Phenotypic characteristics of root-nodulating bacteria isolated from Acacia spp. grown in Libya

Thirty isolates of root-nodulating bacteria obtained from Acacia cyanophyll a, A. karroo, A. cyclops, A. tortilis (subsp.raddiana), Faidherbia albida a nd Acacia sp., grown in different regions of Libya, were studied by perform ing numerical analysis of 104 characteristics. Three fast- and one slow-gro wing reference strains from herbaceous and woody legumes were included. Fiv e distinct clusters were formed. The fast-growing reference strains were se parated from the isolates whereas the slow-growing was included in cluster 4. With the exception of one cluster, the majority of clusters were formed regardless of the host plant or site of origin. Based on plant tests, gener ation times, acid production and carbon utilization the isolates were diver se (fast and slow-growing isolates). Like slow-growing isolates, most of th e fast-growing isolates appeared to be non-specific, nodulated many species from the same genus notably F. albida, known to nodulate only with slow-gr owing strains. Most clusters grew at temperatures 35 degreesC and 37 degree sC; some grew at temperatures above 40 degreesC. The majority of isolates g rew at acid and alkaline pH and only one isolate grew below pH 4. Most isol ates were able to utilize many amino acids as nitrogen sources and to reduc e nitrate. Urea was hydrolysed by all clusters. Monosaccharides and polyols were used by slow and fast-growing isolates as the only carbon sources whe reas assimilation of disaccharides varied: Some isolates, like slow-growing isolates, failed to utilize these carbon sources. Most isolates were unabl e to utilize polysaccharides. Regarding tolerance to NaCl on agar medium, t he majority of isolates were unable to grow at a concentration of 2% NaCl, but some were highly resistant and there was one isolate which grew at 8% N aCl. Most isolates were resistant to heavy metals and to antibiotics.