Roles of cytoskeletal proteins in the predatory life cycle of Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus are small, predatory bacteria that grow within the periplasmic space of a host bacterium. Bdellovibrio has a biphasic life-cycle switching from a uni-nucleoid, growth-senescent ‘attack-phase’ to a novel, multi-nucleoid filamentous ‘growth-phase’, which elongates and divides, growing saprophytically within the periplasmic space of their prey. Little is known to date about Bdellovibrio developmental processes and cell division within this periplasmic niche. Recent publications have demonstrated that bacterial cytoplasms house highly organised matrices of protein structures, called the bacterial cytoskeleton. The Bdellovibrio processes of prey-cell entry, filamentous cell growth and division coordination brings cellular morphological changes and challenges that could be coordinated by cytoskeletal elements. Green Fluorescent protein (GFP)-tagging and gene knock out approaches were used to gain insights into the function of these elements including: an Intermediate filament like protein Ccrp, which has a role in the maintenance of cell morphology; two actin homologues, which appear to function at different points in the predatory cycle, MreB1 and MreB2; and a new type of cytoskeletal element designated ‘bactofilin’, which may have a role in cell division control. Recent advances in GFP technologies have led to the development of optimised GFP variants, such as mTFP1 and mCherry. These have been used to reveal previously unseen detail of Bdellovibrio development within prey. Bdellovibrio do not follow the familiar pattern of bacterial cell division by binary fission, instead divide synchronously at multiple sites along their length, once prey resources are depleted. This yields both odd and even numbers of progeny Bdellovibrio.