Nitrogen-15: microbiological alteration of abundance.

The abundance of N(15) relative to N(14) is significantly altered during experiments in vitro in which nitrate and nitrite are microbiologically reduced to nitrogen gas. In all studies to date, N(14)O(3)-and N(14)O(2)-species have been preferentially reduced. This selectivity has a complex dependence on conditions in the medium. The results are not only relevant to natural variations in N(15) relative to N(14) but should be seriously considered during N(15) tracer studies in soils.

Quantitative assessment of the bacterial rhizosphere flora of Pinus contorta var. latifolia.

The bacterial flora associated with root systems of young and mature lodgepole pine was investigated by sampling forest-grown trees. Counts were performed and expressed on a surface-area basis to give a more realistic comparison of organism density or activity within the control soil, rhizosphere soil, and rhizoplane. On this basis, densities increased by an order of 10(4)- to 10(6)-fold from control soil to rhizoplane, with the degree of stimulation being inversely related to root radius.

Bouyant density, conversion formulae, and the mole percent guanosine + cytosine content of Desulfovibrio sp.

A reevaluation of the original buoyant density conversion formula used to calculate the molar percentage guanosine + cytosine (% G + C) contents of the accepted species of genus Desulfovibrio has been undertaken. It would appear that the formula used gives values 4-5% lower than those obtained using formulae more generally cited in modern literature. Recalculations of % G + C content values for Lesulfovibrio DNA are presented using the formulae of three different workers, and are compared with those values originally used in the classification of genus Desulfovibrio.

Microbial utilization of crude oil.

The utilization of two crude oil samples of different quality at 4 and 30 C has been studied by using pure and mixed bacterial cultures obtained by enrichment procedures. Growth, emulsification, and utilization occurred readily at both temperatures. The crude oil residue is increased in specific gravity and readily sediments out of solution. A comparison of the chemical analysis of the oils by liquid and gas-liquid chromatographic procedures before and after growth showed that the n-saturate fraction had been preferentially used. Some utilization of the aromatic fraction also occurred. Enrichments obtained with a high-quality crude oil were not as effective in utilizing a lower quality crude oil as sole carbon source as a population enriched on the low-quality crude oil.

Effect of nitrate on reduction of ferric iron by a bacterium isolated from crude oil.

A Pseudomonas sp. isolated from crude oil reduced ferric ions (Fe(III)) to ferrous ions (Fe(II)). In the presence of nitrate (NO3-) after prolonged incubation, the amount of Fe(II) was lower than in its absence. However, during short incubation periods, the presence of NO3- significantly increased (99.5% confidence limit) the amount of Fe(II) produced. The decrease in Fe(II) on prolonged incubation was associated with increased production and accumulation of nitrite (NO2-). Under low NO3- levels, where the production of NO2- was limited, a decrease in NO2- concentration was accompanied by an increase in Fe(II) production to levels comparable with those obtained in the absence of NO3-. Preinduction of cells for nitrate reductase, which favoured rapid NO2- production, resulted in a more rapid decrease in Fe(II) production than in cells that were not preinduced. It is proposed that the inhibitory effect of NO3- on microbial reduction of Fe(III) is due to a secondary reaction, which involves the chemical oxidation of Fe(II) by NO2-.

In situ degradation of oil in a soil of the boreal region of the Northwest Territories.

Replicate field plots comprising a control; control plus oil; control plus oil and fertilizer (urea phosphate, 27:27:0); control plus oil and bacteria; and control plus oil, fertilizer, and bacteria were established at Norman Wells, N.W.T., Canada. Plots were monitored over a 3-year period for changes in microbial numbers and the chemical composition of recovered oil. Where fertilizer was applied, there was a rapid increase in bacterial numbers, but no increase in fungal propagules. This was followed by a rapid disappearance of n-alkanes, isoprenoids, and a continuous loss in weight of saturate compounds in recovered oil. Changes in the content of asphaltenes, aromatics, and nitrogen-, sulphur-, and oxygen-containing fractions also are discussed. The seeding of oil-soaked plots with oil-degrading bacteria did not have any effect on the composition of recovered oil. Fertilized plots showed a more rapid rate of vegetation with cotton grass and Labrador tea being the dominant species in revegetation.

Characterization of the bacterial flora associated with root systems of Pinus contorta var. latifolia.

