V. Salmeron

Effects of the fungicide Captan on some functional groups of soil microflora

Abstract The effects of Captan at rates of 2.0, 3.5, 5.0 and 10.0 kg ha−1 on microbial function were studied in four agricultural soils under aerobic conditions. Parameters monitored included total culturable populations, numbers of aerobic N2-fixing bacteria, denitrifying bacteria, nitrifying bacteria and nitrogenase activity. Total culturable fungal populations, nitrifying bacteria, aerobic N2-fixing bacteria and nitrogenase activity were significantly decreased at dose rates of 2.0 to 10.0 kg ha−1. However, the presence of Captan enhanced denitrifying and total culturable bacteria, showing that some microbial groups can tolerate high doses of this fungicide.

Production of vitamins by Azospirillum brasilense in chemically-defined media

The production of vitamins by Azospirillum brasilense was studied in chemically-defined media amended with malate, gluconate and fructose. The liberation of vitamins was significantly affected by the presence of different carbon sources and the age of the culture. Thiamine, niacin and pantothenic acid were produced in large amounts. Thiamine and riboflavin were produced only in culture containing malate or fructose. Biotin was not detected in the supernatants of the culture media.

Influence of Rhizobium/Azotobacter and Rhizobium/Azospirillum combined inoculation on mineral composition of faba bean (Vicia faba L.)

Abstract Mixed inoculation of Vicia faba L. with four different Rhizobium/Azospirillum and Rhizobium/Azotobacter combinations led to changes in total content, concentration and/or distribution of the mineral macro- and micronutrients, K, P, Ca, Mg, Fe, B, Mn, Zn and Cu, when compared with plants inoculated with Rhizobium only. The effects varied to a great extent among the Azotobacter and Azospirillum strains selected for combined inoculation.

Effect of an organophosphorus insecticide, profenofos, on agricultural soil microflora

Abstract A study was made of the effects of insecticide profenofos at concentrations of 10, 50, 100, 200 and 300 μg per gram of soil on total bacteria populations, fungi, dinitrogen fixer, denitrifying bacteria, nitrifying bacteria (phase I and II) and nitrogenase activity (C2H2 reduction) in an agricultural soil. The presence of 10 to 300 μg/g significantly increased the total number of bacteria and denitrifying bacteria. However, the population of aerobia dinitrogen fixing bacteria and dinitrogen fixation were suppressed significantly. Nitrifying bacteria and fungal populations decreased initially at concentrations of 100 to 300 μg/g but recovered rapidly to levels similar than those in the control.

Liberation of amino acids by heterotrophic nitrogen fixing bacteria

Summary.Large amounts of amino acids are produced by nitrogen-fixing bacteria such as Azotobacter, Azospirillum, Rhizobium, Mesorhizobium and Sinorhizobium when growing in culture media amended with different carbon and nitrogen sources. This kind of bacteria live in close association with plant roots enhanced plant growth mainly as a result of their ability to fix nitrogen, improving shoot and root development suppression of pathogenic bacteria and fungi, and increase of available P concentration. Also, it has been strongly evidenced that production of biologically substances such as amino acids by these rhizobacteria are involved in many of the processes that explain plant-grown promotion. This paper reviews literature concerning amino acids production by nitrogen-fixing bacteria. The role of amino acids in microbial interactions in the rhizosphere and establishment of plant bacterial association is also discussed.

Effect of the insecticides methylpyrimifos and chlorpyrifos on soil microflora in an agricultural loam

A study of the effects of two selected organophosphorus insecticides methylpyrimifos and chlorpyrifos on soil microflora in an agricultural loam was made. The insecticides had concentrations of 10 to 300 μg g−1. The presence of methylpyrimifos at concentrations of 100 to 300 μg g−1 or chlorpyrifos at concentrations from 10 to 300 μg g−1 significantly decreased aerobic dinitrogen fixing bacteria and dinitrogen fixation. Nitrifying bacteria decreased at concentrations of 200 and 300 μg g−1 of methylpyrimifos. The presence of 10 to 300 μg g−1 of chlorpyrifos decreased the total number of bacteria. However, fungal populations and denitrifying bacteria were not affected as a consequence of the addition of the organophosphorus insecticides to the agricultural soil, showing that these microorganisms can tolerate high amounts of those insecticides.

Amino acids and vitamins produced by azotobacter vinelandii atcc 12837 in chemically-defined media and dialysed soil media

Abstract The liberation of amino acids and vitamins by Azotobacter vinelandii ATCC 12837 was studied in chemically-defined media and dialysed soil media. Azotobacter cultured in dialysed soil medium without glucose, showed a very small capacity for amino acid and vitamin synthesis. The production of amino acids and vitamins was increased when Azotobacter was cultured in chemically-defined media, specially when NH4NO3 was added. Arginine was liberated by Azotobacter only in N-free medium. Tryptophane and methionine were produced only when NH4NO3 was added to the N-free medium.

Production of polyhydroxyalkanoates by Azotobacter chroococcum H23 in wastewater from olive oil mills (alpechin)

We describe the production of large amounts of homo- and copolymers of polyhydroxyalkanoates (PHAs) by Azotobacter chroococcum strain H23 when growing in culture media amended with alpechin. A. chroococcum grown on NH4+-medium supplemented with alpechin formed PHAs up to 50% of the cell dry weight after 24h. The results show that alpechin supports the growth of strain H23 and also that this waste could be utilized as a carbon source. Production of PHAs by using alpechin looks promising, since the use of inexpensive feed-stocks for PHAs is essential if bioplastics are to become competitive products. 0 1997 Published by Elsevier Science Limited. All rights reserved

Response of Faba bean (Vicia faba L.) to combined inoculation with Azotobacter and Rhizobium leguminosarum bv. viceae

Mixed inoculation of the grain legume faba bean (Vicia faba L.) with Rhizobium leguminosarum bv. viceae strain Z25 and five different Azotobacter chroococcum or A. vinelandii strains, under gnotobiotic conditions of culture, resulted in significant effects on nodulation, plant growth and nitrogenase activity (acetylene-reduction activity, ARA) of nodulated roots at the flowering stage. A. chroococcum strain H23 and A. vinelandii strains ATCC 12837 and Dv42 promoted plant growth, significantly increasing dry matter accumulation in all plant parts including nodules, as well as total N content. A. chroococcum strain DR26 increased ARA of nodulated roots over 100% when compared with control plants inoculated with Rhizobium alone. Only A. chroococcum strain DR25 decreased plant growth. The effects of each Azotobacter strain are significantly related to viable cell numbers applied as inocula. # 1999 Elsevier Science B.V. All rights reserved.

Effects of the herbicide alachlor on soil microbial activities

A study was made of the effects of one selected acetanilide herbicide, alachlor, at concentrations of 2.0–10.0 kg ha−1 on bacterial populations, fungi, dinitrogen fixation bacteria, denitrifying bacteria, nitrifying bacteria, nitrogenase activity, acid and alkaline phosphatases, arylsulfatase and deshydrogenase. The presence of 2.0–10.0 kg ha−1 of alachlor in the soil increased the total number of bacteria and fungi. The population of denitrifying bacteria increased significantly at concentrations of 5.0–10.0 kg ha−1. However, aerobic dinitrogen fixing bacteria and nitrogenase activity decreased at alachlor concentrations of 3.5–10.0 kg ha−1. Acid and alkaline phosphatases, arylsulfatase and dehydrogenase activity decreased significantly initially at concentrations of 5.0–10.0 kg ha−1, but recovered to levels similar to those in the control. Nitrifying bacteria were not affected as a consequence of the addition of the herbicide to agricultural soil.