T. de la Rubia

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 carbon and nitrogen limitation on lignin peroxidase and manganese peroxidaseproduction by Phanerochaete flavido‐alba

The ligninolytic enzymes lignin peroxidase (LiP) and manganese dependent peroxidase(MnP), were detected in extracellular fluids of Phanerochaete flavido‐alba FPL 106507cultures under carbon or nitrogen limitation. MnP activities were found to be higher than LiPactivities under all growth conditions tested. Higher titres of both peroxidases were obtainedunder carbon limitation in excess nitrogen. Isoelectric points (pIs) observed after FPLC and IEFof concentrated extracellular fluids revealed more acidic pIs for LiP enzymes obtained innitrogen‐limited cultures than those in carbon‐limited cultures. However, the change in thelimiting growth factor does not significantly affect MnP pIs.

Phanerochaete flavido-alba ligninolytic activities and decolorization of partially bio-depurated paper mill wastes

Among 12 basidiomycetaceous fungal strains, Phanerochaete chrysosporium SC26 and K3 and Phanerochaete flavido-alba FPL 106507 were the most efficient in decolorizing paper mill wastes. Enzymatic activities attributable to both families of extracellular ligninases, lignin peroxidase (LiP) and manganese peroxidase (MnP), have been detected in P. flavido-alba FPL 106507. Both peroxidase activities seem to be implicated in the decolorization of partially bio-depurated paper mill waste waters, but LiP activity seems to play a more important role.

Effect of phanerochaete flavido‐alba on aromatic acids in olive oil mill waste waters

Phanerochaete flavido‐alba was an effective organism for transforming the aromatic mixture of olive oil mill waste water phenolics. Mono and dimethoxylated phenolic acids were efficiently transformed but 3,4,5‐trimethoxybenzoic acid was not. Ligninolytic peroxidase induced cultures were more efficient as aromatic degraders than nitrogen repressed ones and lignin peroxidase (LiP) induced cultures were more effective as degraders than manganese peroxidase (MnP) induced cultures. In spite of this finding, lignin peroxidase concentrated extracellular fluid showed a negligible effect on degradation, suggesting the implication of “de novo” synthesized proteins and not only ligninolytic peroxidases in the transformation detected.

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.

Growth and nitrogenase activity of Azotobacter vinelandii in the presence of several phenolic acids

Growth and nitrogenase activity (acetylene reduction) of Azotobacter vinelandii in chemically defined N-free media were studied in the presence of p-hydroxybenzoic, vanillic, p-coumaric, and ferulic acids at concentrations from 0.01 to 1% (w/v). Growth and nitrogenase activity were only detected when the microorganism was cultured on p-hydroxybenzoic acid either as sole carbon source or mixed with other phenolic acids, suggesting that p-hydroxybenzoic acid could be utilized as a carbon source by A. vinelandii for growing under certain environmental conditions.

Growth of Bacillus megaterium in phosphate-limited medium

Bateh cultures ofBacillus megaterium grown in phosphate-limited media were compared with control cultures grown in phosphate-sufficient media. The effects of phosphate limitation on growth were determined by viable cells counts. Intracellular levels of protein, RNA, poly-3-hydroxybutyrate, carbohydrate and oxygen uptake were significantly affected by phosphate limitation. Electron micrographs of sectioned cells revealed differenees in the structure; in particular the thick, rigid cell wall was absent from cells grown in phosphate-limited media, and such eells were larger, pleomorphic, and after 2 d were insensitive to lysczyme.