J. Robie Vestal

Lipid analysis in microbial ecology: quantitative approaches to the study of microbial communities.

n nature, microorganisms rarely exist as monocultures, but live in communities with other microbes. These communities play an important role in the biosphere, primarily in recycling biologically important elements. All the essential biochemical cycles of carbon, hydrogen, nitrogen, oxygen, and sulfur are mediated by communities of microorganisms. Consequently, understanding what microbes in a natural environment are doing, rather than simply which microbes are present, is important to understanding their role within ecosystems. Analytical techniques developed in the last decade offer insights into the nature of these important ecosytem components. Microbial communities include viruses, eubacteria, archaebacteria, fungi, protozoa, micrometazoa, and algae (Margulis et al. 1986). The communities exist throughout the biosphere and even occupy such extreme environments as boiling-hot springs (Brock 1978); the deep sea at high hydrostatic pressure (ca. 1200 atmospheres; Jannasch and Taylor 1984); the cold deserts of Antarctica in the pore spaces of sandstone (Friedmann 1982); deep subsurface Analytical techniques developed in the last decade offer insights into these important

Transformation of a Tundra River from Heterotrophy to Autotrophy by Addition of Phosphorus

Continuous enrichment of an arctic river with only 10 parts per billion phosphate-phosphorus caused an immediate growth of attached algae for more than 10 kilometers downstream, showing that phosphorus alone limited photosynthesis. As a result of the increased photosynthesis, there was an increase in bacterial activity in films on rocks on the bottom of the stream. The major source of energy became the photosynthetic carbon fixed in the stream rather than the organic material entering from the surrounding tundra, and the overall metabolism of the stream shifted from heterotrophy to autotrophy. An increase in the size and developmental stage of some of the dominant aquatic insects illustrates the food limitation in this nutrient-poor habitat.

Nutrient Incluence on a Stream Grazer: Orthocladius Microcommunities Respond to Nutrient Input

A whole—stream enrichment experiment of phosphorus and, further down—stream, of phosphorus and nitrogen, allowed us to examine the growth and density responses of the tube—building larval chironomid Orthocladius rivulorum to nutrient enrichment of the Kuparuk River in arctic Alaska, and to evaluate nutrient effects on the tube microbial community. The larva feeds by grazing a diatom monoculture of Hannaea arcus from the tube exterior, thus direct nutrient effects on the tube microbiota may translate into indirect nutrient effects on the larva. Electron microscopy indicated that tube silk was formed into a sheet, with a filamentous substructure that repeated at 50—nm intervals. Bacterial micro—colonies occurred at the points where the erect diatoms were attached to the silk. Microbial activity of Orthocladius tubes in the P—fertilized section was 2—3 times that of the control section of the river, and total microbial biomass in the P—fertilized section was 3—4 times that of the control section. Chlorophyll a was also higher on Orthocladius tubes downstream of both P and N + P fertilization sites. However, the rate of biomass accumulation on tubes was more rapid downstream of N + P addition, suggesting primary P and secondary N limitation of the rate of primary production in the river. Chlorophyll a was higher on tubes than on rocks or experimental tiles, which indicated that tubes were a more favorable algal habitat for Hannaea. Pupal tubes had less chlorophyll a than larval tubes, suggesting that larval activity may have contributed to the higher algal biomass on tubes. Orthocladius benefitted from the enhanced tube flora; larvae grew larger in the fertilized sections of the stream than in the upstream sections. The results suggest that Orthocladius with its tube and associated biota function as microcommunities that respond directly and indirectly to the surrounding nutrient regime, but have considerable trophic independence from surrounding portions of the epilithon. They may constitute 12—43% of total epilithic algal biomass.

Biogeochemistry of oxalate in the antarctic cryptoendolithic lichen-dominated community

Cryptoendolithic (hidden in rock) lichen-dominated microbial communities from the Ross Desert of Antarctica were shown to produce oxalate (oxalic acid). Oxalate increased mineral dissolution, which provides nutrients, creates characteristic weathering patterns, and may ultimately influence the biological residence time of the community. Oxalate was the only organic acid detectable by HPLC, and its presence was verified by GC/MS. Community photosynthetic metabolism was involved in oxalate production since rates of 14C-oxalate production from 14C02 were higher in light than in dark incubations. Flaking of the sandstone at the level of the lichen-dominated zone a few millimeters beneath the rock surface can be explained by dissolution of the sandstone cement, which was enhanced by Si, Fe, and Al oxalate complex formation. Added oxalate was observed to increase the solubility of Si, Fe, Al, P, and K. Oxalates ability to form soluble trivalent metal-oxalate complexes correlated with the observed order of metal oxide depletion from the lichen-dominated zone (Mn > Fe > Al). Thermodynamic calculations predict that Fe oxalate complex formation mobilizes amorphous Fe oxides (ferrihydrite) in the lichen-dominated zone, and where oxalate is depleted, ferrihydrite should precipitate. Hematite, a more crystalline Fe oxide, should remain solid at in situ oxalate concentrations. Oxalate was not a carbon source for the indigenous heterotrophs, but the microbiota were involved in oxalate mineralization to CO2, since oxalate mineralization was reduced in poisoned incubations. Photooxidation of oxalate to C02 coupled with photoreduction of Fe(Ill) may be responsible for oxalate removal in situ, since rates of 14C-oxalate mineralization in dark incubations were at least 50% lower than those in the light. Removal of oxalate from Si, Fe, and Al complexes should allow free dissolved Si, Fe, and Al to precipitate as amorphous silicates and metal oxides. This may explain increased siliceous crust (rock varnish or desert varnish) formation near the surface of colonized rocks were light intensity is greatest.

The Limnology of Toolik Lake

The scientific study of the Arctic is recent with the exception of various collections and cataloging of plants and animals in the 19th century. The limnological investigation of the Arctic is even more recent with the first review paper of arctic limnology listing only seven papers that dealt with arctic lakes (Rawson, 1953). However, after World War II, research stations developed in arctic Europe, Greenland, and at Point Barrow in Alaska. There was considerable research activity at the Naval Arctic Research Laboratory (NARL) in Barrow (Livingstone et al., 1958; Hobbie, 1964, Chapter 2; Stross and Kangas, 1969), much of which is reviewed by Hobbie (1973).

The Kuparuk River: A Long-Term Study of Biological and Chemical Processes in an Arctic River

Our studies have focused on carbon and nutrient dynamics, primary productivity and decomposition, and abundance and life histories of the macroconsumers in the Kuparuk River in arctic Alaska. The overall objective of these studies is to understand the processes controlling primary and secondary productivity, nutrient dynamics, and trophic structure.

A comparison of double vial to serum bottle radiorespirometry to measure microbial mineralization in soils

Abstract Two methods of measuring mineralization rates were compared for their ability to quantify the microbiol mineralization of organic compounds in soils. In each of three soils used, the serum bottles gave higher yields for the mineralization of both [ 14 C]glucose and [ 14 C]cellulose (lignocellulose) than the double vials. In two of the soils, the serum bottles also showed less variation between replicates than the double vials. Furthermore, the mineralization of glucose in the serum bottles fit a first order rate model, whereas the mineralization of glucose in the double vials showed best fit to a linear model. Results using different amounts of soils indicated that container geometry may have placed unfavorable restrictions upon the double vial system, lowering the yield of 14 CO 2 from the soils. Therefore, the serum bottle method was found to be the better method for measuring mineralization rates in soils.

