Bacterial delta-aminolevulinic acid synthase activity is not essential for leghemoglobin formation in the soybean/Bradyrhizobium japonicum symbiosis
Previous studies of legume nodules have indicated that formation of the heme moiety of leghemoglobin is a function of the bacterial symbiont. The authors now show that a hemA mutant of Bradyrhizobium japonicum that cannot carry out the first step in heme biosynthesis forms fully effective nodules on soybeans. The bacterial mutant strain was constructed by first isolated the wild-type hemA gene encoding delta-aminolevulinic acid synthase (EC 2.3.1.37) from a cosmid library, using a fragment of the Rhizobium meliloti hemA gene as a hybridization probe. A deletion of the hemA gene region, generated in vitro, then was used to construct the analogous chromosomal mutation by gene-directed mutagenesis. The mutant strain had no delta-aminolevulinic acid synthase activity and was unable to grow in minimal medium unless delta-aminolevulinic acid was added. Despite its auxotrophy, the mutant strain incited nodules that appeared normal, contained heme, and were capable of high levels of acetylene reduction. These results rule out bacterial delta-aminolevulinic acid synthase activity as the exclusive source of delta-aminolevulinic acid for heme formation in soybean nodules.
- Research Organization:
- Michigan State Univ., East Lansing, MI (United States)
- DOE Contract Number:
- AC02-76ER01338
- OSTI ID:
- 5934614
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 83:6
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HEMOGLOBIN
BIOSYNTHESIS
TRANSFERASES
BIOCHEMISTRY
AMINOLEVULINIC ACID
ENZYME ACTIVITY
MUTANTS
NITROGEN FIXATION
RHIZOBIUM
SOYBEANS
SYMBIOSIS
AMINO ACIDS
BACTERIA
CARBOXYLIC ACIDS
CHEMISTRY
ENZYMES
FOOD
GLOBIN
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
MICROORGANISMS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PLANTS
PORPHYRINS
PROTEINS
SYNTHESIS
VEGETABLES
550200* - Biochemistry