Unicellular organisms are capable of autonomous existence and carrying out life’s primary duties. A cell’s structure must be complete for it to live independently. As a result, all living things’ cells are the primary structural and functional unit.
Under the microscope, you’ve seen cells in an onion peel and human cheek cells before. The outer membrane of the human cheek cell serves as the cell’s delimiting structure. The nucleus is a compact membrane-bound structure found inside each cell. The chromosomes, which carry the genetic material, are housed in this nucleus.
Structure of bacterium
Bacteria are all one-celled organisms. All cells are prokaryotic. They don’t have a nucleus or any membrane-enclosed structures. A light microscope may observe giant bacterial cells, but an electron microscope is required.
Bacteria are prokaryotic bacteria with just one cell. They are devoid of a nuclear membrane. Double-stranded circular DNA makes up the nucleus of a bacterium. Polysaccharides, which are found in specific structures of a bacterium, make up most of the DNA.
The structure of a bacterium has a stiff exterior coating called the cell wall. The capsule is the cell wall’s outer coating. Peptidoglycan is the main component. Microorganisms are a distinct form: cytoplasmic membrane, mesosomes, ribosomes, and cytoplasmic inclusions.
Bacteria are as unconnected to humans as living creatures, but they are necessary for human existence and life on Earth. Despite their reputation for causing ailments in humans ranging from tooth decay to the Black Plague, certain bacteria species are helpful to one’s health.
One symbiotic species in the human large intestine, for example, produces vitamin K, a vital blood-clotting component. Other species provide indirect benefits. Ruminant animals (cows, sheep and goats) can digest plant cellulose, and some plants (soybeans, peas, and alfalfa) can convert nitrogen to a more useful form.
Bacteria are responsible for the tangy flavour of yoghurt and the sour taste of sourdough bread. A diagram of the structure of the bacterial cell is given below:
Bacteria growth and multiplication
Bacteria divide through binary fission, which means that each cell divides into two daughter cells. Because nuclear division occurs before cell division, numerous cells with two nuclear bodies can be detected in an increasing population.
Bacterial growth may be split into two categories: increasing the size of individual cells and increasing the number of cells. Bacterial counts, both total and viable counts, can track population growth. The total count indicates the number of alive or dead cells, whereas the viable count indicates the number of living cells that can multiply.
The curve of bacterial growth
When bacteria are cultured in an appropriate liquid media and incubated, they develop predictably. A growth curve can be created by taking bacterial counts at intervals following a vaccination and plotting them against time. The phases of the growth curve are as follows:
Lag phase
There is no noticeable increase in the quantity of bacteria immediately after injection. However, the size of the cells may rise. This lag phase is the time necessary for adaptation to a new environment, and it varies according to species, type of culture, medium, and temperature.
Phase (logarithmic or exponential)
The cell begins to divide following the lag period, and its population grows exponentially over time.
Stationary phase
Cell division ends after a time of exponential development owing to nutritional depletion and hazardous product build-up. The viable count remains constant because there is a balance between dying cells and freshly produced cells.
Declination stage
This is when the population begins to decline owing to cell death.
Bacteria are prokaryotes with chromosomes made up of a single closed DNA circle and no well-defined nucleus or membrane-bound organelles. They appear in various forms and sizes, from tiny spheres, cylinders and spiral threads to flagellated rods and filamentous chains. They may be found almost anywhere on the planet and can survive in some of the strangest and harshest environments on Earth.
The archaeans (also known as archaebacteria) are microscopic prokaryotic creatures that only thrive in harsh settings such as boiling water, super-salty pools, sulphur-spewing volcanic vents, acidic water, and deep below the Antarctic ice.
Bacteria have been shown to have existed for as long as 3.5 billion years, making them one of the oldest living species on Earth. Many scientists now assume that archaea and bacteria diverged roughly 4 billion years ago from a common ancestor. The ancestors of today’s eukaryotes separated from the archaea millions of years ago. Despite their apparent similarity to bacteria, the archaea are biochemically and genetically unlike bacteria as bacteria are to humans.
Factors affecting the growth of bacteria
Temperature, oxygen, carbon dioxide, light, pH, moisture, and salt content are all elements that influence the organism’s generation time.
Nutrition
Bacteria are nutritionally classed based on their energy needs and capacity to synthesise critical metabolites. Phototrophic bacteria get their energy from sunshine, whereas chemotrophic bacteria get their energy from chemical processes. Bacteria that can synthesise all of their organic molecules are called autotrophs, whereas those that cannot synthesise their metabolites are called heterotrophs.
Oxygen
Based on how oxygen affects their development and viability, bacteria are classified as aerobes or anaerobes. The growth of aerobic bacteria depends on the presence of oxygen. They might be obligate aerobes, such as cholera and vibrio, that can only develop in oxygen, or facultative anaerobes, typically aerobic but can grow without oxygen.
Conclusion
Bacteria have a single cell with a basic internal structure, and are tiny. They lack a nucleus, and their DNA floats freely in a mass that resembles twisted threads known as a nucleoid, or exist as discrete circular fragments known as plasmids. Ribosomes, spherical units in which protein is stored from various amino acids, are found in a bacterium cell. Most bacteria have two layers of protection: an inner cell membrane and an outer protective wall. There is no inner cell membrane in some bacteria, such as mycoplasmas, and some of them can have a third outer layer known as a capsule.