Rhizobium sullae is an unusual and unique bacterium due to the radical truncation of its denitrification electron transport chain. This bacterium has only one of the four terminal reductases required for complete denitrification. The sole reductase present, nitrite reductase, produces a toxic end product, nitric oxide. This enzyme cannot be used to support growth under anoxic conditions. Expression of the gene encoding nitrite reductase, nirK, is also unusual in that it does not require the presence of a nitrogen oxide. Expression only requires a decrease in oxygen concentration. The role of nitrite reductase in R. sullae has yet to be elucidated. The presence and expression of nitrite reductase has been investigated as a detoxification strategy or as a means to reduce the energy content in the bacterial cell in order to induce dormancy. Since nitrite reductase expression only occurs under microoxic conditions it is possible the enzyme plays some role within the root nodule, which is a low oxygen environment. However, comparisons of nodulation efficiency, plant growth and nitrogen fixation have not revealed any significant differences between wild type and nitrite reductase-deficient strains, so far. Some evidence has been provided suggesting a link between nitrite reductase activity and the viability and culturability of the cells. Nitrite reductase activity may reduce energy content but it remains uncertain whether this is an indirect consequence of generation of nitric oxide or a desired result intended to prolong cell viability under certain conditions. Recently, several bacterial species have been found to contain reductases with the capacity to reduce multiple oxyanions. The oxyanion reducing capacity activity of the copper-containing nitrite reductase of R. sullae was tested to determine its substrate range. In addition, the oxyanion-reducing capacity of several nirK-plus and nirK-minus strains of R. sullae was compared with that of other denitrifying and non-denitrifying bacterial strains belonging to the genera Stenotrophomonas, Bacillus, Agrobacterium and Rhodobacter. The results suggest that the nitrite reductase of R. sullae can reduce other physiologically important oxyanions, which may provide new insight into the role of this enzyme.

Multiple oxyanion reducing capacity of the copper-containing nitrite reductase of R. sullae

BASAGLIA, MARINA;BALDAN, ENRICO;CASELLA, SERGIO
2005

Abstract

Rhizobium sullae is an unusual and unique bacterium due to the radical truncation of its denitrification electron transport chain. This bacterium has only one of the four terminal reductases required for complete denitrification. The sole reductase present, nitrite reductase, produces a toxic end product, nitric oxide. This enzyme cannot be used to support growth under anoxic conditions. Expression of the gene encoding nitrite reductase, nirK, is also unusual in that it does not require the presence of a nitrogen oxide. Expression only requires a decrease in oxygen concentration. The role of nitrite reductase in R. sullae has yet to be elucidated. The presence and expression of nitrite reductase has been investigated as a detoxification strategy or as a means to reduce the energy content in the bacterial cell in order to induce dormancy. Since nitrite reductase expression only occurs under microoxic conditions it is possible the enzyme plays some role within the root nodule, which is a low oxygen environment. However, comparisons of nodulation efficiency, plant growth and nitrogen fixation have not revealed any significant differences between wild type and nitrite reductase-deficient strains, so far. Some evidence has been provided suggesting a link between nitrite reductase activity and the viability and culturability of the cells. Nitrite reductase activity may reduce energy content but it remains uncertain whether this is an indirect consequence of generation of nitric oxide or a desired result intended to prolong cell viability under certain conditions. Recently, several bacterial species have been found to contain reductases with the capacity to reduce multiple oxyanions. The oxyanion reducing capacity activity of the copper-containing nitrite reductase of R. sullae was tested to determine its substrate range. In addition, the oxyanion-reducing capacity of several nirK-plus and nirK-minus strains of R. sullae was compared with that of other denitrifying and non-denitrifying bacterial strains belonging to the genera Stenotrophomonas, Bacillus, Agrobacterium and Rhodobacter. The results suggest that the nitrite reductase of R. sullae can reduce other physiologically important oxyanions, which may provide new insight into the role of this enzyme.
2005
COST meeting, 11th Nitrogen Cycle Meeting
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2447807
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