Differential expression of nonagglutinating fimbriae and MR P pili in swarming colonies of Proteus mirabilis

The expression of nonagglutinating fimbriae (NAF) and mannose-resistant/Pro teus-like (MR/P) pill in swarming colonies of Proteus mirabilis was investi gated. Elongated swarmer cells do not express pill, and the relative number of bacteria expressing NAF during swarming and early consolidation phases was very low (<5%). Relative expression of NAF in a terrace increased to ap proximately 30% at 48 h. We also determined the expression of NAF and MR/P pill in two phenotypically distinguishable regions of each terrace. The exp ression of both NAF and MR/P pill was always higher in the region closer (p roximal) to the middle of the colony than in the distal region of the terra ce. The relative numbers of bacteria expressing NAF or MR/P pill in the pro ximal region were between 39.1 and 63% and between 5.9 and 7.7%, respective ly. In the distal region, expression levels were between 20.8 and 27.3% and between 3.7 and 5.6%, respectively, A time course experiment testing NAF e xpression in both the proximal and distal regions of a terrace indicated th at NAF expression in the proximal regions was always higher than in the dis tal regions and increased to a plateau 40 to 50 h after the start of the sw arming phase for any given terrace. These results indicate that expression of NAF or MR/P pill in swarming colonies of P. mirabilis is highly organize d, spatially and temporally, The significance of this controlled differenti ation remains to be uncovered.