Determination of the hydrogenase status of individual legume nodules by a methylene blue reduction assay.
We adapted a method for the rapid screening of colonies of free-living Rhizobium japonicum for hydrogenase activity to determine the hydrogenase status of individual soybean nodules. Crude bacteroid suspensions from nodules containing strains known to be hydrogen uptake positive (Hup) caused a localized decolorization of filter paper disks, whereas suspensions from nodules arising from inoculation with hydrogen uptake-negative (Hup) mutants or strains did not decolorize the disks. The reliability of the method was demonstrated by its successful application to 29 slow-growing rhizobia. The Hup phenotype on methylene blue filters agreed with that determined amperometrically with either methylene blue or oxygen as the electron acceptor.
Lambert
G R
GR
Laboratory for Nitrogen Fixation Research, Oregon State University, Corvallis, Oregon 97331.
Hanus
F J
FJ
Russell
S A
SA
Evans
H J
HJ