Small Players, Large Role: Microbial Influence on Biogeochemical Processes in Pelagic Aquatic Ecosystems

Nutrient and light availability regulate the relative contribution of autotrophs and heterotrophs to respiration in freshwater pelagic ecosystems

“…Although competition between bacteria and phytoplankton for dissolved nutrients is likely to play a large role in explaining why oligotrophic ecosystems tend to have higher bacteria : phytoplankton biomass and activity, other hypotheses (not addressed in this study) have also been proposed (see Cotner and Biddanda [2002] for a recent review). Some have argued that the observed decrease in bacterial biomass and activity with increasing trophic state is a result of increases in the consumption of bacterial biomass by protozoan grazers (e.g., Sanders et al 1992).…”

“…Heterotrophic bacteria often account for a large proportion of inorganic nutrient (PO 4 Ϫ and NH 4 ϩ ) uptake in both freshwater and marine ecosystems (Currie 1990;Kirchman 1994) at low ambient nutrient concentrations. Heterotrophic bacteria and other small cells have a higher surface-to-volume ratio than eukaryotic phytoplankton cells resulting in a higher affinity (lower apparent half-saturation constant, K m ) for inorganic nutrient uptake (Cotner and Biddanda 2002). There is a growing consensus that bacteria have a higher P content (lower C : P) than phytoplankton (Vadstein et al 1989;Sterner and Elser 2002).…”

“…While the high surface-to-volume ratio of bacteria results in a high affinity for nutrients, the small cell size leads to little capacity for storing nutrients internally. In contrast, phytoplankton are expected to sequester an increasing fraction of available nutrients with increasing trophic state as a result of their larger cell size (Cotner and Biddanda 2002). Several studies have demonstrated that the ability of phytoplankton to take up P and accumulate higher intercellular P levels is either comparable (Vadstein et al 1989) or superior to the ability of bacteria (Suttle et al 1990;Cotner and Wetzel 1992;Thingstad et al 1993).…”

“…Irradiance level, Chl a, and DOC concentrations and planktonic community respiration (CR), bacterial respiration (BR), bacterial contribution to planktonic community respiration (BR : CR), and phytoplankton respiration (PR) for the experimental systems studied in the three light-nutrient interaction experiments. quire an increased fraction of the available nutrients as nutrient availability increases (Suttle et al 1987;Cotner and Biddanda 2002). Under such conditions, the nutrient uptake capacity of small bacterial cells is likely to become saturated.…”

Detection of UVBR-sensitive and -tolerant bacteria in surface waters of the western North Pacific

“…Exposure to solar UV radiation (UVR) can reduce biological productivity, affect reproduction, and increase mutation rate in microorganisms, macroalgae, eggs, larval stage of fish, and other aquatic animals [1]. Aquatic bacteria, which are a major component of aquatic ecosystems and play a key role in biogeochemical processes such as nutrient cycling [2], are also sensitive to solar UVR, especially biologically harmful UVBR because of their lack of pigments, small cell size and short generation time [3,4].…”