Bacterial growth

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Growth is shown as L = log(numbers) where numbers is the number of colony forming units per ml, versus T (time.) Bacterial growth.png
Growth is shown as L = log(numbers) where numbers is the number of colony forming units per ml, versus T (time.)

Bacterial growth is proliferation of bacterium into two daughter cells, in a process called binary fission. Providing no mutation event occurs, the resulting daughter cells are genetically identical to the original cell. Hence, bacterial growth occurs. Both daughter cells from the division do not necessarily survive. However, if the surviving number exceeds unity on average, the bacterial population undergoes exponential growth. The measurement of an exponential bacterial growth curve in batch culture was traditionally a part of the training of all microbiologists; the basic means requires bacterial enumeration (cell counting) by direct and individual (microscopic, flow cytometry [1] ), direct and bulk (biomass), indirect and individual (colony counting), or indirect and bulk (most probable number, turbidity, nutrient uptake) methods. Models reconcile theory with the measurements. [2]

Contents

Phases

Bacterial growth curve\Kinetic Curve Bacterial growth en.svg
Bacterial growth curve\Kinetic Curve

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). [3]

  1. During lag phase, bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are maturing and not yet able to divide. During the lag phase of the bacterial growth cycle, the synthesis of RNA, enzymes and other molecules occurs. During the lag phase cells change very little because the cells do not immediately reproduce in a new medium. This period of little to no cell division is called the lag phase and can last for 1 hour to several days. During this phase cells are not dormant. [4]
  2. The log phase (sometimes called the logarithmic phase or the exponential phase) is a period characterized by cell doubling. [5] The number of new bacteria appearing per unit time is proportional to the present population. If growth is not limited, doubling will continue at a constant rate so both the number of cells and the rate of population increase doubles with each consecutive time period. For this type of exponential growth, plotting the natural logarithm of cell number against time produces a straight line. The slope of this line is the specific growth rate of the organism, which is a measure of the number of divisions per cell per unit time. [5] The actual rate of this growth (i.e. the slope of the line in the figure) depends upon the growth conditions, which affect the frequency of cell division events and the probability of both daughter cells surviving. Under controlled conditions, cyanobacteria can double their population four times a day and then they can triple their population. [6] Exponential growth cannot continue indefinitely, however, because the medium is soon depleted of nutrients and enriched with wastes.
  3. The stationary phase is often due to a growth-limiting factor such as the depletion of an essential nutrient, and/or the formation of an inhibitory product such as an organic acid. Stationary phase results from a situation in which growth rate and death rate are equal. The number of new cells created is limited by the growth factor and as a result the rate of cell growth matches the rate of cell death. The result is a “smooth,” horizontal linear part of the curve during the stationary phase. Mutations can occur during stationary phase. Bridges et al. (2001) [7] presented evidence that DNA damage is responsible for many of the mutations arising in the genomes of stationary phase or starving bacteria. Endogenously generated reactive oxygen species appear to be a major source of such damages. [7] Bacteria in this phase sometimes enter dormancy, using hibernation factors to slow their metabolism. [8]
  4. At death phase (decline phase), bacteria die. This could be caused by lack of nutrients, environmental temperature above or below the tolerance band for the species, or other injurious conditions.

This basic batch culture growth model draws out and emphasizes aspects of bacterial growth which may differ from the growth of macrofauna. It emphasizes clonality, asexual binary division, the short development time relative to replication itself, the seemingly low death rate, the need to move from a dormant state to a reproductive state or to condition the media, and finally, the tendency of lab adapted strains to exhaust their nutrients. In reality, even in batch culture, the four phases are not well defined. The cells do not reproduce in synchrony without explicit and continual prompting (as in experiments with stalked bacteria [9] ) and their exponential phase growth is often not ever a constant rate, but instead a slowly decaying rate, a constant stochastic response to pressures both to reproduce and to go dormant in the face of declining nutrient concentrations and increasing waste concentrations.

The decrease in number of bacteria may even become logarithmic. Hence, this phase of growth may also be called as negative logarithmic or negative exponential growth phase.

