C. Pozo

Effects of culture conditions on the production of polyhydroxyalkanoates by Azotobacter chroococcum H23 in media containing a high concentration of alpechín (wastewater from olive oil mills) as primary carbon source.

Large amounts of homopolymers containing beta-hydroxybutyrate (PHB) and copolymers containing beta-hydroxyvalerate (P[HB-co-HV]) are produced by Azotobacter chroococcum strain H23 when growing in culture media amended with alpechín (wastewater from olive oil mills) as the sole carbon source. Copolymer was formed when valerate (pentanoate) was added as a precursor to the alpechín medium, but it was not formed with the addition of propionate as a precursor. A. chroococcum formed homo- and copolymers of polyhydroxyalkanoates (PHAs) up to 80% of the cell dry weight, when grown on NH(4)(+)-medium supplemented with 60% (v/v) alpechín, after 48 h of incubation at 100 rev min(-1) and 30 degrees C. Production of PHAs by strain H23 using alpechín looks promising, as the use of a cheap substrate for the production of these materials is essential if bioplastics are to become competitive products.

Production of B-group vitamins by two Azotobacter strains with phenolic compounds as sole carbon source under diazotrophic and adiazotrophic conditions

Azotobacter vinelandii strain ATCC 12837 and A. chroococcum strain H23 (CECT 4435) were able to grow on N‐free or NH4Cl‐amended chemically‐defined (Burks) media, with protocatechuic acid (1–2 mmol l−1) or sodium p‐hydroxybenzoate (1–10 mmol l−1) as sole carbon (C) sources. At a concentration of 2 mmol l−1, both substrates supported nitrogen fixation (acetylene reduction assay) at similar or higher rates than bacteria grown in control media amended with 2 mmol l−1 sodium succinate as C source. The two strains produced the B‐group vitamins niacin, pantothenic acid, thiamine, riboflavin and biotin after 72 h of growth in chemically‐defined media with 2 mmol l−1 protocatechuic acid, sodium p‐hydroxybenzoate or sodium succinate as sole C source, either in N‐free media or in media amended with 0·1% NH4Cl. Quantitative production of all vitamins was affected by the use of the different C and N substrates.

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.

Microbial enzymatic activities in a pilot-scale MBR experimental plant under different working conditions.

Phosphatases, glucosidase, protease, esterase and dehydrogenase activities in a MBR (membrane bioreactor) system equipped with ultrafiltration membranes for the treatment of real urban wastewater were measured at different volatile suspended solid (VSS) concentrations, total suspended solid (TSS) concentrations, hydraulic retention times (HRT), temperatures and inflow rates. The results showed the capacity of the MBR system to remove COD and BOD(5) at TSS between 7200 and 13,300 mg/L; HRT values of 8.05 and 15.27 h; inflow rates of 14.67 and 27.81 L/h; and temperatures between 4 and 27 degrees C. The enzymatic activities are influenced by increases in VSS and TSS concentrations. These results suggest that the ability to get adapted to environmental changes of the bacterial populations and their microbial enzymatic activities is essential to understand the biological processes that occur in MBR systems and crucial for proper urban wastewater treatment when using MBR technologies.

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.

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.

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

Production of B‐group vitamins by two Rhizobium strains in chemically defined media

Twenty‐eight strains of Rhizobium spp. were tested for their ability to grow in chemically‐defined medium lacking growth factors. Two strains, R. meliloti GR4B and Rhizobium spp. (Acacia) GRH28, were selected, on the basis of their good growth under the conditions imposed, for further quantification of the production of water‐soluble vitamins (thiamine, niacin, riboflavin, pantothenic acid and biotin) in chemically defined media amended with different compounds (mannitol, glucose or sodium succinate) as sole carbon sources. Qualitative and quantitative production of vitamins in chemically‐defined media was significantly affected by the use of C sources of a different nature and the age of the cultures. Strain GRH28 produced all the vitamins analysed, and high biological levels of biotin (14 ng ml–1 culture) were detected after 6 d of culture in mineral medium amended with mannitol. Pantothenic acid was the vitamin detected in the highest amounts (up to 1 μg ml–1 of culture) in culture supernatant fluids of strain GR4B grown for 6 d with succinate as sole carbon source.

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.

Selection and identification of bacterial strains with methyl-tert-butyl ether, ethyl-tert-butyl ether, and tert-amyl methyl ether degrading capacities.

Nine bacterial strains isolated from two hydrocarbon-contaminated soils were selected because of their capacity for growth in culture media amended with 200 mg/L of one of the following gasoline oxygenates: Methyl-tert-butyl ether (MTBE), ethyl-tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). These strains were identified by amplification of their 16S rRNA gene, using fDl and rD1 primers, and were tested for their capacity to grow and biotransform these oxygenates in both mineral and cometabolic media. The isolates were classified as Bacillus simplex, Bacillus drentensis, Arthrobacter sp., Acinetobacter calcoaceticus, Acinetobacter sp., Gordonia amicalis (two strains), Nocardioides sp., and Rhodococcus ruber. Arthrobacter sp. (strain MG) and A. calcoaceticus (strain M10) consumed 100 (cometabolic medium) and 82 mg/L (mineral medium) of oxygenate TAME in 21 d, respectively, under aerobic conditions. Rhodococcus ruber (strain E10) was observed to use MTBE and ETBE as the sole carbon and energy source, whereas G. amicalis (strain T3) used TAME as the sole carbon and energy source for growth. All the bacterial strains transformed oxygenates better in the presence of an alternative carbon source (ethanol) with the exception of A. calcoaceticus (strain M10). The capacity of the selected strains to remove MTBE, ETBE, and TAME looks promising for application in bioremediation technologies.