On a nutrient media like agar, bacteria can be grown in colonies in laboratories, which appear as a solid mass when seen through the naked eyes. Studying certain characteristic features of these colonies can be helpful in identifying the type of bacteria growing in it. Practice of identification of bacterial colonies in plates is called as colony morphology. Some of these colony characteristics are:
1. Shape of the colony: We can predict the type of the bacteria growing on the plate by the shape of the colony. Different bacterial colonies can have different shapes like round, filamentous, irregular, etc. Size of the colony also matters.
2. Edge of the colony (can be seen through a magnifier): The edge of a colony can also be helpful characteristic in distinguishing between different bacterial colonies. Some bacterial colonies have smooth edges, while some have irregular edges.
3. Color of the Colony (Chromogenesis): Bacterial colonies have different pigments like red, purple, green, yellow, etc. This is a very important feature that can be used to identify and distinguish bacteria.
4. Opacity of Colony: Bacterial colonies can be transparent, translucent or iridescent.
5. Surface of the Colony: Surface of the colony can be smooth, irregular, dull, glossy, etc.
The characteristics of bacteria in colonies is encoded by genes. So this remains constant in a particular species of bacteria. For example, a particular species of bacteria will always grow in a particular shape, and so on.