Dynamic Properties of Picoplankton Over the Annual Cycle in Near-Polar Lakes

点击翻译按钮获取中文摘要

9907776Button This project will examine the dynamic properties of picoplankton over the annual cycle in near-polar lakes. Investigations will focus on describing typical bacterial species from a near-arctic freshwater system during the severe transition in primary productivity and temperature, infer the presence of key organics in theirmaintenance, and quantify the contribution of these mostly undescribed organisms to carbon dioxide production rates. The study site, Harding Lake, is known to have a relatively stable bacterial biomass over the annual cycle. However physical properties of the bacteria, DNA distributions, kinetic constants and associated amino acid concentrations and primary productivities varydramatically between summer and winter. Focus is on the predominatecultivation-resistant bacteria with attention to the small low-DNA forms. Thesewill be isolated and probed for their activity and ability to utilize variouscarbon sources including those expected from the hydrolysis of plant material. A number of novel approaches will be used. These include recently perfectedmeasures of population, biomass per cell, cell volume, DNA content, and genome size by flow cytometry. A chromosome-ratio method for growth rate will be verified at low values, temperature corrections reevaluated, and the method used as a probe of in situ rates of growth with verification by dilution culture.DAPI-DNA assays will be corrected for A+T bias by simultaneously evaluating G+C content of individual bacteria, thereby improving subpopulation resolution.Additional single-cell activity probes include RNA, reducing power and membrane potential for following activity in dilution cultures and more thoroughlycharacterizing in situ populations over the annual cycle. Extinction culturesthat depend on naturally produced sources of carbon are used to isolate bacteriawithout bias toward large fast-growing forms. Cultures are partitioned againstraw lakewater through diffusion membranes to improve culturability. Data areused to determine viabilities as well as the number of species present byincorporating novel formulae as well as DGGE techniques to identify the numberof species in developing populations. Useful carbon sources are evaluatedaccording to flow cytometry patterns from the extinction cultures followingnutrient amendments. Substrates used are taken as an indication of those present and kinetic measurements suggest their concentrations. Ability to use substrates at small concentrations is compared directly according to specific affinity and oligotrophic capacity as recently defined. Isolated species are identified by 16-S ribosomal RNA analysis, and in situ carbon dioxide evolution is calculated from growth rates according to the active (total less very low-DNA) biomass and associated rates of growth. Temperature effects on both uptake and growth are evaluated without carbon-source amendment to determine if rates at low temperatures collapse, or if sufficient membrane potential is sustained tomaintain the required specific affinities.