Diffusion of related NirK and oxyanions reduction activities in soil microorganisms

Recent studies suggest a relation between the capacity of Rhizobium sullae HCNT1 to reduce selenite and its ability to reduce nitrite to nitric oxide, due to the presence of a copper nitrite reductase encoded by nirK. In fact, in R. sullae HCNT1 the reduction of selenite has been found to be completely dependent on the presence of nirK, while nirK derivatives afe not able to reduce selenite. Considering that other R. sullae strains that were collected in the same region where HCNT1 was originally isolated show the same behaviour, the present work was undertaken to determine if other soil microorganisms share this capacity. To do this, bacteria from collections or new isolates from potentially relevant environments were characterized to determine if other bacteria bave nirK dependent selenite reductases activity. This was done by screening for the presence of nirK, eventually far Nir activity and far the capacity to grow in the presence and/or reduce selenite. Rhizobium, Acinetobacter, Pseudomonas, Azospirillum and Bacillus species were assayed in the presence of selenite at concentration between 5 and 100 mM. The results confirm that the ability to reduce selenite is not a common trait in soil microorganisms. The presence of nirK, assessed by PCR, was infrequent in the microorganisms that were studied. Interestingly, nirK was found in a couple of Rhizobium strains isolated.from metal rich soils from Italy