by A. ferrooxidans to generate sulfuric acid, which lowers the pH to 2.0 or even 0.7. In autecological studies, the growth of bacteria (or other microorganisms, as protozoa, microalgae or yeasts) in batch culture can be modeled with four different phases: lag phase (A), log phase or exponential phase (B), stationary phase (C), and death phase (D).. During lag phase, bacteria adapt themselves to growth conditions. Materials and Methods Bacteriocin activity Bacteriocin activity was detected by the deferred inhibition assay using lactic acid bacteria strains from fermented cassava and maize as … All microorganisms cannot grow in a single culture medium and in fact, many can’t grow in any known culture medium. Is It the Flu, Stomach Flu, or Traveler’s Diarrhea? Bacterial cells are remarkable machines. The most important physical factors are pH, temperature, oxygen, pressure, and salinity. Start studying Parameters that Affect Microbial Growth. 2 More. Here are the various groups of microbes based on their physical requirements: Psychrophiles are microbes that can grow at 0 degrees C. Some are inhibited at higher temperatures, preferring to live in cold climates, whereas others can survive in conditions above 20 degrees C. This latter group are called psychrotrophs because they prefer colder temperatures but can live just fine in higher ones. To describe the growth rate around the optimum and the maximum temperatures, Ratkowsky et al. The majority of psychrophilic bacteria are in the gram-negative genera Pseudomonas, Flavobacterium, Achromobacter, and Alcaligenes. Heat can kill microbes by altering their membranes and denaturing proteins. Some bacteria and archaea are acididophilic (acid loving); they grow in conditions far too acidic for other species. Colonies are described on the basis of size, shape, texture, elevation, pigmentation, and effect on growth medium. 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