Strain UCT61a showed a slightly lower tolerance to streptomycin (about 0.6 – 0.8 μg ml-1) but exhibited a higher tolerance of spectinomycin (about 10.0 selleck products – 20.0 μg ml-1). Strains UCT40a and PPRICI3, on the other hand, were highly sensitive to low concentrations of the two antibiotics, with resistance to 0.1 – 0.2 μg ml-1 streptomycin and 0.4 – 0.8 μg ml-1 spectinomycin. Figure 1 Intrinsic natural resistance of Cyclopia rhizobial strains to low concentrations of streptomycin sulphate (A) and spectinomycin dihydrochloride pentahydrate (B). Values are mean colony-forming units (CFU) per plate (n = 3 and error bars represent standard errors). Selleck NSC 683864 Nodulation and competitive ability of antibiotically-marked versus unmarked strains The uninoculated control plants were not nodulated and thus showed significantly lower plant dry matter yield compared to the inoculated (nodulated) seedlings (P < 0.01, Table 2). The nodulation and N2-fixing ability of the mutants of strains PPRICI3, UCT44b and UCT61a were not altered by the antibiotic marker, as there were no significant differences in plant biomass, nodule mass or nodule number between strains (P < 0.05, Table 2). Marked strain UCT40a Mkd3 produced no nodules, thus showing

loss of symbiotic ability. Mutant strains UCT40a Mkd1 and UCT40a Mkd2 however showed no loss of their nodulation capacity compared to their parent strain (Table 2). Table 2 Nitrogen-fixing ability of marked rhizobial strains. Treatment Total dry weight (mg) Nodule biomass (mg) Nodule number Uninoculated 0.06 ± 0.04 a 0.00 ± 0.00 a 0.0 ± 0.0 a Inoculated 0.72 ± 0.01 b 33.33 ± 0.07 b 19.6 ± 0.1 b t (1,83) 2.58 ** 2.60 ** 3.49 ** PPRICI3 Parent 0.87 ± 0.13 18.60 ± 0.64 14.8 ± 0.5 PPRICI3Mkd1 0.70 ± 0.14 23.60 ± 0.78 13.2 ± 0.7 PPRICI3Mkd2 0.68 ± 0.10 15.40 ± 0.48 11.2 ± 0.5 PPRICI3Mkd3 1.26 ± 0.13 18.00 ± 0.62 12.6 ± 0.5 F (3,16) 2.06 ns 0.51 ns

0.17 ns UCT40a Parent 2.26 ± 0.19 a 75.76 ± 1.36 a 20.0 ± 0.7 a UCT40aMkd1 1.83 ± 0.23 a 74.70 ± 1.38 a 24.3 ± 0.7 a UCT40aMkd2 2.13 ± 0.20 a 81.94 Levetiracetam ± 1.20 a 31.6 ± 0.7 a UCT40aMkd3 0.12 ± 0.06 b 0.00 ± 0.00 b 0.0 ± 0.0 b F (3,16) 4.35 * 10.30 ** 8.13 ** UCT44b Parent 0.37 ± 0.13 31.25 ± 0.43 18.0 ± 0.4 UCT44bMkd1 0.90 ± 0.12 56.00 ± 0.81 33.4 ± 0.8 UCT44bMkd2 0.51 ± 0.09 23.20 ± 0.47 18.4 ± 0.5 click here UCT44bMkd3 0.66 ± 0.12 25.60 ± 0.60 18.2 ± 0.6 F (3,16) 1.61 ns 2.22 ns 2.94 ns UCT61a Parent 0.84 ± 0.12 39.82 ± 0.93 25.4 ± 0.7 UCT61aMkd1 0.54 ± 0.09 22.64 ± 0.44 16.0 ± 0.5 UCT61aMkd2 0.61 ± 0.10 34.02 ± 0.73 21.6 ± 0.5 UCT61aMkd3 1.07 ± 0.14 48.10 ± 1.04 32.0 ± 0.8 F (3,16) 2.79 ns 1.63 ns 1.79 ns Values are mean ± SE (n = 5) and different letters within a column indicate significant differences.