Nontuberculous mycobacteria in soils of La Pampa province (Argentina).

The presence of nontuberculous mycobacteria (NTM) was investigated in forty soil samples belonging to the four physiographic regions (Eastern, Central, Southern and Western) that constitute La Pampa province. The presence of NTM in 67.5% of these soil samples was determined. The density of mycobacteria ranged 25-4,500 mycobacteria g-1 dry soil (mean = 516 CFU g-1). Significant differences were found in relation to both the investigated regions (p < 0.01) and the soil pH (r = 0.44*) (P = 0.02). The mycobacteria represented less than 0.00001% of the total aerobic bacteria found in the soils. Twenty-seven isolated mycobacteria were classified according to the culture, biochemical, enzymatic characteristics and antibiotic sensitivity. Mycobacterium fortitium was the dominant mycobacterium and was detected in 63% of the positive soils. This species showed ability for living in sandy to sandy loam soils, within a wide pH range (6.5-9.7) and organic matter (4.15-83.63 g kg-1). Two other species were M. phlei (range = 50-4,500 CFU g-1) and M. kansasii (range = 50-500 CFU g-1).

Nontuberculous mycobacteria in soils of La Pampa province (Argentina)

The presence of nontuberculous mycobacteria (NTM) was investigated in forty soil samples belonging to the four physiographic regions (Eastern, Central, Southern and Western) that constitute La Pampa province. The presence of NTM in 67.5 of these soil samples was determined. The density of mycobacteria ranged 25-4,500 mycobacteria g-1 dry soil (mean = 516 CFU g-1). Significant differences were found in relation to both the investigated regions (p < 0.01) and the soil pH (r = 0.44*) (P = 0.02). The mycobacteria represented less than 0.00001 of the total aerobic bacteria found in the soils. Twenty-seven isolated mycobacteria were classified according to the culture, biochemical, enzymatic characteristics and antibiotic sensitivity. Mycobacterium fortitium was the dominant mycobacterium and was detected in 63 of the positive soils. This species showed ability for living in sandy to sandy loam soils, within a wide pH range (6.5-9.7) and organic matter (4.15-83.63 g kg-1). Two other species were M. phlei (range = 50-4,500 CFU g-1) and M. kansasii (range = 50-500 CFU g-1).(AU)

Nontuberculous mycobacteria in soils of La Pampa province (Argentina)

The presence of nontuberculous mycobacteria (NTM) was investigated in forty soil samples belonging to the four physiographic regions (Eastern, Central, Southern and Western) that constitute La Pampa province. The presence of NTM in 67.5 of these soil samples was determined. The density of mycobacteria ranged 25-4,500 mycobacteria g-1 dry soil (mean = 516 CFU g-1). Significant differences were found in relation to both the investigated regions (p < 0.01) and the soil pH (r = 0.44*) (P = 0.02). The mycobacteria represented less than 0.00001 of the total aerobic bacteria found in the soils. Twenty-seven isolated mycobacteria were classified according to the culture, biochemical, enzymatic characteristics and antibiotic sensitivity. Mycobacterium fortitium was the dominant mycobacterium and was detected in 63 of the positive soils. This species showed ability for living in sandy to sandy loam soils, within a wide pH range (6.5-9.7) and organic matter (4.15-83.63 g kg-1). Two other species were M. phlei (range = 50-4,500 CFU g-1) and M. kansasii (range = 50-500 CFU g-1).

Nontuberculous mycobacteria in soils of La Pampa province (Argentina).

The presence of nontuberculous mycobacteria (NTM) was investigated in forty soil samples belonging to the four physiographic regions (Eastern, Central, Southern and Western) that constitute La Pampa province. The presence of NTM in 67.5

of these soil samples was determined. The density of mycobacteria ranged 25-4,500 mycobacteria g-1 dry soil (mean = 516 CFU g-1). Significant differences were found in relation to both the investigated regions (p < 0.01) and the soil pH (r = 0.44*) (P = 0.02). The mycobacteria represented less than 0.00001

of the total aerobic bacteria found in the soils. Twenty-seven isolated mycobacteria were classified according to the culture, biochemical, enzymatic characteristics and antibiotic sensitivity. Mycobacterium fortitium was the dominant mycobacterium and was detected in 63

of the positive soils. This species showed ability for living in sandy to sandy loam soils, within a wide pH range (6.5-9.7) and organic matter (4.15-83.63 g kg-1). Two other species were M. phlei (range = 50-4,500 CFU g-1) and M. kansasii (range = 50-500 CFU g-1).

Spatio-temporal distribution of naturally occurring Bacillus spp. and other bacteria on the phylloplane of soybean under field conditions.

