Cycle of Growth
Binary fission is the mechanism by which one parent cell divides into two child cells and is how bacteria reproduce. Bacteria are considered to multiply exponentially (logarithmically) since one cell produces two offspring cells. The relationship below serves as an illustration of the idea of exponential growth:
Thus, after four generations, a single bacterium will yield sixteen bacteria.
For Escherichia coli, the doubling (generation) period can be as little as 20 minutes, but for Mycobacterium tuberculosis, it can take up to 18 hours. Numerous bacteria are produced quickly due to some species' low doubling times and exponential development. One E. Coli organism, for instance, may produce more than 1000 offspring in roughly three hours and more than one million in roughly seven hours. The amount of nutrients, temperature, pH, and other environmental variables all affect the doubling time in addition to the species.
There are four main stages in the bacterial growth cycle.
(1) The first is the lag phase, in which there is a lot of metabolic activity but no cell division.
This may continue for several hours or just a few minutes.
(2) Fast cell division takes place during the log (logarithmic) phase. Penicillin and other β-lactam medications work during this stage because they are active when cells are dividing and producing peptidoglycan. The exponential phase is another name for the log phase.
(3) The stationary phase is the period after poisonous substances or nutrient depletion slow down growth until the number of newly formed cells equals the number of dying cells, creating a steady state. cells cultured in a unique device known as a "chemostat," to which new nutrients are introduced and from which waste products are continuously eliminated, can continue to exist in the log phase and avoid going into the stationary phase.
(4) The last stage, known as the death phase, is identified by a drop in the quantity of live bacteria.
Aerobic and anaerobic expansion
A sufficient amount of oxygen improves metabolism and growth for the majority of species. During the final stages of energy production, which are catalyzed by flavoproteins and cytochromes, oxygen serves as the hydrogen acceptor. Bacteria need two enzymes to consume oxygen because it produces two harmful chemicals when it does so: hydrogen peroxide (H2O2) and the free radical superoxide (O2). Superoxide dismutase is the first, and it catalyzes the reaction.
The ability of bacteria to respond to oxygen is a crucial classification criterion that has significant applications since patient specimens need to be incubated in the right environment for the bacteria to proliferate.
(1) Certain bacteria, including M. tuberculosis, are obligate aerobes, meaning they need oxygen to grow because oxygen is a necessary hydrogen acceptor for their ATP-generating machinery.
(2) Some bacteria, like E. Coli, are facultative anaerobes; in the presence of oxygen, they use it to produce energy through respiration; in the absence of oxygen, they can manufacture ATP through the fermentation pathway.
(3) Obedient anaerobes, like Clostridium tetani, belong to the third category of bacteria. They are unable to proliferate in the presence of oxygen due to the absence of either catalase or superoxide dismutase, or both.
The way that obligatory anaerobes react to oxygen exposure varies; although some can live and thrive, others perish quickly.
SUGAR FERMENTATION
Several significant human infections are identified in clinical laboratories via the fermentation of certain sugars. For instance, the fermentation of either glucose or maltose can be used to identify Neisseria gonorrhoeae and Neisseria meningitidis from one another, and the fermentation of lactose can be used to distinguish E. coli from Salmonella and Shigella.
The breakdown of sugar (such as glucose or maltose) into pyruvic acid and subsequently, lactic acid is referred to as fermentation. To be more precise, it is the disintegration of a monosaccharide like galactose, maltose, or glucose.
The pyruvate produced by fermentation enters the Krebs cycle (oxidation cycle, tricarboxylic acid cycle) if oxygen is present, where it is digested to produce CO2 and H2O as the end products. Because the Krebs cycle produces a lot more ATP than the glycolytic cycle, facultative bacteria proliferate more quickly when oxygen is present. Aerobes, which can only thrive in the presence of oxygen, do not ferment; facultative and anaerobic bacteria do. Pseudomonas aeruginosa and other aerobes create metabolites through non-fermentation mechanisms such as amino acid deamination that enter the Krebs cycle.
In clinical laboratory fermentation tests, the medium becomes acidic due to the generation of lactate and pyruvate. This is indicated by a pH indicator that changes color in response to pH variations.
