Courtesy: Master of Science in Microbiology (M.Sc.Microbiology)

Prokaryotes

Prokaryotes lack membrane-bound organelles, such as mitochondria or a nucleus. Instead, most prokaryotes have an irregular region that contains DNA, known as the nucleoid. Most prokaryotes have a single, circular chromosome, which is in contrast to eukaryotes, which typically have linear chromosomes. Nutritionally, prokaryotes have the ability to utilize a wide range of organic and inorganic material for use in metabolism, including sulfur, cellulose, ammonia, or nitrite. Prokaryotes are relatively ubiquitous in the environment and some (known as extremophiles) thrive in extreme environments. # ISO certification in India

Bacteria

Modern stromatolites in Shark Bay, Western Australia. It can take a century for a stromatolite to grow 5 cm.

Bacteria are one of the world’s oldest forms of life, and are found virtually everywhere in nature. Many common bacteria have plasmids, which are short, circular, self-replicating DNA molecules that are separate from the bacterial chromosome. Plasmids can carry genes responsible for novel abilities, of current critical importance being antibiotic resistance. Bacteria predominantly reproduce asexually through a process called binary fission. However, about 80 different species can undergo a sexual process referred to as natural genetic transformation. Transformation is a bacterial process for transferring DNA from one cell to another, and is apparently an adaptation for repairing DNA damage in the recipient cell. In addition, plasmids can be exchanged through the use of a pilus in a process known as conjugation.# ISO certification in India

The photosynthetic cyanobacteria are arguably the most successful bacteria, and changed the early atmosphere of the earth by oxygenating it. Stromatolites, structures made up of layers of calcium carbonate and trapped sediment left over from cyanobacteria and associated community bacteria, left behind extensive fossil records. The existence of stromatolites gives an excellent record as to the development of cyanobacteria, which are represented across the Archaean (4 billion to 2.5 billion years ago), Proterozoic (2.5 billion to 540 million years ago), and Phanerozoic (540 million years ago to present day) eons. Much of the fossilized stromatolites of the world can be found in Western Australia. There, some of the oldest stromatolites have been found, some dating back to about 3,430 million years ago.# ISO certification in India

Clonal aging occurs naturally in bacteria, and is apparently due to the accumulation of damage that can happen even in the absence of external stressors.

Archaea

A bottom-dwelling community found deep in the European Arctic.

Hydrothermal vents release heat and hydrogen sulfide, allowing extremophiles to survive using chemolithotrophic growth.Archaea are generally similar in appearance to bacteria, hence their original classification as bacteria, but have significant molecular differences most notably in their membrane structure and ribosomal RNA. By sequencing the ribosomal RNA, it was found that the Archaea most likely split from bacteria and were the precursors to modern eukaryotes, and are actually more phylogenetically related to eukaryotes. As their name suggests, Archaea comes from a Greek word archaios, meaning original, ancient, or primitive.# ISO certification in India

Some archaea inhabit the most biologically inhospitable environments on earth, and this is believed to in some ways mimic the early, harsh conditions that life was likely exposed to^{[citation needed]}. Examples of these Archaean extremophiles are as follows:

• Thermophiles, optimum growth temperature of 50 °C-110 °C, including the genera Pyrobaculum, Pyrodictium, Pyrococcus, Thermus aquaticus and Melanopyrus.
• Psychrophiles, optimum growth temperature of less than 15 °C, including the genera Methanogenium and Halorubrum.
• Alkaliphiles, optimum growth pH of greater than 8, including the genus Natronomonas.
• Acidophiles, optimum growth pH of less than 3, including the genera Sulfolobus and Picrophilus.
• Piezophiles, (also known as barophiles), prefer high pressure up to 130 MPa, such as deep ocean environments, including the genera Methanococcus and Pyrococcus.
• Halophiles, grow optimally in high salt concentrations between 0.2 M and 5.2 M NaCl, including the genera Haloarcula, Haloferax, Halococcus.

Methanogens are a significant subset of archaea and include many extremophiles, but are also ubiquitous in wetland environments as well as the ruminant and hindgut of animals. This process utilizes hydrogen to reduce carbon dioxide into methane, releasing energy into the usable form of adenosine triphosphate. They are the only known organisms capable of producing methane. Under stressful environmental conditions that cause DNA damage, some species of archaea aggregate and transfer DNA between cells. The function of this transfer appears to be to replace damaged DNA sequence information in the recipient cell by undamaged sequence information from the donor cell.# ISO certification in India