Bacterial populations were surveyed on phylloplane of field-grown soybean every 20 days in southern Buenos Aires, Argentina. The crop was disease-free and no pesticides were applied. Out of 523 bacterial isolates (mainly Gram positive bacteria) from upper and lower leaves, 134 of them were Bacillus spp. Bacillus pumilus was the dominant species followed by Bacillus subtilis. The proportion of Bacillus spp. decreased from 80% of all bacterial isolates in early stages to 0% at harvest, whereas the diversity of Bacillus spp. decreased from nine species at day 45, to one species at day 133, shortly before harvest. Among the isolates, a significant increase in the percentage of nitrifiers with plant aging was observed on lower and upper trifoliates. In contrast, proteolytic bacteria were more abundant on lower than on upper trifoliates at all sampling dates. The consistent recovery of B. pumilus from soybean phylloplane during most of the crop cycle indicated this species as an interesting candidate for future plant microbial management and biocontrol studies.

Influence of pH on the toxicity and survival of total cells and spores of Bacillus thuringiensis.

B. thuringiensis (Bt) is one of the most important microorganism among those studied because of their entomopathogenic potential against insect plagues and vectors. In this work, the pathogenicity and survival of total cells and spores of three autochthonous strains of B. thuringiensis isolated from Argentine soils (A61, A27 and A68) and the commercial strain HD-1 were studied at different ion hidrogen concentrations (pH = 4.4; 5.4; 7.4; 8.4; 9.4 and 10.4) under laboratory conditions. The greatest antimicrobial effect on the number of spores and total cells was observed at pH 4.4 with a great decrease after 72 hours' growth. Comparing the survival percentage of total cells and spores; pH 5.4 was the one which allowed the higher relative tolerance (survival) among the studied strains. No decrease in pathogenicity was observed in the investigated serotypes at different pHs in bioassays against Cydia pomonella. Two soil strains of Bt (A61/A27) and the Bt (HD-1) of commercial origin caused the highest mortality of the target insect. The sotto serotype (A68), however, did not produce this effect.

Influence of pH on the toxicity and survival of total cells and spores of Bacillus thuringiensis

Entre los grupos de microorganismos que se estudian por su potencial entomopatógeno, B. thuringiensis (Bt) es sin lugar a dudas la bacteria de mayor importancia en el control de insectos, plagas y vectores. En este trabajo se estudió la patogenicidad y sobrevivencia de células totales y de esporas de tres cepas de B. thuringiensis autóctonas de suelos argentinos (A61, A27 y A68) y una cepa comercial HD-1, a distintas concentraciones de ión hidrógeno (pH=4,4; 5,4;7,4; 8,4; 9,4 y 10,4), bajo condiciones de laboratorio. No se observó disminución de la toxicidad de las cepas desarrolladas a distintos valores de pH en bioensayos contra Cydia pomonella. El mayor efecto antimicrobiano sobre el número de esporas y células totales se detectó a pH 4,4. El pH 5,4 fue el que permitió un mayor índice de sobrevivencia en los serotipos investigados. Tres cepas de Bt (A61,A27,HD-1) mostraron alta toxicidad contra C. pomonella. El serotipo sotto, sin embargo, no produjo ese efecto (AU)

Influence of pH on the toxicity and survival of total cells and spores of Bacillus thuringiensis

Entre los grupos de microorganismos que se estudian por su potencial entomopatógeno, B. thuringiensis (Bt) es sin lugar a dudas la bacteria de mayor importancia en el control de insectos, plagas y vectores. En este trabajo se estudió la patogenicidad y sobrevivencia de células totales y de esporas de tres cepas de B. thuringiensis autóctonas de suelos argentinos (A61, A27 y A68) y una cepa comercial HD-1, a distintas concentraciones de ión hidrógeno (pH=4,4; 5,4;7,4; 8,4; 9,4 y 10,4), bajo condiciones de laboratorio. No se observó disminución de la toxicidad de las cepas desarrolladas a distintos valores de pH en bioensayos contra Cydia pomonella. El mayor efecto antimicrobiano sobre el número de esporas y células totales se detectó a pH 4,4. El pH 5,4 fue el que permitió un mayor índice de sobrevivencia en los serotipos investigados. Tres cepas de Bt (A61,A27,HD-1) mostraron alta toxicidad contra C. pomonella. El serotipo sotto, sin embargo, no produjo ese efecto

[Dynamics of bacteria from the phyllosphere and leaves of soy (Glycine max L. Merrill) in field conditions]. / Dinámica de las bacterias de la filosfera y hojarasca de soja (Glycine max L. Merrill) en condiciones de campo.

The surfaces of aerial plant provide a habitat for epiphitic microorganisms many of which are capable of influencing the growth of pathogens. In this study, fluctuation of bacterial population occurring in different growth stages of soybean leaves (Glycine max L Merrill) was examined using the dilution plate method. Three culture media were applied; invariably, the numbers of bacteria increased with increasing plant age. The total number of bacteria living on the detached leaves were ten times higher than leaves surfaces of soybean Asgrow 3127 (Group III). One hundred and seventy-five heterotrophic bacteria were obtained from both the phyllosphere and litter of the plant. Of these, fifty-one microorganisms (29%) were classified as members of the genus Bacillus; the remainder were mainly members of the irregular, nonsporing, Gram positive rods (coryneform bacteria). Approximately 52% of the total coryneform bacteria isolated was found to belong to the following two clusters: Arthrobacter and Corynebacterium. There were few Pseudomonas strains and 75% of the total isolated bacteria were able to grow in N-poor culture medium.