IRON METABOLISM
Bacteria need iron, in the form of ferric ions, to develop since it is a necessary component of cytochromes and other enzymes. Because iron is bound to iron-binding proteins like transferrin, there is very little iron available for pathogenic microorganisms in the human body. Bacteria manufacture siderophores, which are iron-binding chemicals, to obtain iron for their growth. Siderophores, like the enterobactin that E. coli produces, are secreted by the bacteria, which chelate iron to make it available for usage inside the cell by attaching to certain receptors on the bacterial surface.
While eukaryotic cells reproduce by mitosis, bacteria replicate via binary fission.
• There are four stages in the bacterial growth cycle: the lag phase, when nutrients are incorporated; the log phase, when cell division happens quickly; the stationary phase, when the number of dying cells equals the number of newly formed cells; and the death phase, when the majority of cells die due to nutrient exhaustion.
Aerobes and facultatives are two types of bacteria that can thrive in the presence of oxygen, whereas anaerobes are bacteria that perish in the presence of oxygen. When bacteria consume oxygen, harmful byproducts like hydrogen peroxide and superoxide are produced. Superoxide dismutase and catalase are two examples of the enzymes found in facultative and aerobes that help them detoxify these compounds; anaerobes cannot accomplish this and are destroyed.
• The basis for identifying several significant infections in a lab setting is the fermentation of specific carbohydrates. When carbohydrates like glucose ferment, pyruvic acid or lactic acid are produced along with ATP. The indicator dyes' altered color indicates that these acids are lowering the pH.
CHANGES
A mutation is a change in the DNA's base sequence that typically causes a protein to assemble with a different amino acid and exhibit a different phenotype. Three different types of molecular alterations cause mutations:
Base substitution is the first kind. When one base is put in lieu of another, something happens. It occurs during DNA replication for one of two reasons: either the DNA polymerase makes a mistake or because a mutagen causes the base being used as a template's hydrogen bonding to change in a way that causes the incorrect base to be inserted. A base substitution is referred to as a missense mutation if it produces a codon that only inserts a different amino acid; a nonsense mutation is produced when the substitution results in a termination codon that prematurely ends protein production. Protein function is nearly always destroyed by nonsense mutations.
(2) Frameshift mutations are the second kind of mutations. This happens when one or more base pairs are added or removed, shifting the ribosome's reading frame and causing the incorrect amino acids to be incorporated "downstream" from the mutation and in the creation of a protein that isn't active.
(3) The integration of transposons or insertion sequences into the DNA results in the third kind of mutation. These recently inserted DNA fragments have the power to significantly alter neighboring genes as well as the genes they insert.
Radiation, chemicals, and viruses can all result in mutations. Chemicals have a variety of actions.
Certain substances, such as alkylating agents and nitrous acid, change the base that already exists so that it preferentially forms a hydrogen bond with the incorrect base (for example, adenine would now couple with cytosine rather than thymine).
Certain substances, including 5-bromouracil, are analogs of bases because they share similarities with typical bases.
5-bromouracil can be added because the atomic radius of the bromine atom is comparable to that of a methyl group.
(3) Certain substances, like tobacco smoke's benzpyrene, attach to the DNA bases already present and result in frameshift mutations. These substances intercalate between the neighboring bases, twisting and offsetting the DNA sequence. They are often both carcinogens and mutagens.
Mutations can also be brought on by UV radiation and X-rays.
(1) High-energy X-rays can harm DNA in three ways: (a) by rupturing the covalent bonds that bind the ribose phosphate chain; (b) by generating free radicals that can attack the bases; and (c) by modifying the bases' electron composition, which modifies their hydrogen bonding.
Subsequent to the energy difference between ultraviolet and X-rays, the cross-linking of neighboring pyrimidine bases results in the formation of dimers. When adjacent thymines cross-link to form a thymine dimer, for example, the DNA is unable to replicate correctly.
When the DNA of some viruses is introduced into a bacterial chromosome, it frequently causes changes, such as the mutator bacteriophage Mu. Gene mutations can happen because the viral DNA might insert into a variety of locations. These changes are either deletions or frameshift mutations.
