Growth of Bacterial Populations

The number of bacteria in a population, rather than the size of individual cells, is used to describe bacterial culture growth. A bacterial population grows in a geometric or exponential manner, with each division cycle (generation) producing 2 cells, 4 cells, 8 cells, 16 cells, 32 cells, and so on.

Many environmental factors, as well as the nature of the bacterial species, influence the generation period, which varies among bacteria. One of the fastest-growing bacteria, Clostridium perfringens, has an optimum generation time of about 10 minutes; Escherichia coli will double every 20 minutes, and the slow-growing Mycobacterium tuberculosis has a generation time of 12 to 16 hours. Certain bacteria populations living deep beneath the Earth's surface, according to some researchers, may develop at extremely slow rates, reproducing only once every several thousand years. The growth rate is heavily influenced by the composition of the growth medium. When the medium provides a stronger energy source and more of the biosynthetic intermediates that the cell would otherwise have to produce for itself, the growth rate reaches a limit.

The lag phase, the log phase, the stationary phase, and the death phase are the four stages of bacterial colony progress. Many environmental factors, as well as the nature of the bacterial species, influence the generation period, which varies among bacteria.

Log Phase

When bacteria are put in a medium that contains all of the nutrients they need for growth, they go through four stages of development that are characteristic of a bacterial growth curve. Bacteria do not replicate immediately after being inoculated into a new medium, and the population size remains constant. The cells are metabolically active and only grow in size during this period, known as the lag phase. Under their new environmental conditions, they're also synthesising the enzymes and factors needed for cell division and population development. The population then enters the log phase, in which cell numbers increase in a logarithmic fashion and each cell generation occurs at the same time interval as the one before it, resulting in a balanced increase in each cell's constituents. The log phase lasts until nutrients are exhausted or toxic products build up, at which point, cell growth slows and some cells start to die. Some bacterial species' maximum population at the end of the log process can reach a density of 10 to 30 billion cells per millilitre under ideal conditions.

Stationary Phase

The stationary phase of bacterial growth follows the log phase, in which the population size of bacteria remains constant, despite the fact that some cells continue to divide and others begin to die. The death process occurs after the stationary phase when the death of cells in the population outnumbers the development of new cells. The amount of time it takes for the death process to begin varies depending on the species and the medium. Bacteria do not always die when they are deprived of nutrients and can survive for long periods of time.

Ecology of Bacteria

Most people get confused between bacteria with disease-causing species, such as the Streptococcus bacteria, which were isolated from a man suffering from strep throat. Although pathogenic bacteria are responsible for diseases like cholera, tuberculosis, and gonorrhoea, they represent a tiny portion of the overall bacteria population.

Bacteria are so vast that only the broadest claims about their life history and ecology can be made. They can be found on the tops of mountains, at the bottom of the deepest seas, in animal guts, and even in Antarctica's frozen rocks and ice. Their ability to go dormant for long periods of time is one attribute that has enabled them to spread so far and last so long.

Factor Affecting Growth of Bacterial Populations

Bacterial growth is influenced by a variety of factors, including nutrient concentration and other environmental factors. The following are some of the most important factors that influence bacterial growth:

• Nutrition concentration

• Temperature

• Gaseous concentration

• pH

• Ions and salt concentration

• Available water

1. Nutrition Concentration

• Bacterial growth is enhanced when culture media contains a high concentration of growth-promoting substances. The rate of growth is slowed as nutrient concentration drops.

• The nutritional requirements of various bacteria vary.

2. Temperature

• Bacterial growth is influenced by temperature in a variety of ways.

• The minimum temperature is the lowest temperature that allows growth, and the maximum temperature is the highest temperature that allows growth.

• There is no growth below the minimum temperature and no growth above the maximum temperature.

• Since the cell membrane solidifies and stiffens below the minimum temperature required to transport nutrients into the cell, no growth occurs.

• Since cellular proteins and enzymes denature at high temperatures, bacterial growth is stopped.

3. pH

• Since pH affects the ionic properties of bacterial cells, it has an effect on bacterial growth.

