RESUMEN
The method of membrane filters was used to study the population dynamics of bacteria belonging to the genera Arthrobacter, Flavobacterium, and Klebsiella in barley (Hordeum vulgare) rhizosphere under conditions of cadmium stress (5-15 mg Cd/g soil). Mathematical modeling allowed us to demonstrate that the phytoprotective effect is implemented via the following succession of events: the bacteria synthesize phytohormones (IAA and ethylene)-->root excretory activity increases-->the number of the bacteria in the rhizoplane grows-->the flux of bacteria migrating from the rhizoplane to the rhizosphere increases-->the number of bacteria binding cadmium ions in the rhizosphere grows-->the amount of free ions entering the plant decreases. Among the bacteria studied, K. mobilis 880 displayed the highest migration and immobilization activity and the best survival rate under conditions of cadmium stress. Consequently, K. mobilis 880 is recommended for use in biopreparations for stimulating plant growth under conditions of heavy metal pollution.
Asunto(s)
Cadmio , Flavobacterium/fisiología , Hordeum/microbiología , Hordeum/fisiología , Modelos Teóricos , Microbiología del Suelo , Agricultura/métodos , Arthrobacter/aislamiento & purificación , Arthrobacter/fisiología , Cadmio/metabolismo , Recuento de Colonia Microbiana , Flavobacterium/aislamiento & purificación , Klebsiella/aislamiento & purificación , Klebsiella/fisiología , Reguladores del Crecimiento de las Plantas/metabolismo , Raíces de Plantas/microbiología , Raíces de Plantas/fisiología , Contaminantes del Suelo/metabolismo , SimbiosisRESUMEN
Some metabolic peculiarities of bacteria of the genus Klebsiella were investigated. The bacteria under study were isolated from different sources and varied in virulence. The pathogenic and saprotrophic enterobacteria were discriminated based on their response to the addition of carbohydrates or nitrate to the medium. Pathogenic Klebsiella spp. exhibited mainly the mixed formic-acid type of fermentation and were more resistant to nitrates than saprotrophic bacteria with the butanediol type of fermentation. The bacteria Klebsiella pneumoniae subsp. pneumoniae isolated from different sources, such as patients, healthy persons, or the environment, exhibited no substantial differences in metabolism and virulence. It was inferred that these bacteria themselves cannot cause disease, and their isolation in morbid states is an indirect result of dysbacteriosis.
Asunto(s)
Klebsiella/metabolismo , Metabolismo de los Hidratos de Carbono , Fermentación , Klebsiella/patogenicidad , Nitratos/metabolismo , Especificidad de la Especie , VirulenciaRESUMEN
The effect of carcinogenic N-nitrosoamines (NA), NA-producing tetramethylthiuram disulfide (TMTD) pesticide, and of various doses of nitrogen fertilizers (90, 180, and 270 kg/ha) on the forming and vital functions of microbiocenosis of light gray forest soil was studied. The quantity, nitrifying activity, and gas production of nitrifying bacteria increased under the influence of NA. The nitrosodimethylamine (NDMA) and the nitrosodibutilamine (NDBA) changed the correlation between the number of soil-inhabiting fungi and bacteria so that the former prevailed. The greatest effect was observed on the twentieth day of cultivation of the soil when high concentrations of NDMA (50 mcg/kg) and NDBA (105 mcg/kg) were used. The typical dominant species among the fungi was the phytotoxigenic Penicillium funiculosum. The nitrosationable pesticide tetramethylthiuram disulfide (TMTD) applied with nitrogen fertilizers in a dose of 180 and 270 kg/ha exerted an influence on the microbiocenosis of the soil similar to NA. The potato yield decreased and the ecology of microbiocenosis deteriorated under these conditions in a model vegetable experiment. It is suggested that the nitrosoamines and their precursors may change the balance of nitrogen, decrease the yield of plants, and deteriorate the ecological balance.
Asunto(s)
Nitrosaminas/farmacología , Microbiología del Suelo , Solanum tuberosum/efectos de los fármacos , Tiram/farmacología , Dimetilnitrosamina/farmacología , Modelos Biológicos , Solanum tuberosum/crecimiento & desarrollo , Factores de TiempoRESUMEN
While comparatively analyzing the properties of Klebsiella pneumoniae from three studied sources (patients, healthy people, environment), no reliable differences between the comparable strains have been revealed. No differences have been found in the toxin formation, hemagglutinating and antilysozymic activity, adhesivity and invasive properties as well as in the peculiarities of gas exchange, while growing on media with different nitrogen and carbon sources. The studied microorganisms differed only in antibiotic resistance: strains isolated from the environment were sensitive to antibiotics, whereas strains of human origin were resistant to them.