Denitrification activity of phage types representative of two populations of indigenous Rhizobium meliloti

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Abstract
Isolates of Rhizobium meliloti from indigenous populations at two sites were previously characterized according to phage sensitivity. Isolates representative of the 55 and 65 phage types comprising these two populations, respectively, were tested for denitrification activity with nitrate or nitrite as substrate. Fifty-seven of 120 isolates were capable of denitrification with activities varying considerably between phage types. Only one isolate was able to denitrify nitrite but not nitrate, indicating the presence of a truncated denitrification pathway. Each of five phage types showed variation in denitrification ability between isolates from different sites, indicating possible adaptation of indigenous R. meliloti to their respective environments. The estimated frequency of occurrence of denitrifiers in the two indigenous populations of R. meliloti (9 and 13%) differed significantly between sites with and without a previous history of Medicago sativa cultivation, respectively.Key words: Rhizobium, denitrification, populations, phage.