Detection of uptake hydrogenase in Rhizobium leguminosarum and Rhizobium meliloti

Summary A rapid colour test is described which is selective for uptake hydrogenase (Hup+) activity under ex planta conditions. The test is based on decolonization of methylene blue. The decolonization time is a function of Hup activity. It is possible to select single colonies showing different Hup activities. A known Hup+ strain of R. leguminosarum is found to contain bacteria with both high and low Hup activities, respectively. The Hup phenotype of a given strain consequently represents a mean value determined by the proportion of cells with different Hup activities. Hup activity in R. leguminosarum was shown to vary under ex planta conditions and during symbiosis. It is shown that by selection for single colonies it is possible to obtain R. meliloti strain of enhanced uptake hydrogenase activity.