Biomedical subjects

D L Haldeman

Publications and source records attributed to D L Haldeman.

4 recordsLinked to original sources

PubMed1997

Factors limiting microbial growth and activity at a proposed high-level nuclear repository, yucca mountain, nevada.

As part of the characterization of Yucca Mountain, Nev., as a potential repository for high-level nuclear waste, volcanic tuff was analyzed for microbial abundance and activity. Tuff was collected aseptically from nine sites along a tunnel in Yucca Mountain. Microbial abundance was generally low: direct microscopic cell counts were near detection limits at all sites (3.2 x 10(sup4) to 2.0 x 10(sup5) cells g(sup-1) [dry weight]); plate counts of aerobic heterotrophs ranged from 1.0 x 10(sup1) to 3.2 x 10(sup3) CFU g(sup-1) (dry weight). Phospholipid fatty acid concentrations (0.1 to 3.7 pmol g(sup-1)) also indicated low microbial biomasses; diglyceride fatty acid concentrations, indicative of dead cells, were in a similar range (0.2 to 2.3 pmol g(sup-1)). Potential microbial activity was quantified as (sup14)CO(inf2) production in microcosms containing radiolabeled substrates (glucose, acetate, and glutamic acid); amendments with water and nutrient solutions (N and P) were used to test factors potentially limiting this activity. Similarly, the potential for microbial growth and the factors limiting growth were determined by performing plate counts before and after incubating volcanic tuff samples for 24 h under various conditions: ambient moisture, water-amended, and amended with various nutrient solutions (N, P, and organic C). A high potential for microbial activity was demonstrated by high rates of substrate mineralization (as much as 70% of added organic C in 3 weeks). Water was the major limiting factor to growth and microbial activity, while amendments with N and P resulted in little further stimulation. Organic C amendments stimulated growth more than water alone.

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PubMed1994

Changes in Bacteria Recoverable from Subsurface Volcanic Rock Samples during Storage at 4 degrees C.

The abundance of viable microorganisms recovered from deep subsurface volcanic rock samples increased after rock perturbation and storage for 1 week at 4 degrees C, while the diversity and evenness of recoverable heterotrophic bacterial communities generally decreased. One sample of each morphologically distinct colony type, recovered both before and after storage of U12n rock samples, was purified and characterized by fatty acid methyl ester (MIDI) and API rapid NFT strips. As determined by MIDI cluster analysis, the composition of the recoverable microbial communities changed with storage of rock samples; some groups of organisms were recovered only before, only after, or at both sample times. In general, the isolates recovered only after storage of rock samples had a greater ability to utilize the carbohydrates included in API test strips and had faster generation times than isolates recovered only on initial plating. The nutritional versatility and faster growth rates of organisms recovered in higher proportions after sample storage provide evidence that some microbial community changes may be due to the proliferation of a few bacterial types. However, because some new genera are recovered only after storage, the possibility also exists that dormant bacterial types are resuscitated during sample perturbation and storage.

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PubMed1993

Diversity within a Colony Morphotype: Implications for Ecological Research.

Sets of bacterial isolates with the same colony morphologies were selected from spread plates of bacteria from deep subsurface rock samples; each set had a unique morphology. API-rapid-NFT analysis revealed that isolates within a set were the same. Fatty acid methyl ester analysis of one set of isolates clustered organisms within the same species, defining variation between isolates at the biotype (subspecies) and strain levels. Metal resistances consistently tracked with colony morphology, while antibiotic resistances were less reliable.

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PubMed1992

Comparison of Identification Systems for Classification of Bacteria Isolated from Water and Endolithic Habitats within the Deep Subsurface.

One water and three rock samples were taken from a mined tunnel system, U12n, in Rainier Mesa at the Nevada Test Site. Endolithic microorganisms were cultured from ashfall tuff, which was crushed and made into slurries with a formulation of artificial pore water, on R2A agar plates. Microbial counts ranged from 10 to 10 viable cells per g (dry weight) of rock sampled. The cultured water sample yielded 10 viable cells per ml. Many of the isolates were very small (<1 mum) when viewed in the rock matrix and remained small even when cultured. Most were gram-negative rods. Individual isolates were profiled by API-NFT strip number, antibiotic and metal resistance patterns, and colony and cellular morphologies. Three identification systems, API-NFT strips, BIOLOG, and MIDI, were compared. Each system identified only a small percentage of the total isolates, and in only seven cases were the isolates identified the same way by more than one system. The same genus was identified in three of these cases, but different species were indicated. The genus Pseudomonas was the most commonly identified. The isolate profiles and the three identification systems demonstrated that water isolates were considerably different from endolithic isolates.

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