Study on the Determination Mechanism of Flagellar Number in Bacterial Cell.

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During bacterial cell division cycle, various biosynthetic processes proceed under spatial and temporal controls and two daughter cells with the same structures are finally produced. Flagella can be considered as one of the most suitable systems to study genetic control of duplication of cellular constituents. Cytological study of Salmonella typhimurium indicated that the duplication of flagellar number occurs at the specific stage, the end of cell elongation period. However, it was found that, in the strains defective in the gene for anti-sigma factor specific for flagellar regulon, de novo synthesis of flagella occurs throughout cell elongation period. This result indicates that a negative feedback control exerted by the anti-sigma factor plays an important role in duplication process of flagellar number. As the cell elongates, the cell volume increases and the intracellular concentration of anti-sigma factor decreases, which allows the flagellar regulon expressed and results in initiation of de novo synthesis of flagella. The flhDC operon is known as an initiation operon of flagellar regulon. Transcriptional analysis of this operon revealed that its efficient expression is dependent on a nucleoid protein, H-NS. H-NS has been shown to modulate the supercoiling structure of bacterial chromosome. Because dynamic change of the topology of chromosome during DNA replication process can influence the association of H-NS with specific DNA regions, the expression of flagellar regulon and thus the synthesis of flagella may be regulated by DNA replication process through interaction of DNA with H-NS.