Microbes overview

Microorganisms are an extremely diverse group of organisms made up of fungi, archaea, protists (algae), plankton and planarian amoungst others. Most are unicellular, but a few are unicellular.

They live in all parts of the biosphere where there is liquid water, including soil, the sea bed, the atmosphere, rocks, plants and animals. They are also critical to nutrient recycling and act as decomposers in ecosystems. Some can fix nitrogen and are a vital part of the nitrogen cycle.

Single celled microorganisms were the first life forms on earth, dating back to approximately 3 to 4 billion years ago. Bacteria, algae and fungi have been identified in amber over 220 million years old. Most can reproduce rapidly, and microbes such as bacteria can also freely exchange genes by conjulation, transformation and transduction between widely divergent species. This and mutation rates allows them to rapidly evolve to survive in new environments and stresses, playing a vital role in medical research.

The idea of microbes existence was discussed for many centuries before their identification in the 17th century by Anton Leevwenhoek who invented the first microscope, which lead to the discovery of many areas of medicine and micro biology.

Classification

Prokaryotes

Organisms that lack a cell nucleus and membrane bound organelles. Almost always unicellular, some species such as myxobacteria can morph into complex structures through their life cycle. They consist of 2 domains; Bacteria and Archaea. Prokaryotes are the most diverse and abundant group of organisms on the planet. They are found in practically all environments where some liquid water is available and up to 140c. They exist in sea water, soil, air, animals, beneath the earths crust and pretty much every surface which hasn't been specially sterilized, and are an estimated 5 million trillion trillion on earth.

Bacteria

Nearly all invisible to the naked eye, with very exceptions such as Thiomargarita nambiensis. They are unicellular organisms with no membrane bound organelles. Their genome is usually a singular loop of DNA although they can harbor small pieces of DNA called plasmids. They reproduce by binary fission or budding and can double as quickly as every 10 minutes.

Archaea

Very similar to bacteria only described in 1990 by Carl Woese with the introduction of his 3 domian system. They differ from bacteria in their genetics and biochemistry. Bacteria membranes are made from physphoglycerides with ester bonds, archaea membranes are made up of ether lipids. Archaea were first thought only to exist in extreme conditions, but is now known to be untrue eg. Crenarchaeota is the most common life form in the sea and is abundant in soil being vital to ammonia oxidation.

Eukaryotes

Most living things that are visible to the naked eye in adult form are eukaryotes, however a large number are also microorganisms. They contain a cell nucleus and evolved from symbiotic bacteria, therefor contain a remnant genome. Like bacteria plant cells have cell walls and contain organelles such as chloroplasts, produce energy through photosynthesis and were originally symbiotic bacteria.

Protists

Commonly unicellular and microscopic. They are a highly diverse group difficult to identify. Include many species of algae and slime molds switching between unicellular, colonial and multi cellular forms.

Animals

Include microscopic arthropods, copepods, cladocera, nematodes and rotifers (water filter feedrs). Reproduce both Asexually and sexually.

Fungi

Many unicellular species including bakers yeast. Some undergo phenotypic switching and grow as single cells in some environments and filamentoushyphae in others. Reproduce both Asexually by budding or binary fission and spores called condia, and basidiospores sexually.

Plants

There are approximately 6000 species of green algae. They are a group of eukaryotes and can be classified as protists, others like charophyta are classified with embryophte plants. Algae can grow single cells or long chains. Green algae include unicellular and colonial flagellates.

Extremophiles

Microorganisms adapted to survive and thrive in conditions normally fatal to most life forms eg. Temperatures as high as 130c and pressures as low as 0atm (vacuum of space).

( extracted from www.wikipedea.com)