Certain types of single-celled organisms can change cell structure under challenging conditions such as a scarcity of nutrients in the environment. These resting cells, which do not grow or expend much energy on biological functions, have evolved to survive poor growth conditions. An akinete is one type of resting cell, with a characteristically thick wall and a store of nutrients inside. When favorable conditions develop in the environment around the akinete, then this resting cell bursts and releases multiple new cells, which begin growing as normal.
The Greek word for movement is kinetos; commonly, the letter "a" is placed before a Greek word to signify the opposite of what the word means. An akinete, therefore, refers to an object that does not move. The term is specific to a certain subgroup of bacteria called filamentous cyanobacteria, so called because they tend to grow in long filaments. Many other bacteria develop resting cells in stressful environments, but these are most commonly called spores rather than akinetes, as their characteristics tend to be different.
Cyanobacteria, like all bacteria, require food and appropriate environmental conditions to live and reproduce in. Environmental stresses can either kill off the bacteria altogether or trigger the active cells into going into an akinete resting state. Examples of pressures that can prompt the bacteria into changing state include a lack of environmental nitrogen, a change in light wavelength, or the presence of too many other cells competing for the same resources.
Typically, in a microbial population, once the individual cells have grown to take up the available space and eat the available nutrients, then environmental stress develops. Generally, in a population of cyanobacteria, the akinetes will develop at this time, and not when the population still has room and nutrients to grow. In a watery environment, for example, a high cyanobacteria population can make the water cloudy. This cloudiness blocks some light wavelengths and the cells can recognize these changes, which may push the microbes into a resting state.
Characteristics of an akinete include a very thick outer wall as well as a store of nutrients and genetic material inside. Due to storage requirements, the akinete is also larger than the regular, living cell. The interior of the cell bursts open when the cell senses the return of suitable conditions, and newly reproduced cells spill out in a filament arrangement. If these fresh new cells can populate the new environment, such as a pond that has been replenished with fresh meltwater, then they can grow and reproduce until the point where the same cycle has to repeat itself.
