Betsy R. Robertson

University of Alaska Fairbanks, Fairbanks, AK, United States

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Publications (6)16.61 Total impact

  • D.K. Button, B.R. Robertson, Friedrich Jüttner
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    ABSTRACT: In Lake Zürich, a deep subalpine mesotrophic lake, phosphate was low or limiting at 0.2 to 1 μM relative to combined nitrogen at 50 μM. Heterotrophic bacteria were responsible for 53% of the observed microbial wet biomass in our depth profile while phytoplankton, largely Planktothrix (Oscillatoria) rubescens, contributed most of the remainder. Most cell carbon was contributed by this carbon-sufficient cyanobacterium. A material balance indicated that most of the phosphate was sequestered by the bacteria due to a higher phosphate content and specific affinity for this nutrient. Size distributions of the heterotrophic bacteria were narrow; 90% of organisms were from 0.06 to 0.06 μ3 in volume. Several subpopulations of bacteria were resolved by flow cytometry, and bivariate fluorescence (DAPI-DNA) and light scatter (cell-size) histogram profiles varied with depth. One or two of these subpopulations appeared to be bacteria with sufficient cytoplasmic constituents to produce a normal light-scatter signal but retained only a small amount of DNA; an apparent content of 200 kbp or 5% of a usual oligobacterial genome. These helped increase the oligobacterial population to 6 × 106 ml−1. Application of published specific affinities and measured nutrient concentrations to formulations of system kinetics led to the conclusion that growth rates of the heterotrophic bacterial fraction were carbon limited with cell size, and thus populations were controlled by grazing. The depth profile indicated that phototrophs affected concentrations in a significant way. Considerations of nutrient uptake kinetics suggested that much potential capacity remained in the dissolved phosphate pool to support additional phytoplanktonic biomass. Computations led to the conclusion that, if phosphate is generally limiting in lakes, then additional mechanisms exist which limit populations of phytoplankton to sufficiently small values to allow phosphate accumulation to observed levels. Bacterial biomass then depends on the organic carbon from these phosphate-controlled organisms.
    FEMS Microbiology Ecology 01/2006; 21(2):87 - 101. · 3.56 Impact Factor
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    ABSTRACT: A theory for solute uptake by whole cells was derived with a focus on the ability of oligobacteria to sequester nutrients. It provided a general relationship that was used to obtain the kinetic constants for in situ marine populations in the presence of naturally occurring substrates. In situ affinities of 0.9 to 400 liters g of cells(-1) h(-1) found were up to 10(3) times smaller than those from a "Marinobacter arcticus " isolate, but springtime values were greatly increased by warming. Affinities of the isolate for usual polar substrates but not for hydrocarbons were diminished by ionophores. A kinetic curve or Monod plot was constructed from the best available data for cytoarchitectural components of the isolate by using the theory together with concepts and calculations from first principles. The order of effect of these components on specific affinity was membrane potential > cytoplasmic enzyme concentration > cytoplasmic enzyme affinity > permease concentration > area of the permease site > translation coefficient > porin concentration. Component balance was influential as well; a small increase in cytoplasmic enzyme concentration gave a large increase in the effect of permease concentration. The effect of permease concentration on specific affinity was large, while the effect on K(m) was small. These results are in contrast to the Michaelis-Menten theory as applied by Monod that has uptake kinetics dependent on the quality of the permease molecules, with K(m) as an independent measure of affinity. Calculations demonstrated that most oligobacteria in the environment must use multiple substrates simultaneously to attain sufficient energy and material for growth, a requirement consistent with communities largely comprising few species.
    Applied and Environmental Microbiology 09/2004; 70(9):5511-21. · 3.95 Impact Factor
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    Garrett W. Pernèy, Betsy R. Robertson, D. K. Button
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    ABSTRACT: These protocols were developed for the quantitative analysis of DNA in aquatic bacteria and have been used to characterize both marine and freshwater samples and cultures (1). Apparent DNA content is a valuable tool when used in conjunction with forward light scatter for biomass (2–4) to characterize heterotrophic bacterioplankton, organisms which are too small for observation by light microscopy and difficult to cultivate (5).
    12/2003: pages 39-50;
  • Environmental Science and Technology 04/2002; 15(1). · 5.48 Impact Factor
  • Don K. Button, Betsy R. Robertson, Pham Quang
    Methods in Microbiology - METH MICROBIOL. 01/2001; 30:161-173.
  • D. K. Button, Betsy Robertson
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    ABSTRACT: Expanded specific affinity theory specifies the advantages of small dry mass and dilute cytoarchitecture in impoverished systems. For marine samples, bacterioplankton mean dry mass, according to flow cytometry, was near 24.5 fg cell-1. Conversion to volume with buoyant density gave a cell volume of 0.124 μm3. Total DNA was 2.9 fg cell-1. This compared with the size of a single genome of a small extinction-culture isolate, Sphingomonas sp. RB2256, of 3.96 fg or 3.6 Mb. The genome size of such isolates and other cultures decreased with metabolic simplicity. It was found that bacterioplankton could be exposed to radiolabeled amino acids and then sorted for size and that the specific affinities of the fraction of small organisms were as great as the fraction of large cells. Size, DNA, and metabolic-complexity distributions were concordant with the concepts that cell volume approaches a minimum set by sufficient space for the smallest genome that can provide sufficient information for competitive dissolved- nutrient acquisition, and that space requirements are further alleviated by the expression of few cytoplasmic-enzyme molecules in each of the various pathways and a dilute cytoplasm. Bacterioplankton approached a minimum genome size of 1.7 Mb with a minimum cell volume of about 0.06 μ m3 and a DNA content of 16% dry weight. The property of small dry mass with a low DNA content was common in in situ bacteria but absent from cultivated representatives, which led to speculation that failure to grow in the laboratory is related to missing regulatory information.
    Limnology and Oceanography 01/2000; 45(2):499-505. · 3.62 Impact Factor