A novel pH2 control on the expression of flagella in the hyperthermophilic strictly hydrogenotrophic methanarchaeaon Methanococcus jannaschii

The methanarchaeon. Methanococcus jannaschii, a hyperthermophilic, autotrophic. and strictly hydrogenotrophic inhabitant of submarine hydrothermal vents, was cultivated in a reactor at two hydrogen partial pressure (pH(2)) values. 178 kPa (high) and 650 Pa (ultralow), and the cells were subjected to a comparative proteome analysis. From these studies, it was discovered that, when pH(2) was high and the cell density was low (a combination representing a hydrogen-excess condition), the cells possessed very low or undetectable levels of four flagella-related polypeptides (FlaB2, FlaB3, FlaD, and FlaE); electron microscopic examination showed that most of these cells were devoid of flagella. Flagella synthesis occurred when hydrogen became limiting either at high cell density under high pH(2) or at low cell density under low PH2. The results from a pH(2)-shift experiment corroborated the above observations. The pH(2)-dependent changes in the levels of two methanogenic enzymes (MTD and HMDX) were as expected, and thus they served as internal 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 control of any kind on flagella synthesis in the archaea. Our work also provides the only known example for each of the following: (i) the pure culture cultivation 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.