E

FIGURE 9.05 Spore Formation in Bacillus

Bacillus (A) first duplicates its DNA (B), then walls off the new DNA into a spore that lies within the cell (C and D). The spore is released from the original mother cell as it bursts and dies (E).

FIGURE 9.06 Spore Formation in Bacillus anthracis

Transmission electron micrographic image of Bacillus anthracis from an anthrax culture, showing cell division (A), and spores (B). Public Health Image Library (CDC) by Dr. Sherif Zaki and Elizabeth White.

FIGURE 9.06 Spore Formation in Bacillus anthracis

Transmission electron micrographic image of Bacillus anthracis from an anthrax culture, showing cell division (A), and spores (B). Public Health Image Library (CDC) by Dr. Sherif Zaki and Elizabeth White.

several genes in the mother cell, including the gene that encodes pre-oK. As a result, pre-oK accumulates in the mother cell. The presence of oG in the spore allows transcription of late sporulation genes in the spore, including factors that move into the mother cell and activate pre-oK to active oK (Fig. 9.07). Each of these sigma factors is responsible for the transcription of a group of genes needed for successive stages in the development and release of the spore.

The cascade of regulators seen in spore formation ensures that steps in a complex series of events follow each other in the correct sequence. Each regulator controls one stage in the process and also controls the regulator for the next stage. In addition,

FIGURE 9.07 Outline of Spore Formation Regulatory Cascade

A cascade of four sigma factors is involved in the stepwise development of the spore in Bacillus. An external signal activates synthesis of oF in the spore. This is required for transcription of the gene for oG (inside spore) and for factors that cross into the mother cell (red arrow) and convert pre-oE into active oE (in mother cell). Active oE is required for synthesis of the precursor, pre-oK. Finally, oG allows synthesis of factors that cross into the mother cell (red arrow) and convert pre-oK into active oK (in mother cell).

regulatory signals are exchanged between more than one cell. Thus, the developing spore and mother cell cross-regulate each other. The development and differentiation of higher organisms use much the same principles as spore formation, but the regulatory schemes are vastly more complex.

Positive regulatory factors are often opposed by negative factors.

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