Prokaryote Survival in Changing Environment
Prokaryotes are commonly known as bacteria or micro-organisms; they are many in number and are found almost everywhere, both on living and non-living organisms. They reproduce through an asexual process called binary fission and can replicate to millions of bacteria within a few hours and this component aids in their pathogenesis. This essay will lay emphasis on how prokaryotes adapt to changes in the environment. Prokaryotes are divided into eubacteria and archeabacteria. Eubacteria is the most studied currently while archeobacteria are able to thrive in extreme environments. When the environment is unfavorable bacteria adapt several mechanisms to survive. One of them is spore formation where spores are produced and remain in a vegetative state until the environment is favorable to reproduce again. Some mutate into cells with new and diverse characteristics that are able to thrive in harsh environment. A few bacteria undergo a process of reductive division where a cell yields a population of daughter cells that are smaller in size thus have reduced level of metabolism that increase chance of survival in a nutrient deprived environment. Lastly bacteria change their morphological appearance in different environment circumstances, some elongate to increase the surface area over which diffusion process takes place in cases of nutrient deprived environment, other change shape for motility and to avoid being desiccated.
All living things are made of cells and are classified into two main groups; micro-organisms are classified as prokaryotes, while other living things like animals, plants, fungi are classified as eukaryotes. The word prokaryote means “before a nucleus”. The most familiar term used for prokaryotic cell is “bacterial cell”. They are the most numerous and are found everywhere ranging from soil, air, oceans and even our bodies (Cuthbert, 513).
It is smaller in size as compared to eukaryotic cell. They vary in shape from spiral, rod shaped and coccus. The cell of prokaryote is surrounded by glycocalyx which is usually a polysaccharide or polypeptide and aids in attachment to surfaces. The cell wall also protects the cell from phagocytosis which is an important element of the body’s protection against micro-organisms. Most of the cells have flagella that aids in propulsion, some have capsules that is made of polysaccharide layer and protects against desiccation and phagocytosis. When capsules are present, flagella are not. Most bacterial cells posses fimbrae that are shorter than flagella and help the cells adhere to surfaces especially mucous membranes, they also aid in transferring DNA from one cell to another aiding in pathogenicity (Cuthbert, 512).
The cell has an internal cell wall that has a cytoplasmic membrane that encloses the cytoplasm. The cytoplasms mainly consist of phospholipids and proteins and lacks carbohydrates or sterols. The chromosome contains a distinct, spherical molecule of DNA found in the nucleoid. Prokaryotes DNA interacts with the cytoplasm and has no nuclear membrane, this is unlike the eukaryotic cells whose DNA is separated from the cytoplasm by a nuclear membrane (Cuthbert, 512).
Classification of prokaryotes
Are divided into two main groups namely; eubacteria and archaebacteria. Eubacteria is the commonest and the most studied and is found almost everywhere except in extreme environment, archeabacteria on the other hand are mainly found in extreme environment. Examples of archeabacteria are; Thermoacidophiles that live in hot and acidic environment, they cannot thrive in temperature lower than 55 degrees Celsius; they are anaerobes and cannot thrive in presence of oxygen. Halophile is another group that lives in salty environments like the Great Salt Lake that contains as much as 15% salt concentration. Lastly, there is the methanogens, a group that are obligate anaerobes and use carbon dioxide to give off methane, they are mainly found near volcanic areas, sewage treatment plants and swamps (Hogan & Monosson, n.p)
Prokaryotes reproduce through an asexual process termed as binary fission. The original chromosome replicates and separates into two and the two cells start to separate, at the same time the cell elongates and becomes larger, finally a plasma membrane and cell wall forms and separates the two identical cells. The process occurs quickly, and when the conditions are favorable a single cell can replicate to billions of cells in just 10 hours, this is an important aspect that aid in their pathogenicity (Kunte, 3).
Survival mechanisms in a changing environment
Extreme environment can be described as that with lower species diversity and fewer living organisms in general. When the environment is unfavorable, bacteria has several mechanisms to help in their survival. Some produce endospores; a dormant cell that can withstand harsh environments like in extreme heat, cold or ultraviolet radiation. The spore coat surrounds the bacteria’s chromosome and when the environment becomes favorable, the endospores grow into a new bacterial cell. When in spore form the cell is able to conserve its energy reserves as a result of lower metabolic activity. Spore development cannot be termed as a reproductive state but as a survival tactic. Examples of bacteria that produce spores are bacteria that cause botulism, anthrax and tetanus (Kunte, 5)
In an environment in which bacteria’s are not accustomed to or unfavorable, some form genetic mutations where there are changes in DNA sequence that leads to bacteria with new forms of genes with diverse characteristics that may have the perfect combination to thrive in harsh environments (Roszakt &Colwell, 371).
