What is the difference between lag phase and log phase

It has been determined that in a closed system or batch culture no food added, no wastes removed bacteria will grow in a predictable pattern, resulting in a growth curve composed of four distinct phases of growth: the lag phase, the exponential or log phase, the stationary phase, and the death or decline phase.

Additionally, this growth curve can yield generation time for a particular organism — the amount of time it takes for the population to double. Bacterial Growth Curve. For more information, write to my e-mail address: m. The details associated with each growth curve number of cells, length of each phase, rapidness of growth or death, overall amount of time will vary from organism to organism or even with different conditions for the same organism.

But the pattern of four distinct phases of growth will typically remain. The lag phase is an adaptation period, where the bacteria are adjusting to their new conditions. The length of the lag phase can vary considerably, based on how different the conditions are from the conditions that the bacteria came from, as well as the condition of the bacterial cells themselves.

Actively growing cells transferred from one type of media into the same type of media, with the same environmental conditions, will have the shortest lag period. Damaged cells will have a long lag period, since they must repair themselves before they can engage in reproduction.

Typically cells in the lag period are synthesizing RNA, enzymes, and essential metabolites that might be missing from their new environment such as growth factors or macromolecules , as well as adjusting to environmental changes such as changes in temperature, pH, or oxygen availability. They can also be undertaking any necessary repair of injured cells.

Once cells have accumulated all that they need for growth, they proceed into cell division. The exponential or log phase of growth is marked by predictable doublings of the population, where 1 cell become 2 cells, becomes 4, becomes 8 etc. Conditions that are optimal for the cells will result in very rapid growth and a steeper slope on the growth curve , while less than ideal conditions will result in slower growth. Cells in the exponential phase of growth are the healthiest and most uniform, which explains why most experiments utilize cells from this phase.

Due to the predictability of growth in this phase, this phase can be used to mathematically calculate the time it takes for the bacterial population to double in number, known as the generation time g. This information is used by microbiologists in basic research, as well as in industry. In order to determine generation time, the natural logarithm of cell number can be plotted against time where the units can vary, depending upon speed of growth for the particular population , using a semilogarithmic graph to generate a line with a predictable slope.

The slope of the line is equal to 0. Alternatively one can rely on the fixed relationship between the initial number of cells at the start of the exponential phase and the number of cells after some period of time, which can be expressed by:. Thus, if one knows the cell concentration at the start of the exponential phase of growth and the cell concentration after some period of time of exponential growth, the number of generations can be calculated. Then, using the amount of time that growth was allowed to proceed t , one can calculate g.

All good things must come to an end otherwise bacteria would equal the mass of the Earth in 7 days! As environmental conditions change and become the limiting factor in growth, cells slow reproduction and enter a stationary phase. In this stage cells are technically still reproducing but it is less than before and roughly equal to the amount of cell death.

The stationary phase is when conditions are no longer ideal for reproduction and cells start to experience stress that results in changed metabolic activity. Depending on the type of cell being grown, this may be the stage where protein production and excretion takes place or where spore forming bacteria start to produce endospores allowing them to survive harsh conditions.

During the stationary phase of cell culture, it is generally considered to be the products of the cells that are of interest and that makes this an important part of bioprocessing. Additional supplements may be added to keep the cells alive but stressed enough to continue producing rather than reproducing.

In cases where cell culture may last days, weeks, or months, like the production of monoclonal antibodies via hybridoma cells, or the production of ethanol and CO 2 via yeast fermentation, the stationary phase is where the magic happens.

As waste builds up and nutrient rich media is depleted, the death phase is the point where the living cells stop metabolic functions and begin the process of death. As cells lyse and fill the culture with what was once on their insides, the environment changes one last time and exponential decay begins. This is true in cases where cells lyse and release amino acids, proteins, polysaccharides, and free fatty acids that may be the intended products.

Food sciences are especially affected by the death phase in cell culture and will often control the exact time it begins by altering environmental conditions to stop metabolic cellular activity. Create an Account. Necessary cookies are absolutely essential for the website to function properly.

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Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. Following DNA replication, the two chromosomes attach to separate sites on the plasma membrane, and the cell wall is laid down between them, producing two daughter cells.

Budding - A few bacteria and some eukaryotes including yeasts may also replicate by budding , forming a bubble-like growth that enlarges and separates from the parent cell. Microbial Growth. Phases of Growth - A microbial lab culture typically passes through 4 distinct, sequential phases of growth that form the standard bacterial growth curve : Not all growth phases occur in all cultures. Lag Phase - In the lag phase, the number of cells doesn't increase.

However, considerable metabolic activity is occurring as the cells prepare to grow. Log Phase logarithmic or exponential phase - cell numbers increase exponentially; during each generation time, the number of cells in the population increases by a factor of two. The number of microbes in an exponentially increasing population increases slowly at first, then extremely rapidly.

Organisms in a tube of culture medium can maintain log growth for only a limited time, as nutrients are used up, metabolic wastes accumulate, microobes suffer from oxygen depletion. Stationary Phase - The number of cells doesn't increase, but changes in cells occur: cell become smaller and synthesize components to help them survive longer periods without growing some may even produce endospores ; the signal to enter this phase may have to do with overcrowding accumulation of metabolic byproducts, depletion of nutrients, etc.

Death Phase - In this phase, cells begin to die out. Death occurs exponentially, but at a low rate. Death occurs because cell have depleted intracellular ATP reserves. Not all cells necessarily die during this phase! In the lab, cultures usually pass through all growth phases - not in nature. In nature, nutrients continuously enter the cell's environment at low concentrations, and populations grow continually at a low but steady rate.

The growth rate is set by the concentration of the scarcest or limiting nutrient, not by the accumulation of metabolic byproducts - in nature there is always some other microbe that can use these metabolic byproducts for their own metabolism. In the lab, we have to continually replace the media. A spectrophotometer can measure how much light a solution of microbial cell transmits; the greater the mass of cells in the culture, the greater its turbidity cloudiness and the less light that will be transmitted.

Metabolic Activity - 3 ways:. The rate of formation of metabolic products, such as gases or acids, that a culture produces. The rate of utilization of a substrate, such as oxygen or glucose. The rate of reduction of certain dyes. Direct Measurements - Give more accurate measurements of numbers of microbes.