• The majority of bacteria thrive at a neutral pH. Certain bacteria, on the other hand, thrive in an acidic or essential environment.

4. Ions and Salt

• Metal ions are needed for the production of enzymes and proteins by all bacteria.

• The majority of bacteria do not need NaCl in their media, but they can tolerate very low salt concentrations.

• Some halophilic bacteria, such as Archaebacteria, necessitate a high salt concentration in the media.

5. Gaseous Requirement

• Oxygen and carbon dioxide are two essential gases that influence bacterial growth.

• Aerobic respiration requires oxygen, and obligate aerobic bacteria must require oxygen to expand. Bacillus, Mycobacterium, etc.

• Oxygen is toxic or even fatal to obligate anaerobes. Facultative anaerobes, on the other hand, should withstand low oxygen concentrations.

• Capnophilic bacteria need carbon dioxide to survive. Campylobacter, Helicobacter pylori, and other bacteria. 

6.  Available Water

• The most important element for bacterial growth is water.

• The rate of metabolic and physiological activities of bacteria is determined by the amount of water available in the culture media.

• Water dissolves sugar, salts, and other chemicals, making them accessible to bacteria.

Growth of Bacterial Populations has a Wide Range of Environmental and Nutritive Requirements

Based on their reaction to gaseous oxygen, most bacteria can be classified into one of three classes. Aerobic bacteria flourish in the presence of oxygen and require it in order to develop and survive. Other bacteria, such as those found in deep marine sediments or those that cause bacterial food poisoning, are anaerobic and cannot tolerate gaseous oxygen. The facultative anaerobes are the third group, which tend to grow in the presence of oxygen but can also grow without it.

Bacteria can also be divided into groups based on how they get their energy. Bacteria are divided into two groups based on their energy source: heterotrophs and autotrophs. Heterotrophs get their energy from breaking down complex organic compounds that they must consume from the environment, such as saprobic bacteria contained in decaying matter, as well as bacteria that rely on fermentation or respiration.

The autotrophs, on the other hand, fix carbon dioxide to produce their own food, which can be fueled by light energy (photoautotrophic) or by the oxidation of nitrogen, sulphur, or other elements (chemoautotrophic). Photoautotrophs are more common than chemoautotrophs, and they are very diverse. Cyanobacteria, green sulphur bacteria, purple sulphur bacteria, and purple nonsulfur bacteria are some of them. The sulphur bacteria are particularly interesting because, unlike most other photosynthetic species, including cyanobacteria, they use hydrogen sulphide as a hydrogen donor rather than water.

Bacteria Play Important Roles in the Global Ecosystem

Bacterial activity is extremely important to the environment, both on land and in the water. Their constant labour completes the cycling of nutrients such as carbon, nitrogen, and sulphur. If it weren't for the operation of decomposers, the organic carbon in the form of dead and rotting organisms would rapidly deplete the carbon dioxide in the atmosphere. This may not seem like a huge deal to us, but consider that without carbon dioxide, plants will be unable to photosynthesise and produce food. When animals die, the carbon in their tissues is no longer accessible to any other living beings. One of the most essential functions of bacteria is decomposition, which involves the degradation of these species and the release of nutrients back into the atmosphere. Another essential function of bacteria is nitrogen cycling. Plants depend on nitrogen from the soil for their health and development, and they can't get it from the atmosphere's gaseous nitrogen. Nitrogen is primarily made accessible to them through the nitrogen fixation of bacteria like Rhizobium and cyanobacteria like Anabaena, Nostoc, and Spirulina. As part of their metabolism, these bacteria convert gaseous nitrogen to nitrates or nitrites, which are then released into the atmosphere. Some plants, such as liverworts, cycads, and legumes, have adapted their structures to house bacteria in their own tissues as a result of this process. Other denitrifying bacteria metabolise nitrates into nitrogen gas or nitrous oxide in the opposite direction. When these bacteria colonise cropland, they can deplete soil nutrients, making it difficult for crops to grow.