Some bacteria have reductive division in response to nutritional starvation or unfavorable environment. The cells yield a population of daughter cells that are smaller in size as a result has reduced level of metabolism thus there is maximum utilization of the limited endogenous substrate thus increasing chances of survival (Roszakt &Colwell, 371).
The vibrio cholerae class of bacteria adapts to a changing environment like that of reduced nutrient availability by decreasing the cell volume, the small cell is able to adjust to the substrate limited environment and can be able to endure stressful events in the environment by adjusting appropriate physiological processes (Roszakt &Colwell, 371).
The cell has two main mechanisms to keep the interior in balance with the surrounding environmental stress. Halophiles for example are able to withstand the highly osmotic conditions in the environment through these mechanisms. There is the ‘salt-in’ mechanism where sodium ions are excluded from the cytoplasm so as to maintain the osmotic balance with the external environment; instead the cell accumulates high levels of potassium inside the cell (Atanasova, 17).
The second mechanism is the ‘organic-osmolyte strategy’ where the organism synthesizes small organic molecules like glycerol, glycine betain that prevents loss of water from the cell. There is accumulation of highly soluble organic compounds from the surrounding environment and may include polyols and amino acids has help in maintaining the cell’s osmotic balance. The organic compound also acts as a stabilizer of the whole cell in cases of extreme heat, freezing, thawing or desiccation (Atanasova, 18).
How morphological shape affects cell survival in different environmental conditions
The shape a bacterium adapts has a biological relevance to how they respond to environmental changes and during the pathogenesis process. Bacteria may change the cell morphology in cases of reduced nutrient availability. The change in cell shape leads to increased surface area over which diffusion of nutrients across the cell membrane can take place thus enhancing the nutrient harvesting efficiency. An example is Caulobacter crescentus that has a long stalk to increase the surface area of diffusion, the stalk becomes longer in nutrient deprived states (Young, 2).
Some change their morphological shape for the purpose of motility. Fast cells are mainly rod- shaped, while curved cells are usually slower in terms of speed. Cells that navigate viscous environments adapt to a slightly curved or spiral shape. Cells that move in a group have a morphological constraint as compared to those that move individually. The ones in groups are mostly non-motile because the cells cannot align properly. The above clearly shows that the cells must adopt different shape ratios in line with the environment (Young, 3).
Lastly bacteria change shape in cases of predation. They develop certain shapes to escape capture, by either reducing their cell size, being extremely fast or by making themselves inaccessible by growing in aggregates or bio-film. Some resist ingestion by becoming longer and curved. An example is cyanobacterium Arthrospira that grows in helical trichomes mainly to avoid predation (Young, 3).
Advantages of prokaryotes
Although some bacteria are known to cause disease, some are useful to humans, animals and even plants. Some are ‘nitrogen fixing bacteria’ and convert nitrogen in the atmosphere in a form that can be easily absorbed by plants. They are used in processing of many foods like yoghourt, buttermilk and cheese. Some live in the digestive tract of humans, like Escherichia coli lives in the gut and produces vitamin k that human absorb and use in blood clotting process in return the bacteria has food and a warm place to live. They have a symbiotic relationship with plants and animals. Lastly they help soil decompose dead organisms thus sustaining chemical cycles in the environment (Cuthbert, 11).
Although prokaryotes cause half of human diseases they are still very important in the biosphere and if they did not exist the survival of any other life would diminish. They play a major role in recycling chemical components between the living and the living. Their short generation time allows them to evolve very fast thus further research need to be conducted on Prokaryotes so as to find out more on their symbiotic advantages to the human species.
Atanasova. S. Nina. Prokaryotic Microorganisms, Viruses, and Antimicrobial Agents From hyper-saline Environments. 2013. (Web. 19th March, 2015).
Cuthbert, Colin. Bacteria, Viruses, Protists and Fungi. (Web. 19th March, 2015)
Hogan, Michael. & Monosson, Emily. Archea. Encyclopedia of life. 2010. (Web. 20th March, 2015)
Kunte, Jorg . Osmoregulation in Halophilic Bacteria. Encyclopedia of life support systems.2013. (Web. 20th March, 2015)
Roszakt. D.B & R. R. Colwell. R. Survival Strategies of Bacteria in the Natural Environment.2012. (Web. 19th March, 2015).
Young. D. Kevin. Bacterial Morphology: Why Have Different Shapes? National Institute Of Health. 2007. Vol 10 Is 6: 596-600.