Selection for acid tolerance inRhizobium meliloti

Abstract

In the selection of acid-tolerant Rh&obium meliloti, procedures for the collection and isolation of rhizobia, and the assessment of acid tolerance, have not been critically evaluated. Such procedures form the basis of this study. Root nodules were collected from Medicago spp. found growing on acid soil in Sardinia. Their encumbent bacteria were isolated directly onto media adjusted over a range ofpH values, and then assessed for acid tolerance in both the laboratory and field. Strains of Rh&obium meliloti isolated onto low pH media were, in general, more acid-tolerant than sister isolates from high pH media, when tested in both the laboratory and field. Dilution (10 or 100 fold) of the inocula used in the laboratory assessment did not greatly influence the rating derived, although there was some effect of bacterial colony type on growth rating. The link between polysaccharide production and acid tolerance was not strong. There was a poor correlation between the growth ratings derived from the laboratory screening and acid tolerance as expressed in the field.

Novel Burkholderia bacteria isolated from Lebeckia ambigua – A perennial suffrutescent legume of the fynbos

“…Nodulating Burkholderia strains have previously been noted as micro-organisms adapted to acid and infertile soils (Garau et al, 2009;Gyaneshwar et al, 2011). However, growth on acidified media is not always indicative of success in acid soil, and edaphic evaluation must be conducted in situ (Howieson et al, 1988).…”

Enhanced nodulation and symbiotic effectiveness of Medicago truncatula when co-inoculated with Pseudomonas fluorescens WSM3457 and Ensifer (Sinorhizobium) medicae WSM419

“…Both strains were sourced from the Western Soil Microbiology (WSM) collection held at the Centre for Rhizobium Studies at Murdoch University. E. medicae WSM419 was cultured using ½ LA medium (Howieson et al 1988) and WSM3457 was cultured in Nutrient Broth (Difco). For solid media the broth was supplemented with 1.5% (w/v) agar.…”

Survival and exopolysaccharide production in Sinorhizobium meliloti WSM419 are affected by calcium and low pH

“…Acid-tolerant strains of Sinorbizobiurn meliloti like WSM419 have subsequently been isolated from acidic soils in the Mediterranean (Howieson & Ewing, 1986), leading to the successful establishment of medic pastures on acid soils in Western Australia (Howieson et al, 1988(Howieson et al, , 1991.…”