Rhizobium sullae, formerly Rhizobium ’hedysari’, is a nitrogen fixing bacterium that induces symbiotic nodule formation on the legume Hedysarum coronarium. Some isolates belonging to this species have been shown to encode a copper-containing nitrite reductase, encoded by nirK, which is closely related to nitrite reductases in true denitrifiers. Nitrite reductase reduces nitrite to nitric oxide (NO). Nir activity in the HCNT1 strain is induced under low oxygen and results in accumulation of toxic levels of NO if nitrite is present. Therefore, HCNT1 cannot grow as a denitrifier. Inactivation of nirK resulted in no obvious phenotypic changes other than those linked to the loss of NO production (Toffanin et al, 1996) Strains of the same species that lack Nir (e.g. strain CC1335) can nodulate and fix nitrogen at the same level so the function of Nir in HCNT1 is unclear. Recent investigations showed that strain HCNT1, as well as other bacteria including different species of rhizobia, can enter the so-called VBNC (Viable But Not Culturable) state (Toffanin et al., 2000) when oxygen is limiting and nitrite is converted to NO. Such a metabolic state confers to the cells the ability to withstand stresses, including antibiotic effects or nutrient depletion; when suitable environmental conditions resume, it has been demonstrated that some VBNC bacterial populations can recover their culturability (Casella et al, 2001). In order to verify the hypothesis that expression of nirK is favourable because it induces the VBNC state, nirK from HCNT1 has been mobilized into CC1335 and the resulting phenotype studied. In related work the occurrence of genes encoding NO reductase in various R. sullae strains has been examined by a PCR-based approach. This was done to determine if the NO accumulation phenotype is due to loss of genes encoding NO reductase.

Elucidating the cause and effect of NO accumulation in R. sullae Strain HCNT1

BASAGLIA, MARINA;BALDAN, ENRICO;CASELLA, SERGIO
2004

Abstract

Rhizobium sullae, formerly Rhizobium ’hedysari’, is a nitrogen fixing bacterium that induces symbiotic nodule formation on the legume Hedysarum coronarium. Some isolates belonging to this species have been shown to encode a copper-containing nitrite reductase, encoded by nirK, which is closely related to nitrite reductases in true denitrifiers. Nitrite reductase reduces nitrite to nitric oxide (NO). Nir activity in the HCNT1 strain is induced under low oxygen and results in accumulation of toxic levels of NO if nitrite is present. Therefore, HCNT1 cannot grow as a denitrifier. Inactivation of nirK resulted in no obvious phenotypic changes other than those linked to the loss of NO production (Toffanin et al, 1996) Strains of the same species that lack Nir (e.g. strain CC1335) can nodulate and fix nitrogen at the same level so the function of Nir in HCNT1 is unclear. Recent investigations showed that strain HCNT1, as well as other bacteria including different species of rhizobia, can enter the so-called VBNC (Viable But Not Culturable) state (Toffanin et al., 2000) when oxygen is limiting and nitrite is converted to NO. Such a metabolic state confers to the cells the ability to withstand stresses, including antibiotic effects or nutrient depletion; when suitable environmental conditions resume, it has been demonstrated that some VBNC bacterial populations can recover their culturability (Casella et al, 2001). In order to verify the hypothesis that expression of nirK is favourable because it induces the VBNC state, nirK from HCNT1 has been mobilized into CC1335 and the resulting phenotype studied. In related work the occurrence of genes encoding NO reductase in various R. sullae strains has been examined by a PCR-based approach. This was done to determine if the NO accumulation phenotype is due to loss of genes encoding NO reductase.
2004
Cost Action 856- Ecological aspects of denitrification, with emphasis on agriculture
Cost Action 856- Ecological aspects of denitrification, with emphasis on agriculture
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2447682
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