Cannibalism by Sporulating Bacteria

Speaker: 陳吟竹

Commentator: 吳俊忠 老師

Time: 2003/10/08, 15:00-16:00

Place: Room 601

Bacillus subtilis responds to signals that reflect high population density and nutritional limitation by entering a rest state as an endospore, in which they remain inactive and dormant for many years. Central to the initiation of sporulation is the activation of the transcription regulatory protein Spo0A by phosphorylation [1]. The authors discovered two operons, skf (sporulating killing factor) and sdp (sporulating delay protein), that are strongly induced at the start of sporulation under the control of Spo0A. And the mutations accelerated spore formation. In this paper, by construction of several mutants, they showed that the skf operon is involved in the production of an extracellular killing factor and formation of an export pump which pumps the killing factor out of the cells and confers resistance to the killing factor during sporulation. The second operon, sdp, produces a 5 kDa extracellular factor, SdpC, that acts as a signaling protein among bacteria. SdpC strongly controls the transcription of a two-gene operon, yvbA and yvaZ, which is related to an ATP synthetase operon. Otherwise, YvbA was previously identified to inhibit the expression of the gene for s^w, which could heighten sensitivity to the killing factor by suppressing the antibiosis stress response. Conclusively, upon nutrient limitation, Spo0A is activated only in a subpopulation of cells. These Spo0A-activate cells produce the killing factors and the Spo0A-inactive cells are lysed. Spo0A-activated cells also produce the pump to protect themselves. Additionally, sdp operon is activated to turn on the synthesis of YvbA, which, in turns, causes an increase in lipid oxidation and ATP production. YvbA also acts cooperatively with the killing factor to cause cell lysis. As a result, nutrients are releases, providing food for Spo0A-active cells, which enables them to keep growing rather than entering sporulation[2]. Because the process of sporulation is irreversible after its earliest stage, delaying spore formation might be beneficial. This cannibalistic phenomenon could be seen as a new bacterial “programmed cell death” system and support a new way of looking at bacterial cultures as multicellular organisms [3].

References:

1.     Piggot PJ (1996), Spore development in Bacillus subtilis. Curr Opin Genet Dev, 6: 531-537

2.     Gonz’alez-Pastor JE, EC Hobbs, and R Losick (2003), Cannibalism by sporulating bacteria. Science, 31: 510-513

3.     Engelberg-Kulka H and R Hazan (2003), Cannibals defy starvation and avoid sporulation. Science, 31: 467-468