Pseudomonas putida Capsule

Pseudomonas putida is a gram-negative, rod-shaped bacterium in the protobacterial lineage. While this species is not pathogenic, it can make a capsule like many of its pathogenic cousins. Made of complex polysaccharides, this capsule plays a role in helping the bacterium attach to surfaces, and may provide the cell with protection from desiccation (and phagocytosis). Together, these images provide good examples of the capsule structure and of two common types of microscopy: phase-contrast and fluorescent.

Figure 1 shows a single dividing cell of P. putida viewed with a bright-field microscope under phase-contrast. The phase-contrast provides a natural contrast between the cellular and capsular material.

Figure 2 shows the field stained with a fluorescently tagged polyclonal antibody made against the capsular material and viewed under fluorescent light. The antibody binds specifically to the capsule, providing more of a contrast between the cell and its capsule.