Bacterial capsules: no barrier against Bdellovibrio.

Bdellovibrio bacteriovorus 109J attached to both capsulated and non-capsulated Escherichia coli K29 cells. Electron microscopy revealed penetration of the thick polysaccharide capsule without any major disintegration of the neighbouring capsular matrix. The capsule remained intact during bdelloplast formation and lysis was unaffected by capsulation of the prey cell. This study shows that, in contrast to its effect on bacteriophage penetration and its protective activities against immune defence mechanisms, the capsule of E. coli does not serve as a barrier against invasion by B. bacteriovorus.