Variability in Effectiveness of Rhizobia during Culture and in Nodules

The ability of three strains of Bradyrhizobium sp. (Vigna) to fix dinitrogen in symbiotic association with siratro (Macropitilium atropurpureum) was measured after culture in broth and after isolation from nodules. Seven transfers were made between the initial broth culture and the final broth culture. A total of 40 single-colony isolates were obtained from cultures 1 and 7 to test effectiveness. Variation in dinitrogen-fixing effectiveness of the population of one strain did not change on culturing, whereas there was considerable variation in effectiveness of populations of the other two strains. Generally, single-colony isolates from individual nodules had similar levels of effectiveness, but some exceptions occurred. Isolates from different nodules formed by the same Bradyrhizobium strain often differed in their effectiveness.     

Growth determinations for unattached bacteria in a contaminated aquifer.

Growth rates of unattached bacteria in groundwater contaminated with treated sewage and collected at various distances from the source of contamination were estimated by using frequency of dividing cells and tritiated-thymidine uptake and compared with growth rates obtained with unsupplemented, closed-bottle incubations. Estimates of bacterial generation times [(In 2)/mu] along a 3-km-long transect in oxygen-depleted (0.1 to 0.7 mg of dissolved oxygen liter-1) groundwater ranged from 16 h at 0.26 km downgradient from an on-land, treated-sewage outfall to 139 h at 1.6 km and correlated with bacterial abundance (r2 = 0.88 at P less than 0.001). Partitioning of assimilated thymidine into nucleic acid generally decreased with distance from the contaminant source, and one population in heavily contaminated groundwater assimilated little thymidine during a 20-h incubation. Several assumptions commonly made when frequency of dividing cells and tritiated-thymidine uptake are used were not applicable to the groundwater samples.     

Influence of Physical Disruption on Growth of Attached Bacteria

Attached bacterial populations cultured without an exogenous carbon source or grown in conjunction with attached diatoms incorporated [³H]thymidine at a rate between four and five times lower than that of replicate bacterial populations which were dispersed before being assayed.     

Alternative nonlinear model for estimating second-order rate coefficients for biodegradation.

A modification of the second-order model for biodegradation was derived, applied to an example data set, and shown to be superior for describing the anaerobic biodegradation of p-cresol by an enriched bacterial consortium. The modified model circumvents the no-growth assumption implicit in the use of the second-order rate equation, but still requires the assumption of first-order kinetics over the course of substrate depletion. Violation of the no-growth assumption is particularly important since overestimates of the pseudo-first-order rate coefficient lead to underestimates of the time required for the removal of a xenobiotic chemical from a contaminated environment. Our calculations show that the errors introduced into the pseudo-first-order rate coefficient (and the resulting estimates of the second-order rate coefficient) approach 100% if one doubling occurs in activity over the course of substrate depletion. For an exemplary data set, use of a first-order model resulted in a 100% overestimate of the first-order decay coefficient, which would in turn lead to a corresponding overestimate of the second-order rate coefficient. The modified model we describe is a potential alternative to the pseudo-first-order model for the routine estimation of second-order rate coefficients.     

Effect of Bacteriophage on Colonization of Sugarbeet Roots by Fluorescent Pseudomonas spp

The colonization potential of two fluorescent Pseudomonas strains (M11/4, B2/6) that exhibit antifungal activity in vitro was studied on the roots of sugarbeet plants in a clay loam soil. The cell density of the introduced bacteria declined on the root system over a 16-day test period in nonsterile soil. Strain B2/6 declined at a significantly faster rate compared with M11/4. This loss in viability and difference in colonization ability between M11/4 and B2/6 was not observed in sterile soil. Nutrient deprivation induced by indigenous microorganisms was excluded as a key factor involved in the decline of the introduced bacteria on the basis that strains M11/4 and B2/6 retained viability when subjected to nutrient starvation conditions over a 16-day period. Experiments designed to test whether antagonism by indigenous microorganisms was responsible for the decline in the introduced fluorescent Pseudomonas sp. population revealed the presence of large numbers of bacteriophage in the soil capable of lysing strain B2/6. Reconstitution experiments carried out with sugarbeet seedlings inoculated independently with strains M11/4 and B2/6 and grown in sterile soil to which a soil phage filtrate had been added showed a significant decrease in the viability of strain B2/6 relative to M11/4. Phage antagonistic toward strain B2/6 were detected in 43% of soils taken from the major sugarbeet growing regions of Ireland.     

