D. Purchase et al., CADMIUM UPTAKE AND NITROGEN-FIXING ABILITY IN HEAVY-METAL-RESISTANT LABORATORY AND FIELD STRAINS OF RHIZOBIUM-LEGUMINOSARUM BIOVAR TRIFOLII, FEMS microbiology, ecology, 22(1), 1997, pp. 85-93
Rhizobium leguminosarum bv. trifolii produced mucoid colonies on yeast
mannitol agar, but non-mucoid colonies appeared with a frequency of 1
0(-7) on agar additionally containing 4 mM ZnCl2. Cells producing non-
mucoid colonies were also obtained from root nodules of white clover f
rom experimental field plots treated with heavy-metal-contaminated sew
age sludge. Compared to mucoid strains, non-mucoid strains produced ap
proximately half of the extracellular polysaccharide, two to three fol
d higher levels of intracellular carbohydrate and possessed larger int
racellular inclusions. They also showed up to two-fold times greater r
esistance to Cd2+, Cu2+, Ni2+ and Zn2+. The total uptakes of Cd2+ were
similar between the laboratory strains and amongst the field strains.
In non-mucoid strains, Cd2+ was not removed by washing in 0.1 M HNO3,
suggesting Cd2+ was bound intracellularly. All strains were effective
in fixing nitrogen in white clover.