Importance of Growth of Bacterial Populations in Soil 

Soil bacteria are extremely active in causing biochemical changes in soil by converting different substances such as humus and minerals. Carbon, nitrogen, and sulphur, which are essential to life, are converted by bacteria from inorganic gaseous compounds into forms that plants and animals can use. Bacteria also transform plant and animal metabolism end products into forms that bacteria and other microorganisms may use. The nitrogen cycle can be used to demonstrate the role of bacteria in causing chemical changes. Nitrogen is found in nature as nitrate, nitrite, dinitrogen gas, some nitrogen oxides, ammonia, and organic amines in various oxidation states. The conversion of dinitrogen gas from the atmosphere into a form that can be used by living organisms is known as nitrogen fixation. Some nitrogen-fixing bacteria are free-living, such as Azotobacter, Clostridium pasteurianum, and Klebsiella pneumoniae, while Rhizobium species live in close proximity to leguminous plants.

Rhizobium species in the soil detect and invade their own plant host's root hairs, then penetrate the plant tissues and form a root nodule. Many of the bacteria's free-living characteristics are lost as a result of this process. They become reliant on the plant for carbon, and in exchange for carbon, they convert nitrogen gas to ammonia, which the plant uses for protein synthesis and growth. Furthermore, when nitrate is used as an electron acceptor, many bacteria may convert it to amines for the purpose of synthesising cellular materials or to ammonia. Nitrate is converted to dinitrogen gas by denitrifying bacteria. The aerobic species Nitrosomonas and Nitrobacter, which use ammonia as an electron donor, combine their activities to convert ammonia or organic amines to nitrate.

Importance of Growth of Bacterial Populations to Humans

Milk from a healthy cow produces very few bacteria at first, which come mainly from the cow's skin and milk handling procedures. Milk is an excellent growth medium for a variety of bacteria, and bacteria can multiply quickly if milk is not properly processed. If pathogenic bacteria are present, bacterial growth may ruin the milk or even pose a serious health risk. Milk is converted into useful dairy products such as buttermilk, yogurt, and cheese by a small number of bacteria. Buttermilk that has been commercially cultured is made from milk that has been inoculated with a Lactococcus starter culture. Yogurt and other fermented milk products are made in a similar way, but with different bacteria cultures. Bacteria also plays a role in the production of many kinds of cheese. Casein precipitates in milk, an acid-producing bacterium such as L. lactis grows to precipitate as curd. The curd is able to ripen by the action of other microorganisms after the moisture has been removed and salt has been added. The combination of Lactobacillus casei, Streptococcus thermophilus, and Propionibacterium shermanii is responsible for the ripening of Swiss cheese and the development of its characteristic taste and large gas bubbles. Moulds (Penicillium species) are used in the production of Roquefort and Camembert cheeses, and Brevibacterium linens are responsible for the flavour of Limburger cheese. Other bacteria have long been used in the preparation and preservation of foods made by bacterial fermentation, such as pickled products, sauerkraut, and olives.

Growth of Bacterial Populations in Industry

Various bacteria produce different end products as a result of anaerobic sugar fermentation reactions. The brewing industry has been using yeast to produce ethanol for thousands of years, and it is now used to make fuel. In the manufacture of vinegar, specific bacteria perform the oxidation of alcohol to acetic acid. Other fermentation methods produce far more valuable goods. Various Clostridium species produce organic compounds such as acetone, isopropanol, and butyric acid during fermentation, which can be prepared on an industrial scale. In extreme conditions, other bacterial products and reactions have been found. The enzymes isolated from thermophilic bacteria are of particular interest because they can carry out reactions at higher rates due to the higher temperatures at which they can occur.

Conclusion

Growth is described as an increase in the quantity of cellular constituents in a controlled manner. It is dependent on the cell's ability to generate new protoplasm from nutrients available in the environment. In most bacteria, growth entails an increase in cell mass and ribosome number, bacterial chromosome replication, synthesis of new cell walls and plasma membranes, chromosome partitioning, septum formation, and cell division.