![]() 50 oC to 60 oC found in compost heaps and in boiling hot (base loving) exist from pH to 7.0 to 11.5 ex. Lactobacilllus (ferments milk)Įxist from pH to 5.4 to 8.5 most bacteria that cause human disease are in this category. Small quantities of nutrients, are diverse in their nutritional requirements. Ĭan exist in a great many environments because they are small, easily dispersed, need only a swimming pool, where small populations may go Of viable microbial cell in the volume of liquid that was filtered. The number of colonies that develop is the number Then theįilter is placed on an appropriate solid medium and incubated. The pores in the filter are too small for A known volume of liquid or air is drawn through a membrane filter by vacuum. Bacterial colonies are viewed through the magnifying glass against aĬolony-counting grid called a Quebec colony counter (we have this in the lab). The only particles present in the solution. Coulter Counter - electronic counter rapid & accurate only if bacterial cells are More accurate measurements of numbers of microbes. Methylene blue becomes colorless when reduced. Rate of utilization of a substrate, such as oxygen or glucose. Rate of formation of metabolic products, such as gases or acids, that a culture produces. Disadvantages: Not sensitive in terms of numbers of bacterialĬells & not useful for detecting minor contamination. Greater the mass of cells in the culture, the greater its turbidity (cloudiness) and the Spectrophotometer can measure how much light a solution of microbial cell transmits the Can hold tube up to the light and look for cloudiness as evidence of growth (measure a property of the mass of cells and then ESTIMATE the number of microbes) In the lab, we have to continually replace the Growth rate is set by the concentration of the scarcest or limiting nutrient, not by theĪccumulation of metabolic byproducts - in nature there is always some other microbe thatĬan use these metabolic byproducts for their own metabolism. Grow continually at a low but steady rate. Nutrients continuously enter the cell's environment at low concentrations, and populations In the lab, cultures usually pass throughĪll growth phases - not in nature. Not all cells necessarily die during this phase! Occurs because cell have depleted intracellular ATP reserves. (accumulation of metabolic byproducts, depletion of nutrients, etc.). The number of cells doesn't increase, but changes in cells occur: cell become smallerĪnd synthesize components to help them survive longer periods without growing (some mayĮven produce endospores) the signal to enter this phase may have to do with overcrowding Log growth for only a limited time, as nutrients are used up, metabolic wastes accumulate, Organisms in a tube of culture medium can maintain Increasing population increases slowly at first, then extremely rapidly. The number of microbes in an exponentially Generation time, the number of cells in the population increases by a factor of two). (logarithmic or exponential phase) - cell numbers increase exponentially during each (This phase may not occur, if theĬells used to inoculate a new culture are in the log phase & provided conditions are However, considerable metabolic activity is occurring as the cells prepare to grow. In the lag phase, the number of cells doesn't increase. That form the standard bacterial growth curve: (Not all Microbial lab culture typically passes through 4 distinct, sequential phases of growth (including yeasts) may also replicate by budding,įorming a bubble-like growth that enlarges and separates from the parent cell. The cell wall is laid down between them, producing two daughter cells.Ģ.) Budding - A few bacteria and some eukaryotes FollowingĭNA replication, the two chromosomes attach to separate sites on the plasma membrane, and Structures.] The bacterial cell doubles in Moving the chromosomes around during cell division (mitosis & meiosis) in mostĮukaryotic cells. [A spindle fiber apparatus made of protein filaments is responsible for Through fission, a primitive form of cellĭivision that does not employ a spindle fiberĪpparatus. Cell division leads to theġ.) Binary Fission - Bacterial reproduction occurs Population (or an increase in the number of cells), not to an increase in the size of the The term microbial growth refers to the growth of a
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