DIFFERENTIATION OF CLOVER RHIZOBIUM ISOLATED FROM BIOSOLIDS-AMENDED SOILS WITH VARYING PH

Metal contamination may alter the diversity of microbes residing in so il, The genetic structure and phenotypic characteristics of clover Rhi zobium isolated from contaminated and control soils were compared. Pla nt infection and symbiotic competence tests were used for phenotypic c haracterization. Variation across isolates in fingerprint patterns det ermined with primers for repetitive extragenic palindromic (REP) seque nces and the polymerase chain reaction (PCR) were used for genetic cha racterization. Two phenotypic groups of effective and ineffective isol ates were identified using the symbiotic effectiveness test, Soil pH w as the primary factor influencing this phenotypic characteristic, Effe ctive isolates were associated with higher soil pH and ineffective iso lates were associated with lower soil pH regardless of soil metal cont ent. The isolates were genetically diverse. The variation of isolates from the different soils overlapped, indicating that neither the heavy metals nor the low soil pH resulted in the selection of a single geno type, Isolates from the most heavily contaminated soils were more vari able than isolates from control soils, Soil pH, and not heavy metal co ntent, was important in the selection of rhizobia that formed ineffect ive N-2-fixing symbioses.