Open AccessCharacterization of Tn 5 ‐induced symbiotically defective mutants of cowpea rhizobia
Author(s) -
McLaughlin Wayne,
Singh Inderpal,
Ahmad M.H.
Publication year - 1987
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1987.tb02222.x
Subject(s) - rhizobia , biology , mutant , vigna , auxotrophy , transposon mutagenesis , mutagenesis , root hair , rhizobium , rhizobiaceae , leghemoglobin , transposable element , root nodule , biochemistry , genetics , botany , symbiosis , gene , bacteria
Symbiotically defective mutants of cowpea rhizobia strain IRC256 were isolated by random Tn 5 mutagenesis and characterized. One auxotroph (MS1) requiring adenine and thiamine was a non‐nodulating mutant (Nod − ) and three prototrophic mutants were Nod + Fix − which formed small and ineffective nodules on cowpeas ( Vigna unguiculata ). Acetylene reduction activity of the Nod + Fix − mutants was reduced to 80–94% of that of the wild‐type strain. The non‐nodulating mutant (MS1) induced root‐hair curling but did not show any nodule initiation or nodule development. Ultrastructural examination of nodules formed by Fix − mutants showed that these contained few bacteroids, indicating either early senescence or a reduction in bacterial release into the cytoplasm of the host cell. DNA hybridization of total DNAs from a representative number of Tn 5 mutants showed that each of them had one copy of the transposon Tn 5 which was randomly inserted into the genome of cowpea rhizobia.