Prey-derived signals regulating duration of the developmental growth phase of Bdellovibrio bacteriovorus

Abstract

The filamentous elongation typical of growth-phase cells of the predatory bacterium Bdelovibrio bateriovorus is mediated by regulatory signals that are derived from the prey cell itself. These signals regulate the differentiation of growth-phase cells into the attack phase and appear to be required for continued filamentous growth by prey-dependent wild-type bdellovibrios and their prey-independent mutant derivatives alike. Using a prey-independent bdellovibrio strain, we have developed an assay for the detection and quantification of the growth-extending signal activity present in extracts of prey cells. This prey-derived regulatory activity was shown to be independent of its nutritional contribution to the bdellovibrios and was found to occur in heat-stable, proteinlike compounds of a variety of native molecular weights within the soluble fraction of extracts from both gram-negative and gram-positive bacteria.

Bdellovibrio host dependence: the search for signal molecules and genes that regulate the intraperiplasmic growth cycle

“…In accord, Gray and Ruby (6) found that prematurely released bdellovibrios would initiate DNA replication in a rich medium if it was supplemented with microbial cell extracts. The factor(s) responsible for stimulating DNA replication was apparently different from that responsible for the switch between attack phase and growth phase, since extracts that could stimulate DNA replication in prematurely released wild-type bdellovibrios had no effect on attack-phase cells.…”

Cell-cycle progress in obligate predatory bacteria is dependent upon sequential sensing of prey recognition and prey quality cues

“…However, we were unable to replicate these results. Follow-up studies found that although prey extracts sustained extracellular filamentous growth and DNA replication, they could not promote the differentiation of the nonreproductive AP cell to the GP (32)(33)(34)(35). This result suggested that two separate prey-derived cues, one in the soluble prey extract fraction and the other hitherto undefined, were necessary for the AP-to-GP transition to occur (33).…”

“…The growth-promoting activity induced by the second cue is concentration dependent (35) but does not contribute directly to nutrition (34,35). We propose that its occurrence may signal that enough prey-derived nutrients are present in the intracellular medium to support growth, thereby acting as a marker of prey quality and enabling growth initiation.…”

“…This transitory phase can be maintained for 1 h, the time that elapses between prey entry and initiation of growth (34), during which the bdelloplast's cytoplasmic membrane becomes completely permeable to small molecules (58). Relief from this point and progress into the GP requires that the second, soluble cue, probably originating from the prey cytosol (35), be released into the periplasm of the bdelloplast, where the predator can sense it. Thus, consequent to spatial separation, the sensing of the first, envelope-borne cue is temporally separated from the sensing of the second, cytosolic cue, bringing about successive waves of change in gene expression.…”

“…One cue presumably elicits the predatory process, promoting prey penetration, bdelloplast formation, and prey consumption (32,33). A second soluble cue promotes DNA synthesis and is required for sustained cellular growth (33)(34)(35).…”