Near the end of the logarithmic phase of a batch culture, competence for natural genetic transformation may be induced, as in Bacillus subtilis [10] and in other bacteria. Natural genetic transformation is a form of DNA transfer that appears to be an adaptation for repairing DNA damages.

Batch culture is the most common laboratory growth method in which bacterial growth is studied, but it is only one of many. It is ideally spatially unstructured and temporally structured. The bacterial culture is incubated in a closed vessel with a single batch of medium. In some experimental regimes, some of the bacterial culture is periodically removed and added to fresh sterile medium. In the extreme case, this leads to the continual renewal of the nutrients. This is a chemostat, also known as continuous culture. It is ideally spatially unstructured and temporally unstructured, in a steady state defined by the rates of nutrient supply and bacterial growth. In comparison to batch culture, bacteria are maintained in exponential growth phase, and the growth rate of the bacteria is known. Related devices include turbidostats and auxostats. When Escherichia coli is growing very slowly with a doubling time of 16 hours in a chemostat most cells have a single chromosome. [1]

Bacterial growth can be suppressed with bacteriostats, without necessarily killing the bacteria. Certain toxins can be used to suppress bacterial growth or kill bacteria. Antibiotics (or, more properly, antibacterial drugs) are drugs used to kill bacteria; they can have side effects or even cause adverse reactions in people, however they are not classified as toxins. In a synecological, true-to-nature situation in which more than one bacterial species is present, the growth of microbes is more dynamic and continual.

Liquid is not the only laboratory environment for bacterial growth. Spatially structured environments such as biofilms or agar surfaces present additional complex growth models.

The 5th phase: Long-term stationary phase

Long-term stationary phase, unlike early stationary phase (in which there is little cell division), is a highly dynamic period in which the birth and death rates are balanced. It's been proven that after death phase E. coli can be maintained in batch culture for long periods without adding nutrients. [11] [12] By providing sterile distilled water to maintain volume and osmolarity, aerobically grown cultures can be maintained at densities of ~106 colony-forming units (CFUs) per ml for more than 5 years without the addition of nutrients in batch culture. [13]

Environmental conditions

Environmental factors influence rate of bacterial growth such as acidity (pH), temperature, water activity, macro and micro nutrients, oxygen levels, and toxins. Conditions tend to be relatively consistent between bacteria with the exception of extremophiles. Bacterium have optimal growth conditions under which they thrive, but once outside of those conditions the stress can result in either reduced or stalled growth, dormancy (such as formation spores), or death. Maintaining sub-optimal growth conditions is a key principle to food preservation.

Temperature

Low temperatures tend to reduce growth rates which has led to refrigeration being instrumental in food preservation. Depending on temperature, bacteria can be classified as:

Psychrophiles are extremophilic cold-loving bacteria or archaea with an optimal temperature for growth at about 15 °C or lower (maximal temperature for growth at 20 °C, minimal temperature for growth at 0 °C or lower). Psychrophiles are typically found in Earth's extremely cold ecosystems, such as polar ice-cap regions, permafrost, polar surface, and deep oceans. [14]

Mesophiles are bacteria that thrive at moderate temperatures, growing best between 20° and 45 °C. These temperatures align with the natural body temperatures of humans, which is why many human pathogens are mesophiles. [15]

Survive under temperatures of 45–80 °C. [16]

Acidity

Optimal acidity for bacteria tends to be around pH 6.5 to 7.0 with the exception of acidophiles. Some bacteria can change the pH such as by excreting acid resulting in sub-optimal conditions. [17]

Water activity

Oxygen

Bacteria can be aerobes or anaerobes. Depending on the degree of oxygen required bacteria can fall into the following classes:

  1. facultative-anaerobes-ie aerotolerant absence or minimal oxygen required for their growth
  2. obligate-anaerobes grow only in complete absence of oxygen
  3. facultative aerobes-can grow either in presence or minimal oxygen
  4. obligate aerobes-grow only in the presence of oxygen

Micronutrients

Ample nutrients

Toxic compounds

Toxic compounds such as ethanol can hinder growth or kill bacteria. This is used beneficially for disinfection and in food preservation.

