Growth and nitrite production by Azospirillum strains subjected to different levels of dissolved oxygen in the medium

Azospirillum growth responses to temperature and the capacity of NO3−-grown bacteria to produce nitrite, were investigated in three southern Brazilian isolated strains exposed to various concentrations of dissolved oxygen in the medium. The strains Azospirillum brasilense Sp245 and JA04, and A. lipoferum JA03, responded differently to incubation temperature, strain JA03 showing more active growth at the lowest temperature, 28°C, while strains Sp245 and JA04 greater cell multiplication at 32 and 37°C. The exposure of bacteria to different amounts of oxygen dissolved in the medium permitted discrimination of the three strains with respect to growth and nitrite production. Strain JA03 showed remarkably high nitrite accumulation and more intense growth at the lowest oxygen tensions compared with strains Sp245 and JA04. It is conceivable that the highest growth measured in strain JA03 under semi-anaerobic conditions was partly due to efficient utilization of nitrate in respiration. Our data for Azospirillum suggest that the capacity of strain JA03 to withstand reduced oxygen concentrations and relatively lower temperature conditions during growth might be identified as favorable adaptive attributes leading to better acclimation to water-logged and highly compacted sub-tropical soils.