MICROBIAL GROWTH

• It is then weighed.
• Bacteria grow quickly in batch culture (enclosed vessel), and cell numbers increase dramatically in a short period of time.
• As one cell divides to become two cells, this is expressed as 2 0 – 2 1.
• The microbial growth cycle consists of four phases: Lag phase, Exponential or Log phase, Stationary phase, and Death phase.
• Each daughter cell receives a copy of the chromosome(s) and sufficient monomers, and inorganic ions to begin life as an independent entity.
• Exponential growth is a repeated pattern where the number of cells doubles in a constant time interval.
• There are two broad classes of culture media: Defined media, which are prepared by adding precise amounts of pure inorganic or organic chemical to distilled water, and Complex media, which are made from digests of microbial, animal or plant products.
• The increase in cell number in an exponentially growing bacterial culture can be expressed mathematically as a geometric progression of the number 2.
• In the continuous culture growth vessel, a known volume of sterile medium is added at a constant rate while an equal volume of spent culture medium (which also contains cells) is removed at the same rate.
• Laboratory cultures of microorganisms are grown in culture media.
• Budding division is a process where the progeny develops from the generative tissue or cell of the parent organism.
• Stained samples are used to increase contrast between cells and their background.
• Generation time is when one cell eventually separates to form two cells, indicating that one generation has occurred.
• Microscopic counts can be performed either on samples dried on slide or on liquid samples.
• Growth is an increase in the number of cells.
• Biofilms are an attached polysaccharide matric containing embedded bacterial cells.
• Microscopic counting is a quick and easy way of estimating microbial cell numbers.
• As two cells become four, this is expressed as 2 1 – 2 2 and so on.
• During one generation, all cellular constituents increase proportionally.
• In order to control both specific growth rate and cell density independently, continuous culture, a type of an open system must be done.
• By measuring the rate of cell population increase over time, the growth depicts a certain ‘growth curve’.
• The most common type of continuous culture is the chemostat.
• The requirements for microbial growth can be divided into two main categories: physical and chemical.
• Physical requirements for microbial growth include temperature and pH.
• Most microorganisms grow well at the temperatures that humans favor, which are classified into three primary groups: Psychrophiles (cold-loving microbes) at 0 celsius, Mesophiles (moderate-temperature-loving microbes) between 25-40 celsius, and Thermophiles (heat-loving microbes) between 50-60 celsius.
• Hyperthermophiles have an optimum growth temperature of 80 celsius or higher.
• Extreme thermophiles grow at temperatures above 121 celsius.
• pH refers to the acidity or alkalinity of a solution.
• Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5.
• Very few bacteria grow at an acidic pH below about pH 4.
• Acidophiles are bacteria that love acidic environments.
• Microorganisms require water for growth, and their composition is 80-90% water.
• High osmotic pressures have the effect of removing necessary water from a cell.
• Hypertonic refers to a concentration of solutes that is higher than in the cell.
• Plasmolysis is the shrinkage of cell cytoplasm.
• Halophile are microorganisms that can grow in or tolerate saline conditions.
• Types of Halophile include Extreme Halophiles that require high salt concentration, Obligate Halophiles that require 30% of salt for growth, and Facultative Halophiles that require 15% of salt for growth.
• Carbon, Sulfur, Nitrogen, Phosphorus, Trace elements such as iron, copper, molybdenum, and zinc, Organic Growth Factors, and Oxygen are chemical requirements for microbial growth.
• Aerobes are microbes that use molecular oxygen.
• Anaerobes are microbes that do not use oxygen.