See also

Related Research Articles

<span class="mw-page-title-main">Thermophile</span> Organism that thrives at relatively high temperatures

A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between 41 and 122 °C. Many thermophiles are archaea, though some of them are bacteria and fungi. Thermophilic eubacteria are suggested to have been among the earliest bacteria.

<span class="mw-page-title-main">Endospore</span> Protective structure formed by bacteria

An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form, but it is not a true spore. It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in gram-positive bacteria. In endospore formation, the bacterium divides within its cell wall, and one side then engulfs the other. Endospores enable bacteria to lie dormant for extended periods, even centuries. There are many reports of spores remaining viable over 10,000 years, and revival of spores millions of years old has been claimed. There is one report of viable spores of Bacillus marismortui in salt crystals approximately 25 million years old. When the environment becomes more favorable, the endospore can reactivate itself into a vegetative state. Most types of bacteria cannot change to the endospore form. Examples of bacterial species that can form endospores include Bacillus cereus, Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, and Clostridium tetani. Endospore formation is not found among Archaea.

A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from 20 to 45 °C. The optimum growth temperature for these organisms is 37 °C. The term is mainly applied to microorganisms. Organisms that prefer extreme environments are known as extremophiles. Mesophiles have diverse classifications, belonging to two domains: Bacteria, Archaea, and to kingdom Fungi of domain Eucarya. Mesophiles belonging to the domain Bacteria can either be gram-positive or gram-negative. Oxygen requirements for mesophiles can be aerobic or anaerobic. There are three basic shapes of mesophiles: coccus, bacillus, and spiral.

<span class="mw-page-title-main">Microbiological culture</span> Method of allowing microorganisms to multiply in a controlled medium

A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagnostic methods used as research tools in molecular biology.

<span class="mw-page-title-main">Psychrophile</span> Organism capable of growing and reproducing in the cold

Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C (−4 °F) to 20 °C (68 °F). They are found in places that are permanently cold, such as the polar regions and the deep sea. They can be contrasted with thermophiles, which are organisms that thrive at unusually high temperatures, and mesophiles at intermediate temperatures. Psychrophile is Greek for 'cold-loving', from Ancient Greek ψυχρός (psukhrós) 'cold, frozen'.

<span class="mw-page-title-main">Subculture (biology)</span>

In biology, a subculture is either a new cell culture or a microbiological culture made by transferring some or all cells from a previous culture to fresh growth medium. This action is called subculturing or passaging the cells. Subculturing is used to prolong the lifespan and/or increase the number of cells or microorganisms in the culture.

Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity chemicals, such as acetic acid, citric acid, and ethanol are made by fermentation. Moreover, nearly all commercially produced industrial enzymes, such as lipase, invertase and rennet, are made by fermentation with genetically modified microbes. In some cases, production of biomass itself is the objective, as is the case for single-cell proteins, baker's yeast, and starter cultures for lactic acid bacteria used in cheesemaking.

<span class="mw-page-title-main">Chemostat</span> A type of bioreactor

A chemostat is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms is continuously removed at the same rate to keep the culture volume constant. By changing the rate with which medium is added to the bioreactor the specific growth rate of the microorganism can be easily controlled within limits.

The gene rpoS encodes the sigma factor sigma-38, a 37.8 kD protein in Escherichia coli. Sigma factors are proteins that regulate transcription in bacteria. Sigma factors can be activated in response to different environmental conditions. rpoS is transcribed in late exponential phase, and RpoS is the primary regulator of stationary phase genes. RpoS is a central regulator of the general stress response and operates in both a retroactive and a proactive manner: it not only allows the cell to survive environmental challenges, but it also prepares the cell for subsequent stresses (cross-protection). The transcriptional regulator CsgD is central to biofilm formation, controlling the expression of the curli structural and export proteins, and the diguanylate cyclase, adrA, which indirectly activates cellulose production. The rpoS gene most likely originated in the gammaproteobacteria.

<span class="mw-page-title-main">Bacteria</span> Domain of microorganisms

Bacteria are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit the air, soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

A copiotroph is an organism found in environments rich in nutrients, particularly carbon. They are the opposite to oligotrophs, which survive in much lower carbon concentrations.

