∞ generated and posted on 2016.12.15 ∞

Single, moderately well-delineated entity possessing multiple cells but little or no cellular differentiation.

A Colony is a group of cells or organisms that typically have descended from a single parent, to some degree are separate individuals despite being found within a colony in very close spatial association, and usually though not quite always substantially resemble each other phenotypically within the colony; whether the colony or instead its constituents represents the 'individual' organism is an open question.

Colonial forms are seen in various simple but multi-celled algae as well as numerous bacteria. The former often are planktonic (free floating) while the latter are often benthic, forming what are known as microcolonies on numerous surfaces.

Colonies of cells often lack the sophisticated cellular differentiation seen with true multicellular organisms, particularly in terms of lacking a clear distinction between soma and germline cells. Some degree of differentiation still occurs within colonies of many of these organisms, however, resulting in different cells taking on distinctly different functions.

In microbiology, colonies that form in association with solid media, such as can be found in Petri dishes, correspond to the growth of individual cells to large numbers while constrained to a single location by the gel structure associated with agar-based culture media. See, e.g., colony-forming unit.

Figure legend: Illustration of how a colony can form, starting with any number of cells (left), and that the resulting colony will look pretty much the same (right) unless it was started with an extremely large number of cells. In any case, the cells from which the colony is initiated would be found, at the start of colony formation, more or less at the center of resulting colony. We thus employ the term colony-forming unit (a.k.a., CFU) to describe the colony-forming cells because we can't be sure, from looking at a colony, that it was initiated with one versus many initial cells.

The first 30 or so seconds of the following video shows time-lapsed growth of colony and also shows other aspects of microscopy of Legionella including fluorescence microscopy:

The following video shows bacteria repeatedly dividing and thereby forming into a microcolony: