Response of the Endophytic Diazotroph Gluconacetobacter diazotrophicus on Solid Media to Changes in Atmospheric Partial O2 Pressure

AUTOR(ES)

Pan, Bo

FONTE

American Society for Microbiology

RESUMO

Gluconacetobacter diazotrophicus is an N2-fixing endophyte isolated from sugarcane. G. diazotrophicus was grown on solid medium at atmospheric partial O2 pressures (pO2) of 10, 20, and 30 kPa for 5 to 6 days. Using a flowthrough gas exchange system, nitrogenase activity and respiration rate were then measured at a range of atmospheric pO2 (5 to 60 kPa). Nitrogenase activity was measured by H2 evolution in N2-O2 and in Ar-O2, and respiration rate was measured by CO2 evolution in N2-O2. To validate the use of H2 production as an assay for nitrogenase activity, a non-N2-fixing (Nif−) mutant of G. diazotrophicus was tested and found to have a low rate of uptake hydrogenase (Hup+) activity (0.016 ±  0.009 μmol of H2 1010 cells−1 h−1) when incubated in an atmosphere enriched in H2. However, Hup+ activity was not detectable under the normal assay conditions used in our experiments. G. diazotrophicus fixed nitrogen at all atmospheric pO2 tested. However, when the assay atmospheric pO2 was below the level at which the colonies had been grown, nitrogenase activity was decreased. Optimal atmospheric pO2 for nitrogenase activity was 0 to 20 kPa above the pO2 at which the bacteria had been grown. As atmospheric pO2 was increased in 10-kPa steps to the highest levels (40 to 60 kPa), nitrogenase activity decreased in a stepwise manner. Despite the decrease in nitrogenase activity as atmospheric pO2 was increased, respiration rate increased marginally. A large single-step increase in atmospheric pO2 from 20 to 60 kPa caused a rapid 84% decrease in nitrogenase activity. However, upon returning to 20 kPa of O2, 80% of nitrogenase activity was recovered within 10 min, indicating a “switch-off/switch-on” O2 protection mechanism of nitrogenase activity. Our study demonstrates that colonies of G. diazotrophicus can fix N2 at a wide range of atmospheric pO2 and can adapt to maintain nitrogenase activity in response to both long-term and short-term changes in atmospheric pO2.

Documentos Relacionados

• Effects of Partial O2 Pressure, Partial CO2 Pressure, and Agitation on Growth Kinetics of Azospirillum lipoferum under Fermentor Conditions
• The Regulation of Rubisco Activity in Response to Variation in Temperature and Atmospheric CO2 Partial Pressure in Sweet Potato1[w]
• The Resistance of the Diffusion Barrier in Nodules of Myrica gale L. Changes in Response to Temperature but Not to Partial Pressure of O2.
• Photosynthetic Acclimation in Pea and Soybean to High Atmospheric CO2 Partial Pressure.
• Economic feasibility of Gluconacetobacter diazotrophicus in carrot cultivation