Fed-batch culture is, in the broadest sense, defined as an operational technique in biotechnological processes where one or more nutrients (substrates) are fed (supplied) to the bioreactor during cultivation and in which the product(s) remain in the bioreactor until the end of the run. An alternative description of the method is that of a culture in which "a base medium supports initial cell culture and a feed medium is added to prevent nutrient depletion". It is also a type of semi-batch culture. In some cases, all the nutrients are fed into the bioreactor. The advantage of the fed-batch culture is that one can control concentration of fed-substrate in the culture liquid at arbitrarily desired levels.

<span class="mw-page-title-main">Microbial cyst</span> Resting or dormant stage of a microorganism

A microbial cyst is a resting or dormant stage of a microorganism, that can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion. Many groups of single-celled, microscopic organisms, or microbes, possess the ability to enter this dormant state.

Diauxic growth, diauxie or diphasic growth is any cell growth characterized by cellular growth in two phases. Diauxic growth, meaning double growth, is caused by the presence of two sugars on a culture growth media, one of which is easier for the target bacterium to metabolize. The preferred sugar is consumed first, which leads to rapid growth, followed by a lag phase. During the lag phase the cellular machinery used to metabolize the second sugar is activated and subsequently the second sugar is metabolized.

Bacterial morphological plasticity refers to changes in the shape and size that bacterial cells undergo when they encounter stressful environments. Although bacteria have evolved complex molecular strategies to maintain their shape, many are able to alter their shape as a survival strategy in response to protist predators, antibiotics, the immune response, and other threats.

Deinococcus frigens is a species of low temperature and drought-tolerating, UV-resistant bacteria from Antarctica. It is Gram-positive, non-motile and coccoid-shaped. Its type strain is AA-692. Individual Deinococcus frigens range in size from 0.9-2.0 μm and colonies appear orange or pink in color. Liquid-grown cells viewed using phase-contrast light microscopy and transmission electron microscopy on agar-coated slides show that isolated D. frigens appear to produce buds. Comparison of the genomes of Deiococcus radiodurans and D. frigens have predicted that no flagellar assembly exists in D. frigens.

Diagnostic microbiology is the study of microbial identification. Since the discovery of the germ theory of disease, scientists have been finding ways to harvest specific organisms. Using methods such as differential media or genome sequencing, physicians and scientists can observe novel functions in organisms for more effective and accurate diagnosis of organisms. Methods used in diagnostic microbiology are often used to take advantage of a particular difference in organisms and attain information about what species it can be identified as, which is often through a reference of previous studies. New studies provide information that others can reference so that scientists can attain a basic understanding of the organism they are examining.

<span class="mw-page-title-main">Sea ice microbial communities</span> Groups of microorganisms living within and at the interfaces of sea ice

Sea Ice Microbial Communities (SIMCO) refer to groups of microorganisms living within and at the interfaces of sea ice at the poles. The ice matrix they inhabit has strong vertical gradients of salinity, light, temperature and nutrients. Sea ice chemistry is most influenced by the salinity of the brine which affects the pH and the concentration of dissolved nutrients and gases. The brine formed during the melting sea ice creates pores and channels in the sea ice in which these microbes can live. As a result of these gradients and dynamic conditions, a higher abundance of microbes are found in the lower layer of the ice, although some are found in the middle and upper layers. Despite this extreme variability in environmental conditions, the taxonomical community composition tends to remain consistent throughout the year, until the ice melts.

TM7x, also known as Nanosynbacter lyticus type strain TM7x HMT 952. is a phylotype of one of the most enigmatic phyla, Candidatus Saccharibacteria, formerly candidate phylum TM7. It is the only member of the candidate phylum that has been cultivated successfully from the human oral cavity, and stably maintained in vitro. and serves as a crucial paradigm. of the newly described Candidate Phyla Radiation (CPR). The cultivated oral taxon is designated as Saccharibacteria oral taxon TM7x. TM7x has a unique lifestyle in comparison to other bacteria that are associated with humans. It is an obligate epibiont parasite, or an "epiparasite", growing on the surface of its host bacterial species Actinomyces odontolyticus subspecies actinosynbacter strain XH001, which is referred to as the "basibiont". Actinomyces species are one of the early microbial colonizers in the oral cavity. Together, they exhibit parasitic epibiont symbiosis.

