Biomedical subjects

G W Marengo

Publications and source records attributed to G W Marengo.

3 recordsLinked to original sources

PubMed1984

[Nitrification in soil columns subjected to continuous flow].

Nitrification in columns of soil under continuous flow of substrate was studied. The soil was previously diluted with sterile sand (1 part of soil: 9 parts of sand; w : w) and admixed with 2% CaCO3. Soil columns, 15 cm high, were contained in glass cylinders with a cross sectional area of 39.6 cm2. In the main experiment, a soil column was subjected to the continuous flow of a KNO2 solution (100 ppm NO2- - N) at a flow rate of 46.0 cm3 h-1. An exponential increase of nitrate concentration in the column effluent was observed during the first 4 days (Fig. 1), suggesting an exponential growth of NO2- oxidizers in the soil column, with an apparent generation time of 1, 2 days. At the end of this phase, an almost complete conversion of nitrite to nitrate was reached followed by an important decrease in conversion and by a partial recovery with stabilization at 69 ppm NO3- - N in the column effluent. This phenomenon was presumably due to a rapid rate of O2 demand by the microorganisms which exceeded the supply, and to the subsequent adaptation of the NO2- oxidizers to a situation in which the O2 concentration was the limiting factor. At the end of the experiment, the average population density of NO2- oxidizers in the column was 1.5. 10(7) cells cm-3. In a preliminary experiment, a column of the same soil was continuously perfused with an (NH4)2SO4 solution with 140 ppm NH+4 - N, at a constant rate of 40.8 cm3 h-1 (Fig. 2.).(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗

PubMed1983

[Encystment using different carbon substrates in Azotobacter chroococcum].

Carbon nutrition has a fundamental role in the encystment of bacteria of the genus Azotobacter. The effect of liquid media with various organic carbon substrates on the encystment of 2 strains of Azotobacter chroococcum was studied. Both strains had been previously cultured in a glucose and mannitol liquid medium. Strain 2087 showed the greatest degree of encystment (78%) with isopropanol and a very low percentage of cyst formation in the glucose and mannitol medium. In strain 1847 an important percentage of cyst formation (33%) was obtained in the glucose and mannitol medium and no cysts appeared with isopropanol. N-butanol and N-propanol induced in both strains relatively reduced percentages of encystment. The differential response found in the glucose and mannitol medium and the isopropanol media with strains 2087 and 1847 of A. chroococcum, has a degree of similarity in the different intensity of encystment shown by diverse strains of A. vinelandii with certain carbon substrates.

Azotobacter↗

PubMedDate not supplied

[Complete nitrification in soil columns perfused with nitrite].

Four columns of the same soil were put under the continuous flow of a NaNO2 solution [50 ppm N], so as to follow the evolution of nitrification. The soil, the columns as well as the solution continuous flow regulating system, were prepared as in the previous experiments. The columns, with the exception of No1 (control), contained also the following substances: No2 and 4: 2% de CaCO3 and No3 and 4:0.0015% SO - 4-S. Since the eight day of perfusion all the effluents had an important concentration of nitrate (Figure 1), exceeding in them, the sum of [No-2-N] an [NO-3-N] (Table 1) the concentration of th NO-2-N of the perfusion solution. Finally, the [NO-2-N] was reduced importantly in the effluents, and the (NO-3N), in all of them, stabilized itself as values nearing 50 ppm. Its suggested that at the beginning of the experiment, an endogenous source of NO-2 was functioning, which could explain the observed phenomenon, and that later it ceased to do so. The populational density of NO-2 oxidizers increased, during the experiment, 49 times (Table 2). An increase was also measured in the populational density of NH+4 oxidizers, which amounted to 41 times. This later fact contributes to support the existence of an endogenous provision of NO-2 during the initial part of the experiment.

Bacteria↗