J. Moreno

Effect of inoculation with Azotobacter chroococcum on nitrogenase activity of Zea mays roots grown in agricultural soils under aseptic and non-sterile conditions

SummaryInoculated and non-inoculated seedlings of Zea mays were grown in agricultural soils under aseptic and non-sterile conditions. Acetylene reduction activity and microbial counts were determined after 7 and 30 days of growth. Irrespective of the soil type Azotobacter spp. were commonly isolated under maize cultivation. Inoculation of agricultural soils with a suspension of A. chroococcum led to an increase in Azotobacter numbers, although this effect diminished with time. Nitrogenase activity was detected on maize roots and increased in response to the inoculation with A. chroococcum, showing that this associative growth could be of primary importance for the plant. The results of assays for acetylene reduction activity indicated that the nitrogenase activity was associated only with the root systems.

Root exudates ofZea mays and production of auxins, gibberellins and cytokinins byAzotobacter chroococcum

Growth ofAzotobacter chroococcum in N-free medium was stimulated in the presence of maize root exudates. Our results show that the production of auxins, gibberellins and cytokinins were significantly stimulated when maize root exudates from 7 to 30 d old plants were added to the culture media.

Effect of diflubenzuron on Azotobacter nitrogen fixation in soil

The effect of 100, 200, 300, 400 and 500 μg diflubenzuron per gram of soil was studied in nonsterile soil incubated under aerobic conditions, and in sterilized soil inoculated with Azotobacter vinelandii. The presence of 100 to 500 μg/g had a stimulatory effect on dinitrogen fixation in both nonsterile and sterile soil.

Adenine nucleotide contents and energy charge of Azotobacter vinelandii grown at low phosphate concentration

The effect of a low phosphate concentration on intracellular adenine nucleotide content, oxygen consumption and poly-β-hydroxybutyrate deposition was investigated with N-free and NH4+batch cultures of Azotobacter vinelandii. When the microorganisms were cultured under low-phosphate concentrations the cells contained much larger amounts of poly-β-hydroxybutyrate, but displayed lower oxygen consumption activities and energy charge values than did control cells. Also, the ratio ATP to ADP was much higher in control cells and the intracellular levels of ATP were lower in low-phosphate cells.

Grain yield response of Zea mays (hybrid AE 703) to Azotobacter chroococcum H23

SummaryField experiments were conducted during 1985 and 1986 to examine the effect of Azotobacter chroococcum on the grain yield of maize. Application of 40 kg N ha−1 plus A. chroococcum caused a significant increase in maize yield. Azotobacter inoculation was more efficient at lower doses (40 kg N ha−1) than at high doses (80 kg N ha−1) of urea.

Effect of 2,3,6-TBA on Azotobacter nitrogen fixation in soil

Abstract The effect of 100, 200, 300, 400 and 500 μg 2,3,6-trichlorobenzoic acid (2,3,6-TBA) per gram soil, was studied in nonsterile soil incubated under aerobic conditions, and in sterilized soil inoculated with Azotobacter vinelandii . 2,3,6-TBA at a concentration of 200 μg/g had an inhibitory effect in nonsterile soil while strong inhibition of dinitrogen fixation in sterile soil occurred in the presence of 100 μg/g and above.

Growth of Azotobacter vinelandii in dialysed soil medium: Studies upon the life cycle

Azotobacter vinelandii ATCC 12837 cultured in dialysed soil medium with addition of 0.5% glucose showed four distinct morphological cell types: large cells, precyst forms, mature cysts and filterable corpuscles (0.3 micron in diameter). These results indicate that Azotobacter is a bacterium with a complex life cycle under certain culture conditions. Intracellular levels of RNA and poly-beta-hydroxybutyric acid were significantly affected when cells grown in dialysed soil were compared with those obtained after growth on defined medium (N-free). Further studies showed that the chemical composition of filterable corpuscles obtained from dialysed soil medium were different from the composition of normal Azotobacter cells produced in both culture media (dialysed soil and defined media). We suggest that filterable corpuscles represent a stage in the life cycle of Azotobacter in their natural environment.

Toxicity of dicamba (2-methoxy-3,6-dichlorobenzoic acid) toAzotobacter vinelandii

The effect of dicamba was studied in N-free medium inoculated withAzotobacter vinelandii ATCC 12837. Nitrogen fixation was determined by acetylene reduction. Dicamba at a concentration of 500 μg/mL had a strong inhibitory effect on nitrogenase activity. However, no inhibitory effect on microbial respiration was detected.

Photoreactivation in vegetative cells of Azotobactervinelandii grown in chemically defined media and soil media

Abstract Vegetative cells of Azotobacter vinelandii grown in chemically-defined media and dialysed-soil media were reactivated by white light after inactivation by ultraviolet radiation. When A. vinelandii was grown in dialysed-soil media (similar to their natural habitat) showed a photoreactivating enzyme with a greater activity than the same organism grown in chemically-defined media.