Saprotrophic bacteria are bacteria that are typically soil-dwelling and utilize saprotrophic nutrition as their primary energy source. They are often associated with soil fungi that also use saprotrophic nutrition and both are classified as saprotrophs.

References

  1. 1 2 Skarstad K, Steen HB, Boye E (1983). "Cell cycle parameters of slowly growing Escherichia coli B/r studied by flow cytometry". J. Bacteriol. 154 (2): 656–62. doi:10.1128/jb.154.2.656-662.1983. PMC   217513 . PMID   6341358.
  2. ↑ Zwietering MH, Jongenburger I, Rombouts FM, van 'T Riet K (1990). "Modeling of the Bacterial Growth Curve". Applied and Environmental Microbiology. 56 (6): 1875–1881. Bibcode:1990ApEnM..56.1875Z. doi:10.1128/aem.56.6.1875-1881.1990. PMC   184525 . PMID   16348228.
  3. ↑ Fankhauser DB (July 17, 2004). "Bacterial Growth Curve". University of Cincinnati Clermont College. Archived from the original on February 13, 2016. Retrieved December 29, 2015.
  4. ↑ Case C, Funke B, Tortora G (2010). Microbiology An Introduction (Tenth ed.). ISBN   978-0-321-55007-1.
  5. 1 2 "Bacterial Growth". BACANOVA project. European Commission. Archived from the original on October 24, 2007. Retrieved May 7, 2008.
  6. ↑ Coutts DA (December 15, 2011). "Marshall T. Savage - An Exponentialist View". Famous Exponentialists. Exponentialist homepage.
  7. 1 2 Bridges BA, Foster PL, Timms AR (2001). "Effect of endogenous carotenoids on "adaptive" mutation in Escherichia coli FC40". Mutat. Res. 473 (1): 109–19. doi:10.1016/s0027-5107(00)00144-5. PMC   2929247 . PMID   11166030.
  8. ↑ Samorodnitsky, Dan (June 5, 2024). "Most Life on Earth is Dormant, After Pulling an 'Emergency Brake'". Quanta Magazine. Retrieved June 12, 2024.
  9. ↑ Novick A (1955). "Growth of Bacteria". Annual Review of Microbiology. 9: 97–110. doi:10.1146/annurev.mi.09.100155.000525. PMID   13259461.
  10. ↑ Anagnostopoulos C, Spizizen J (1961). "Requirements for Transformation in Bacillus Subtilis". J. Bacteriol. 81 (5): 741–6. doi:10.1128/JB.81.5.741-746.1961. PMC   279084 . PMID   16561900.
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  12. ↑ Finkel SE, Kolter R (March 1999). "Evolution of microbial diversity during prolonged starvation". Proceedings of the National Academy of Sciences of the United States of America. 96 (7): 4023–4027. Bibcode:1999PNAS...96.4023F. doi: 10.1073/pnas.96.7.4023 . PMC   22413 . PMID   10097156.
  13. ↑ Finkel SE (February 2006). "Long-term survival during stationary phase: evolution and the GASP phenotype". Nature Reviews. Microbiology. 4 (2): 113–120. doi:10.1038/nrmicro1340. PMID   16415927. S2CID   3337959.
  14. ↑ Moyer CL, Morita RY (April 16, 2007). "Psychrophiles and Psychrotrophs". eLS. doi:10.1002/9780470015902.a0000402.pub2. ISBN   9780470016176.
  15. ↑ "Mesophile". Biology-Online Dictionary. Retrieved February 6, 2018.
  16. ↑ Bergey DH (July 1919). "Thermophilic Bacteria". Journal of Bacteriology. 4 (4): 301–306. doi:10.1128/jb.4.4.301-306.1919. PMC   378811 . PMID   16558843.
  17. ↑ Blamire J. "Effect of pH on Growth Rate". Brooklyn College. Retrieved October 8, 2016.

This article includes material from an article posted on 26 April 2003 on Nupedia; written by Nagina Parmar; reviewed and approved by the Biology group; editor, Gaytha Langlois; lead reviewer, Gaytha Langlois; lead copyeditors, Ruth Ifcher. and Jan Hogle.

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