Activity and Characteristics of the Dissolved Organic Carbon-Dependent Picoplankton over the Annual Cycle in a Subarctic Lake

点击翻译按钮获取中文摘要

ABSTRACT ButtonOPP-0243913The Principal Investigator will make in situ measurements made throughout the annual cycle in a near arctic lake where photosynthesis rates vary from zero to 500 mg C/m2 per day due to large changes in sun angle and snow cover. The work will focus on changes in the bacterioplankton over the winter/summer transition. Bacterial activity will be determined by substrate uptake, usually an amino acid mixture. Measurements will include artificial warming and cooling to determine activation energies from which temperature preferences are evaluated. Incubations will include an auxiliary substrate such as glucose to help determine the energization state of organisms in the collected sample. These activation energies are determined in conjunction with membrane potential measurements of the individual cells by flow cytometry. Companion measurements will be cell population and mass by flow cytometry for calculating specific affinities. The distribution of cell mass and DNA/cell is used as a further index of organism activity over the seasons. Cell yields from substrate consumed over the seasons will be used to help determine productivity and endogenous requirements, particularly during winter. These are linked to dissolved free amino acid concentrations as an indication of labile organic substrates. Further characterization will be by DNA fragment and sequence analyses. Existing culture collections of isolates will be further developed with the objective of finding and characterizing a typical low DNA, small, typical freshwater oligobacterium for physiological study. Cultures are used to determine values for missing terms in specific affinity theory such as the size of thresholds for substrate uptake and the concentration of transported substrate in cytoplasmic pools. Expanded statistical theory for testing cell-cell interactions will be applied with the objective of improving the small (1%) culturability presently attained. This work involves the application of novel theory and methods to the understanding of microbial processes in the Arctic with particular reference to seasonal changes in water temperature. These will serve to improve estimates of bacterial activity and productivity. Novel extinction culture procedures coupled with new statistical and kinetic theory can help solidify the sparse understanding of one of our largest forms of active living material. Developing kinetic theory is beginning to alter paradigms, as is quantitative flow cytometry together with nutrient flux calculations, and is thereby altering perceptions of oligobacterial physiology. The novel technology will be extended to a wide cross section of students through graduate and undergraduate courses and seminars. The broader impacts of the work include the development of novel concepts, such as ways of linking aspects of the carbon and nutrient cycle to organism activity, physiology, nutrient concentrations, and temperature. Developments in component technologies, such as quantitative flow cytometry and extinction culturing, are applicable to microbiology in general. Most importantly the work will provide a mechanistically competent alternative to the Michaelis Menten paradigm to improve description and comparison of microbial activity and dynamics.