![]() ![]() (a) Vegetative growth occurs by binary fission when nutrients are plentiful. is synthesized as an inactive precursor whose activation by proteolitic processing in the mother-cell compartment isįIGURE 25.1 Life cycle of Bacillus subtilis. Activation of in the fores-pore depends on polar septation. The regulation of events in the mother cell and the forespore is due to the presence of four different sigma factors, two in each compartment, which assures that each genome gives rise to a different set of products (Fig. The mother cell is discarded by lysis after the completion of sporulation. The forespore ultimately becomes a metabolically quiescent and stress-resistant spore that can give rise to future progeny by germination when conditions improve. The genome of the mother cell provides the components for constructing the spore exterior and the genome of the forespore provides the components for constructing the spore interior. The subsequent engulfment of the prespore by the mother cell compartmentalizes the prespore inside the mother cell (Fig. The initiation of sporulation by the formation of a polar septum instead of the vegetative midcell septum requires the accumulation of a sufficient concentration of SpoOA~P. The integration of the extracellular and intracellular signals is regulated through a multicomponent phosphorelay that controls the prosphorylation of the transcriptional regulator SpoOA. Before initiating sporulation, cells monitor many intracellular factors, such as DNA replication and the TCA cycle. However, if cells are at a low density, the chances of finding additional nutrients is higher and sporulation less desirable. It may be that if starving cells are at a high density, it is better to sporulate rather than compete for nutrients. Cell density is also important for efficient sporulation, presumably to ensure that cells are sufficiently abundant. The primary signal for the initiaton of sporulation is nutrient starvation. From a practical point of view, it may be suggested that a window of time does exist before sporulation occurs in attached Bacillus biofilms highlighting the need for shorter operating runs between cleaning and sanitation of food-processing equipment surfaces.Endospore formation has been found exclusively in gram-positive bacteria and is best understood in Bacillus subtilis. subtilis cells may be stimulated to form spores when exposed to conditions of nutrient limitation. Results suggested that an existing biofilm of vegetative B. subtilis SpoIVFB-GFP biofilm cells began fluorescing after 30 h. subtilis SpoIVFB-GFP cells began fluorescing after 5 h, while B. ![]() ![]() Sporulation in corresponding planktonic cells was also monitored for comparative purposes. These biofilms were subsequently exposed to nutrient limitation to stimulate spore formation, which was monitored for fluorescence by confocal scanning laser microscopy. ![]() 8 log CFU/ml vegetative cells and spores below the lower detection limit (i.e., <1 log CFU/ ml) were allowed to develop on glass wool (37 degrees C). Spore formation by a Bacillus strain (Bacillus subtilis SpoIVFB-GFP) engineered with a green fluorescent protein (GFP) fused to a polytopic membrane protein (SpoIVF) that fluoresces during sporulation was observed. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |