Showing papers by "Thomas D. Brock published in 1975"

Salinity and the Ecology of Dunaliella from Great Salt Lake

Abstract: SUMMARY: Studies are reported on the distribution and salinity tolerances of populations of Dunaliella, a eucaryotic alga, in Great Salt Lake, Utah, U.S.A. This lake provides salinities varying from about 10% (w/v) NaCl to saturated (greater than 30% w/v). The alga is found throughout this salinity range, although population density varies markedly, mainly because of the influence of grazing animals in waters of low salinity. Enrichment cultures were set up using a range of salinities; at the lower salinities a wide variety of algae grew, but at the higher ones only Dunaliella was obtained. However, cultures derived from saturated brine and grown at salinities of around 25% (w/v) were not optimally adapted to these conditions, but grew and photosynthesized better in 10 to 15% (w/v) NaCl. A natural population from a saturated brine also had an optimum at a lower salinity than its habitat. It is concluded that although this eucaryotic alga is able to grow in saturated brine better than any other alga, it is not optimally adapted to these conditions and is apparently able to maintain populations at high salinity only because it meets no competition from other algae.

Effect of water potential on a microcoleus (cyanophyceae) from a desert crust1

Abstract: SUMMARY The effect of water potential, on the growth and photosynthesis of a species of Microcoleus forming a desert crust was determined, using both osmotic and matric variations in water potential. The alga was quite sensitive to moisture stress, partial inhibition of growth being observed at -7 bars, and complete inhibition at -18 bars. Photosynthesis was markedly inhibited at -18 bars, and virtually completely at, -28 bars (water potential of seawater) and lower. The alga was more sensitive to matric reduction in water potential than osmotic. By comparisons of these results with those obtained with other algae, it is concluded that this desert crust alga is not especially adapted to grow and photosynthesize at low water potentials, although it shows considerable ability to survive severe drought conditions.

Photosynthetic sulfide oxidation by Chloroflexus aurantiacus, a filamentous, photosynthetic, gliding bacterium.

Abstract: Chloroflexus, a newly described genus of filamentous, photosynthetic, gliding bacteria, oxidizes sulfide anaerobically under photoautotrophic or photoheterotrophic growh conditions and deposits elemental sulfur outside the cell. The formation of sulfur granules outside the cell supports the idea that this organism is related to the green sulfur bacteria (Chlorobiaceae).

Requirement of low oxidation-reduction potential for photosynthesis in a blue-green alga (Phormidium sp.).

Abstract: Photosynthesis in a Phormidium species which forms dense conical-shaped structures in thermal springs is strongly inhibited by aeration but is stimulated by sulfide and other agents (cysteine, thioglycolate, sulfite) which lower the oxidation-reduction potential. The compact structures which this alga forms in nature may restrict oxygen penetration from the environment so that the anaerobic or microaerophilic conditions necessary for photosynthesis can develop. The alga may be defective in a regulatory mechanism that controls the reoxidation of reduced pyridine nucleotides formed during photosynthesis. It is suggested that other mat-forming and benthic blue-green algae may also prefer anaerobic conditions for growth and photosynthesis.

Effect of water potential on growth and iron oxidation by Thiobacillus ferrooxidans.

Abstract: The effect of water potential on the growth of two strains of Thiobacillus ferroxidans was determined by adding defined amounts of sodium chloride or glycerol to the culture medium. The two strains differed slightly, and the most tolerant strain had a minimum water potential for growth of -15 to -32 bars when sodium chloride was used and -6 bars when glycerol was used. In another approach, the limiting water potential was determined by equilibrating small amounts of culture medium with atmospheres of relative humidities equivalent to specific water potentials, and the ability of the organism to grow and oxidize ferrous iron was determined. Under these conditions, which are analogous to those which might control water potential in a coal refuse pile or copper leaching dump, the lower limit at which iron oxidation occurred was -23 bars. The water potential of some coal refuse materials in which T. ferrooxidans was present were determined, and it was found that the water potentials at which the organism was active in these habitats were similar to those at which it was able to grow in culture. However, marked variation in water potential of coal refuse materials was found, presumably due to differences in clays and organic materials, and some coal refuse materials would probably never have water potentials at which the organism could grow. Some literature on the water potentials in copper leach dumps is reviewed, and it is concluded that control of water potential is essential to maximize the success of leaching operations. Because adequate drainage is necessary in a leach dump to ensure sufficient aeration, in many cases water availability in leach dumps may restrict the development of the bacterium necessary for the process.

Rate of Sulfuric-Acid Production in Yellowstone National Park

Abstract: Production of sulfuric acid in vapor-dominated hydrothermal systems is primarily a bacterial process. The rate of production of sulfuric acid was measured in springs in several acid-altered areas in Yellowstone National Park. Most of these springs lack surface water flow, but water enters and leaves these springs at approximately constant rates via underground seepage. The rate of water exchange in these steady-state systems was measured by enriching the springs with sodium chloride and measuring the rate at which the chloride ion was diluted. In all cases, the added chloride was diluted at an exponential rate, and half-times for dilution were calculated. The rate at which sulfuric acid was being produced was calculated from a knowledge of dilution rate and volume of the springs and from measurement of the sulfuric-acid concentrations of the waters. In several small springs, flow rate was measured more directly by draining the springs and measuring the rate at which water returned. These studies showed that water in acid springs enters as cold acid ground water, which is steam heated within the source pool. It was possible to estimate how much of the sulfuric acid in a given spring could have been produced in situ, and how much entered by underground seepage. In springs with pool volumes of 2,000 1 or less, most of the sulfuric acid was produced outside the spring, probably by bacteria present in the nearby acid-altered soil. In springs with pool volumes around 106 1, most of the sulfuric acid was produced in situ by resident bacterial populations. The techniques used may have wider utility in biogeochemical investigations.

The effect of water potential on photosynthesis in whole lichens and in their liberated algal components.

Abstract: Experiments were performed to determine whether the fungal component of the lichen thallus might enable the algal component to function under conditions of moisture stress at which it would be unable to function if free-living. Four lichens were used: Lepraria membranacea Ach., Cladonia submitis Evans, Usnea substerilis Mot. and Letharia vulpina (L.) Hue, collected from diverse geographical locations. Moisture stress was quantified using the water potential concept, and water potential was controlled both osmotically and matrically. The function of the alga was evaluated by measuring photosynthesis with a 14C technique. Photosynthesis of whole and ground lichen thalli was measured at different water potentials. Lowest water potentials permitting photosynthesis by whole lichen thalli ranged from-56 to-307 bar, and lowest potentials for the separated algal component ranged from-7 to-145 bar. In all cases the alga was able to photosynthesize at lower water potentials within the lichen thallus than when liberated. The grinding process did not harm the alga. It is suggested that one function of stored carbohydrate in the lichen fungus may be to increase internal osmotic pressure sufficiently so that the fungus thallus can absorb moisture from atmospheres of reduced humidity. If water secretion then occurred, some of this moisture could be made available to the alga.