Root systems of young and mature lodgepole pine (Pinus contorta Dougl. var. latifolia Englem.) were removed from forest stands and the associated aerobic bacterial flora isolated. Characterization of rhizoplane and control soil isolates from these tree root systems demonstrated differences from that reported for agricultural crops. Ammonifying, proteolytic, and amylolytic organisms were proportionately reduced within the rhizoplane. The rhizoplane organisms grew more slowly than the control soil isolates, although they responded in greater numbers to the addition of an amino acid supplement to the growth media. The rhizoplane organisms also showed an increased ability to solubilize phosphate. The chitinolytic organisms were suppressed within the rhizoplane of the mature tree but were stimulated by the young trees. With this exception, the rhizoplane microflora of older and younger trees were similar.

Microbial utilization of raw and hydrogenated shale oils.

The biodegradability of raw and hydrogenated shale oils prepared by a retort process were studied under psychrophilic and mesophilic conditions. Changes in bacterial numbers and the chemical composition of the oils were monitored using a plate count and chromatographic techniques respectively. Raw shale oil was found to be relatively resistant to microbial attack whereas hydrogenated shale oil was readily utilized for microbial growth. Populations enriched on raw shale oil had a reduced ability to use hydrogenated shale oil under similar conditions. Gram-negative rods predominated in all enrichment populations. It is recommended that to facilitate clean up of shale oil spills, raw shale oil be reduced at the extraction site before transport.

Effect of amendments on the microbial utilization of oil applied to soil.

Replicate field plots comprising a control, plus oil, plus oil and bacteria, plus oil and fertilizer (urea-phosphate; 27:27:0), and plus oil, bacteria, and fertilizer were monitored over a 308-day period for changes in bacterial and mold numbers. Changes in the chemical composition of the oil applied to the plots was followed by using chromatographic techniques. Application of fertilizer resulted in a stimulation of bacterial numbers and in the rate of utilization of n-alkane components of the saturate fraction. The application of oil-utilizing bacteria, however, resulted in only a slightly accelerated rate of utilization of n-alkane components of chain lengths C20 to C25. The isoprenoids, phytane and pristane, were still present in gas-liquid chromatography profiles after digestion of the n-alkane components of the saturate fraction. Those plots which received fertilizer showed an accelerated rate of recovery of native vegetation.

Urbanization and the microbial content of the north Saskatchewan River.

The effect of urbanization on the microbial content of the North Saskatchewan River was determined by following the changes in the numbers of total bacteria, total eosin methylene blue (EMB) plate count, and Escherichia coli as the river flowed from its glacial source, through parklands, and out into the prairies. Changes in physical parameters such as pH, temperature, salt concentration, and the amount and nature of the suspended material were also determined to evaluate their on the microbial parameters being measured. The level of all three microbial parameters studied slowly increased as the river flowed from its glacial source out into the prairies. The major effect of small hamlets, with or without sewage treatment facilities, appears to be to supply nutrients which supports the growth of the indigenous river flora but not E. coli. In contrast, the effect of a large urban center, with a population of approximately 500,000, which utilizes primary and secondary sewage processes in disposing of sewage, is to provide the nutrients and an inoculum of E. coli which results in a marked increase in the numbers of all three microbial groups studied. The effect of this urban center was still discernible 300 miles downstream. The river was also monitored for the presence of Salmonella sp. Only one positive isolation was achieved during this study, and this isolate was characterized as being Salmonella alachua.

Surface changes in mild steel coupons from the action of corrosion-causing bacteria.

Changes which occur on the surface of mild steel coupons submerged in cultures of an Fe(III)-reducing bacterium, isolated from corroded pipe systems carrying crude oil, were studied microscopically to investigate the interaction between the corrosion-causing bacterium and the corroding mild steel coupon. Under micro-aerobic conditions and in the absence of the bacteria, a dense, crystalline, amorphous coat formed on the surface of the steel coupons. In the presence of bacteria the surface coat was extensively removed, exposing the bare metal to the environment. After about 2 weeks of exposure, the removal of the surface coating was followed by colonization of the metal surface by the bacteria. Colonization was mediated by fibrous, exopolysaccharidic material formed by the bacteria. Extension of studies to other bacteria isolated from crude oil and corroded pipes reveals that the formation of exopolysaccharide fibers and possession of adherent properties are common characteristics of bacteria from crude oil systems.