Summarizing Prokaryotic Diversity

Summary

Prokaryotes existed for billions of years before plants and animals appeared. Hot springs and hydrothermal vents may have been the environments in which life began. Microbial mats are thought to represent the earliest forms of life on Earth, and there is fossil evidence of their presence about 3.5 billion years ago. A microbial mat is a multi-layered sheet of prokaryotes that grows at interfaces between different types of material, mostly on moist surfaces. During the first 2 billion years, the atmosphere was anoxic and only anaerobic organisms were able to live. Cyanobacteria evolved from early phototrophs and began the oxygenation of the atmosphere. The increase in oxygen concentration allowed the evolution of other life forms. Fossilized microbial mats are called stromatolites and consist of laminated organo-sedimentary structures formed by precipitation of minerals by prokaryotes. They represent the earliest fossil record of life on Earth.

Bacteria and archaea grow in virtually every environment. Those that survive under extreme conditions are called extremophiles (extreme lovers). Some prokaryotes cannot grow in a laboratory setting, but they are not dead. They are in the viable-but-non-culturable (VBNC) state. The VBNC state occurs when prokaryotes enter a dormant state in response to environmental stressors. Most prokaryotes are social and prefer to live in communities where interactions take place. A biofilm is a microbial community held together in a gummy-textured matrix.

Glossary

acidophile

organism with optimal growth pH of three or below

alkaliphile

organism with optimal growth pH of nine or above

anaerobic

refers to organisms that grow without oxygen

anoxic

without oxygen

biofilm

a microbial community growing together on a surface, often held together with a gummy matrix

cyanobacteria

bacteria that evolved from early phototrophs and oxygenated the atmosphere; also known as blue-green algae

extremophile

organism that grows under extreme or harsh conditions

halophile

organism that require a salt concentration of at least 0.2 M

hydrothermal vent

fissure in Earth’s surface that releases geothermally heated water

hyperthermophile

organism that grows at temperatures between 80–122 °C

microbial mat

multi-layered sheet of prokaryotes that may include bacteria and archaea

nutrient

essential substances for growth, such as carbon and nitrogen

osmophile

organism that grows in a high sugar concentration

phototroph

organism that is able to make its own food by converting solar energy to chemical energy

psychrophile

organism that grows at temperatures of -15 °C or lower

radioresistant

organism that grows in high levels of radiation

resuscitation

process by which prokaryotes that are in the VBNC state return to viability

stromatolite

layered sedimentary structure formed by precipitation of minerals by prokaryotes in microbial mats

thermophile

organism that lives at temperatures between 60–80 °C

viable-but-non-culturable (VBNC) state

survival mechanism of bacteria facing environmental stress conditions