Members of the Microbial World

Microbe is a microscopic organism. They are diversely distributed and habituated anywhere and everywhere. They are prevalently present in biosphere components such as water, air, soil, earth’s crust, plants, animals and higher organisms. Microbes can be beneficiary organism or pathogenic organism.

Classification of microbes

Microorganisms are found almost in every part of universe. Microbes are broadly classified in to two types as mentioned below.

• Prokaryotes
• Eukaryotes

Prokaryotic organism

They are smaller in size. Prokaryotic organisms are found enormous in planet. They are found in water, soil, gastro intestinal tract of higher organism and in atmosphere. Prokaryotes are not having cell nucleus and other cell organelles. Mostly prokaryotic organisms are unicellular organism. It is rare evident for a prokaryotic cell to be complex in structure and nature. Prokaryotes are further classified into two major sub domains.  

• Bacteria
• Archaea

Bacteria

They are not visible by human naked eye and grow at a very high speed. A bacterium has the ability to grow every 20 minutes. Exception is Thiomargarita namibiensis. It has no cellular bound organelles. Being individual cell bacteria can reproduce by binary fission or at times by budding. They never reproduce sexually. Individual cells aggregate to form multicellular colonies. Bacterial cell wall provides physical strength, support and rigidity for the cells. Bacterial genome has DNA of single loop. When part of it is transferred it is referred as plasmids. This plasmid helps in transfer of DNA information by bacterial conjugation process. Bacteria are matter of survival and are not meant for reproduction.

Archaea

Similar to bacteria, archaea is also an organism made of single cell. They are prevalently found in extreme environmental conditions like hot springs. Crenarchaeota is an Archean found in ocean sediments that are 150m depth. Archaean found in soil plays a major role in oxidation of ammonia. The difference between archaea and bacteria is not clearly understood earlier. Archaea falls under Monera kingdom. Later a microbiologist named Carl Woese in the year 1990 defined a three domain system which differentiates bacteria, archaea and eukaryotes from each other. Archaea and bacteria share different mechanism for genetic and biochemistry process. Bacterial cell wall membranes are made up of phosphoglycerides, an ester bond whereas Archaean cell wall membranes are made up of lipids, an ether bond. 

Eukaryotic organism

Eukaryotes are visible to naked eye as they are larger in size. They are larger than prokaryotes. They have cell nucleus, choloroplast, mitochondria and golgi bodies. Cell nucleus has DNA as its genome. Eukaryotic DNA is arranged as Chromosomes. Cell organelle like mitochondria helps in metabolism. Oxidative phosphorylation and citric acid cycle takes place in mitochondria. The plant cells have choloroplast as their cell organelles in similar to bacterial choloroplast. In plants choloroplasts helps in production of energy by photosynthesis process from light. They are mostly multicellular organisms and some are haploid or diploid cells. Single celled eukaryotes are referred as unicellular eukaryotes. They are classified as follows

• Protists
• Fungi
• Plants
• Animals

Protists

Protists are unicellular eukaryotes and are visible under microscope. As they are diversified through out the atmosphere it is not that easy to classify the protist.  Mostly algae are multicellular protist. Slime molds are protist which can exist in colonies, single celled or as multicellular species. The identify task of protist is still under research and hence number of protozoan species are not sure.

Fungi

Fungi are unicellular eukaryotic cells. They can reproduce asexually or sexually. Asexual reproduction is either by binary fission, budding or conidia formation and sexual reproduction is by basidiospore formation. It can be either benefit or harm the human kind. For instance fungi like Sacchromyces cerevisiae or bakers yeast is used in baking process.  Candida albicans are pathogenic fungi resulting in phenotypic switching.  

Plants

Green algae are photosynthetic eukaryotes comprising many numbers of microorganisms. Some are even protists and some are charophyte.  They are either unicellular or found in colonies. Green algae species are 6000 in number.

Animals

They are multicellular eukaryotes. Unicellular animal eukaryotes are not seen by naked eye. For instance arthropods like dust and spider mites, crustaceans like copepods and cladocera, aquatic eukaryotes like rotifers and nematodes are microscopic. These micro animals can reproduce sexually or asexually.