A novel p(H2) control on the expression of flagella in the hyperthermophilic strictly hydrogenotrophic methanarchaeaon Methanococcus jannaschii

The methanarchaeon. Methanococcus jannaschii, a hyperthermophilic, autotrop hic. and strictly hydrogenotrophic inhabitant of submarine hydrothermal ven ts, was cultivated in a reactor at two hydrogen partial pressure (pH(2)) va lues. 178 kPa (high) and 650 Pa (ultralow), and the cells were subjected to a comparative proteome analysis. From these studies, it was discovered tha t, when pH(2) was high and the cell density was low (a combination represen ting a hydrogen-excess condition), the cells possessed very low or undetect able levels of four flagella-related polypeptides (FlaB2, FlaB3, FlaD, and FlaE); electron microscopic examination showed that most of these cells wer e devoid of flagella. Flagella synthesis occurred when hydrogen became limi ting either at high cell density under high pH(2) or at low cell density un der low PH2. The results from a pH(2)-shift experiment corroborated the abo ve observations. The pH(2)-dependent changes in the levels of two methanoge nic enzymes (MTD and HMDX) were as expected, and thus they served as intern al controls. To our knowledge, this is the first example for the regulation of expression of flagella by hydrogen in any domain of life and for a cont rol of any kind on flagella synthesis in the archaea. Our work also provide s the only known example for each of the following: (i) the pure culture cu ltivation of a methanogen at an ultralow, near ecologically relevant p(H2); (ii) experimental functional genomics for M. jannaschii; and (iii) the use of proteomics with M, jannaschii.