Bacterial Inclusions

Introduction:

Bacterial cells are simple and have very few organelles within them. Unlike the eukaryotes, The cytoplasm of the Bacteria is loaded with few organelles among which comes the inclusions, formed by the gathering of the organic or inorganic substances. These bodies have a different role and exist in different forms such as the granules, crystals, globules etc. Since bacteria survive in nutrient deprived areas, They need to store certain nutrients or inorganic molecules such as phosphate, sulfur etc which are the important for the formation of various cell organelles such as the nucleic acids, amino acids. Some inclusions are not for storage purpose and are involved in various other activities such as the Aquatic magnetotactic bacteria have magnetosomes that help in orienting these bacteria according to the magnetic field of the earth. Various inclusions identified within the bacteria are explained further in short as below.

Storage inclusions: 

As the name suggests, these type of inclusions mainly include the granules or globules. Whenever there is a shortage of any of the nutrients, or there is a necessity of storing the end product of the metabolic pathway, these substances are stored in the form of either granules or the globules. Poly-beta-hydroxybutyrate(PHB) is an example of carbon storing granules. carbon storing granules are called as polyhydroxyalkonate granules and PHB is one such. These cellular bodies have gained lot of attention by the industrial microbiologists in the recent years because of their use in the manufacturing of biodegradable plastic. 

Polyphosphate granules are another group of inorganic inclusions which store inorganic phosphate and help in protecting the cell from starving conditions of the most important inorganic phosphate without which, the cell's energy source ATP and the nucleic acid, DNA of bacteria are incomplete. Sulfur globules are another kind of inorganic inclusions which help storing sulfur that is used as the source of electrons by some of the sulfur reducing bacteria. Glycogen, an important polysaccharide is also stored in the form of granules which is an important carbohydrate source to the bacterium.

Microcompartments:

There are some type of inclusions which serve functions other than storing substances. They are made up of proteins surrounded by a protein shell which is selectively permeable and does not allow any substance to pass through it. Carboxysomes are an example of the microcompartments present in the cyanobacteria which contain the enzymes that participate in carbon-dioxide fixation. The carbon-dioxide available in the atmosphere is utilized by the micro-organisms to produce sugars from it in the presence of the enzyme ribulose-1, 5-bisphosphate carboxylase/oxygenase(RubisCO). There is a polyhedron protein coat within the carboxysomes which is the site for the accumulation of carbon-dioxide, preventing it from escaping out of the cell. Nitrobacter, cyanobacteria and knallgasbacteria are some of the examples containing these structures and because of the high concentartion of enzymes and higher rate of conversion of bicarbonate to carbon-dioxide, there is higher rate of carbon-dioxide fixation.

Gas Vacuole:

Apart from the role in storing materials, there are also some inclusions used for some special characteristic of the Bacteria. Many photosynthetic bacteria residing in water bodies have some specialized inclusions called the gas vacuoles which help in creating buoyancy to make them float in their habitats. Gas vesicles are the small hollow cylindrical structures, containing walls made up of single protein and are impermeable to water. Since these organisms live in water, they need to be impermeable to water and allow the atmospheric gases to pass through it. The maintenance of buoyancy helps these micro-organisms to reach the levels within water where they can carry out the process of photosynthesis, an important phenomenon of the photosynthetic bacteria.

Fate of the Bacteria in the absence of these vacuoles:

Had there not been these vacuoles, What would be the fate of these tiny organisms which can never survive in nutrient deprived, extreme conditions.Storage vacuoles such as the glycogen vacuoles are always helpful in providing food reserves under deprived conditions of food. Phosphate granules help the bacteria withstand the deficiency of phosphate, which stands out to be the most important component of the bacterial cell. For the aquatic bacteria, these vacuoles help in providing buoyancy and without their presence, these bacteria would not have been able to maintain at appropriate levels within water without getting drowned and killed. Carboxysomes like structures on the other hand are very effective in helping the process of fixation of carbon dioxide to be carried out in a successful manner.  

References:
1) Joanne M. Willey, Linda M. Sherwood, Christopher J. Woolverton. Prescott's Microbiology Ninth Edition. United states of America: McGraw-Hill, 2014.Print.

2) Boundless. "Carboxysomes." Boundless Microbiology Boundless, 27 May. 2016. Retrieved 14 May. 2017 from https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/cell-structure-of-bacteria-archaea-and-eukaryotes-4/specialized-internal-structures-of-prokaryotes-36/carboxysomes-268-4344/

3)  Kara Rogers and Robert J. Kadner(2017, February 08) bacteria. Retrieved from https://britannica.com/science/bacteria/Genetic-content