Phosphorous limitation in an arctic river biofilm—A whole ecosystem experiment

Abstract A fourth-order arctic river was experimentally enriched with phosphate (7.7 ± 7.0 μ g 1−1) to determine the effect of such a loading (equivalent to a community of 10,000 people) upon the trophically important biofilm. The effect upon a light-grown biofilm (an autotrophic/heterotrophic assemblage) and a dark-grown biofilm (predominantly heterotrophic assemblage) was determined after 28 days of colonization. Seven attributes of the biofilms were monitored, 2 autotrophic indices, chlorophyll α, [14C]HCO3 incorporation into lipids and 5 heterotrophic indices; [14C]acetate incorporation into lipids, metabolic heat output, turn-over times of microbially labile glucose and glutamate and mineralization of microbially recalcitrant ring-labelled [14C]hydroxybenzoic acid. The findings showed that the addition of phosphorus resulted in a substantial stimulation of both autotrophic and heterotrophic processes suggesting that arctic rivers of this type would be liable to cultural eutrophication.

Effects of Prudhoe bay crude oil on primary production and zooplankton in arctic tundra thaw ponds

Abstract The effects of Prudhoe Bay, Alaska, crude oil on the indigenous phytoplankton and zooplankton of tundra thaw ponds were studied under controlled conditions in situ during the summer of 1976. These effects were compared with uncontrolled oil spills on Pond Omega (a year previously) and Pond E (six years previously). In the uncontrolled spills, the phytoplankton species composition of both ponds remained appreciably different compared with control Pond C, although phytoplankton biomass did not differ greatly. Primary production remained low in Pond Omega but had recovered to control levels in Pond E. In controlled subpond experiments, oil caused a decrease of about 90–100% in primary production in five days but recovered to 40–50% of the control level within fifteen days. During that time, phytoplankton biomass decreased initially but recovered within fifteen days. Oil caused a shift in phytoplankton species composition from a predominance of cryptophytes to chrysophytes. Subponds containing two Daphnia middendorffiana and one Brachinecta paludosa per litre of pondwater were also affected by oil, causing zooplankton death within three or four days. After that time, changes in the phytoplankton species composition were similar to control subponds without zooplankton. Oil toxicity to zooplankton or experimental removal resulted in a loss of grazing pressure which caused the elimination of the cryptophyte Rhodomonas sp. This species was still absent from Pond Omega, but was seen in Pond E for the first time, when zooplankton also reappeared after six years. Oil perturbation of tundra thaw ponds causes a loss of zooplankton and a reduction in primary production. Phytoplankton primary production recovers somewhat but algal species composition remains changed because of the loss of zooplankton grazing pressure and the selective effects of oil.

Survival of microorganisms in smectite clays: implications for Martian exobiology.

Manned exploration of Mars may result in the contamination of that planet with terrestrial microbes, a situation requiring assessment of the survival potential of possible contaminating organisms. In this study, the survival of Bacillius subtilis, Azotobacter chroococcum, and the enteric bacteriophage MS2 was examined in clays representing terrestrial (Wyoming type montmorillonite) or Martian (Fe(3+)-montmorillonite) soils exposed to terrestrial and Martian environmental conditions of temperature and atmospheric pressure and composition, but not to UV flux or oxidizing conditions. Survival of bacteria was determined by standard plate counts and biochemical and physiological measurements over 112 days. Extractable lipid phosphate was used to measure microbial biomass, and the rate of 14C-acetate incorporation into microbial lipids was used to determine physiological activity. MS2 survival was assayed by plaque counts. Both bacterial types survived terrestrial or Martian conditions in Wyoming montmorillonite better than Martian conditions in Fe(3+)-montmorillonite. Decreased survival may have been caused by the lower pH of the Fe(3+)-montmorillonite compared to Wyoming montmorillonite. MS2 survived simulated Mars conditions better than the terrestrial environment, likely due to stabilization of the virus caused by the cold and dry conditions of the simulated Martian environment. The survival of MS2 in the simulated Martian environment is the first published indication that viruses may be able to survive in Martian type soils. This work may have implications for planetary protection for future Mars missions.