Attachment as a factor in the protection of Enterobacter cloacae from chlorination.

Enterobacter cloacae attached to drinking water distribution particles was subjected to chlorination. Attachment resulted in the protection of these organisms from disinfection. This effect was found to be dependent upon both the level of chlorine in the system and attachment time. The results obtained in this study indicate that attached organisms may play an important role in coliform outbreaks.     

An A-ELISA to detect hepatitis A virus in estuarine samples.

An amplified enzyme-linked immunosorbent assay (A-ELISA) for detecting and quantifying hepatitis A virus in estuarine water samples is described. The test was five times more sensitive than a standard ELISA and at least two times more sensitive than radioimmunoassay. Test sensitivity was unaffected by the procedures used to concentrate the virus in estuarine samples or by the presence of humic and tannic acids in test samples. Nonspecific reactions were not encountered with a number of enteroviruses or with a rotavirus. A high sensitivity and specificity combined with speed, low cost, and freedom from radiolabels made the A-ELISA useful for detecting hepatitis A virus in environmental samples. The virus was detected in 3 of 20 estuarine water samples examined by A-ELISA.     

Growth and fermentation of an anaerobic rumen fungus on various carbon sources and effect of temperature on development.

An anaerobic fungus (strain R1) resembling Neocallimastix spp. was isolated from sheep rumen. When grown on defined medium, the isolate utilized a wide range of polysaccharides and disaccharides, but of the eight monosaccharides tested only fructose, glucose, and xylose supported growth. The organism had doubling times of 5.56 h on glucose and 6.67 h on xylose, and in each case fermentation resulted in production of formate, acetate, lactate, and ethanol. During active growth, formate was a reliable indicator of fungal biomass. Growth on a medium containing glucose and xylose resulted in a doubling time of 8.70 h, but diauxic growth did not occur since both sugars were utilized simultaneously. The optimum temperature for zoospore and immature plant development was 39 degrees C, and no development occurred below 33 degrees C or above 41 degrees C.     

Cytotoxic and cytolytic activity of nonadecafluoro-n-decanoic acid on Acholeplasma laidlawii.

We studied the interactions between the perfluorinated fatty acid nonadecafluoro-n-decanoic acid (NDFDA) and the cell wall-less procaryote Acholeplasma laidlawii, which were cultured in an identical medium base but with different serum supplements. When grown in mycoplasma media supplemented with PPLO serum fraction (Difco Laboratories, Detroit, Mich.), A. laidlawii was rapidly killed by low concentrations of toxicant (less than 1.0 mM). At higher concentrations (greater than 10 mM), NDFDA treatment appeared to lyse cells. A. laidlawii cells grown in horse serum-supplemented mycoplasma media were both killed and lysed at the same NDFDA concentration (greater than 10 mM). These data suggest that this perfluorinated fatty acid can be cytotoxic and cytolytic to mycoplasmas. Changes in active concentrations occurred in parallel with changes in growth medium serum supplementation, which is known to alter mycoplasma membrane composition. We propose that NDFDA interacts with the membranes of A. laidlawii cells, resulting in cell death or cell lysis or both.     

Improved membrane filtration media for enumeration of total coliforms and Escherichia coli from sewage and surface waters.

Two media were developed that allowed both a total coliform count and an Escherichia coli count to be determined on the same medium after 24 h of incubation at 35 degrees C. The new media were tested along with two standard media on 10 surface water and 7 sewage samples. The experimental media yielded equivalent or higher counts relative to the standard media and recovered more specifically the desired indicator groups as determined by colony identification.