Bacteria are unicellular,small organisms present all around us and can only be seen with the help of microscope.Bacteria are different shapes i.e rod,spiral,round etc.Some have a tail-like structure called flagella,which helps them to swim.
The three most common bacterial cell shapes are cocci (spherical, from the Greek word for seed/berry), bacilli (rod-shaped, from the Greek word for staff), and spirilla (curved shape, from spiral). There are various ways of subdividing these three overarching shapes mostly based on how they are arranged into multicellular organizations. These diagrams give a good overview of the various bacterial morphologies (I couldn't decide which was better so I'm just including both).
The MreB protein is a major factor in controlling the shape of the cell. Although scientists haven't agreed upon the exact mechanism, mutations to the mreB gene are accompanied by unusual changes to cell shape. MreB probably directs how peptidoglycan is added to the cell wall as the cells grow and divide. The peptidoglycan cell wall serves as a rigid scaffold that helps the cell keep its shape under osmotic pressure. By controlling where peptidoglycan is added to the cell wall, MreB may control the shape of the cell as it grows and divides.
Below are some images of various cell shapes and arrangements based on the above diagrams. This is just a small taste of bacterial diversity.