Growth phase of microorganisms • Lag phaseis the adaptation phase, namely the phase of adjusting microorganisms to a new environment. The characteristic of the lag phase is that there is no increase in cell number, only an increase in cell size. The length of the lag phase depends on the initial conditions and number of microorganisms and the growth medium. • Log phaseis the phase in which microorganisms grow and divide at maximum speed, depending on the genetics of the microorganism, the nature of the medium, and the growth conditions. New cells are formed at a constant rate and their mass increases exponentially, which is why it is also called the log phaseExponential phase. • Stationary phaseis that the growth of microorganisms stops and a balance occurs between the cells that divide and the number of cells that die. In this phase, waste products accumulatetoxic. In most cases cell turnover occurs in the stationary phase. • Death phaseis a condition where the number of dead cells increases, and the causal factors are the unavailability of nutrients and the accumulation of toxic waste products. Measuring the growth of microorganisms. Growth of microorganisms cell concentration (number of cells per culture content) orcell density (dry weight of cells per unit of culture contents). These two parameters are not always the same because the average cell dry weight varies at different stages in culture growth. The growth of microorganisms can be measured in two ways, namely directly and indirectly. Direct measurement of the growth of microorganisms can be done in various ways: • Measurement using a counting chamber can be measured based on For this measurement, a counting booth is usedPetroff-Hausser, while for eukaryotic microorganisms hemocytometer measurements are used. The advantage of this method is that it is easy, cheap, fast, and provides information about the size and morphology of microorganisms. The disadvantage is that the population of microorganisms used must be large (minimum 106CFU per ml), because measurements with small volumes cannot differentiate between live and dead cells, and make it difficult to count motile cells. • Measurement via electronic counter In this measurement, a suspension of microorganisms is flowed through a small hole (orifice)with the help of electricity. Electrodes placed on two sides of the small hole measure the electrical resistance when the bacteria pass through the small hole, this is when the cells are counted.ProfitThis method produces faster and more accurate results, and can count cells in large sizes. The downsideis that this method cannot be used to count bacteria because there are disturbances in degris, filaments, and cannot differentiate between live cells and dead cells. • Measurement with plactingtechnique This method is a method for calculating the number of visible cells (fisible) and is based on the assumption that living bacteria will grow, divide, and produce a single colony. The unit of calculation used is CFU (colony forming unit) by making a sample dilution series and growing the sample on solid media. Measurements are carried out on plates with colony numbers ranging from 25-250 or 30-300.ProfitThis method is simple, easy and sensitive, because it uses a colony counter as a counting tool and can be used to count microorganisms in food, water or soil samples.The downsideis that appropriate media must be used and the calculations are less accurate because one colony does not always come from one individual cell.