Bacterial biomass and cell size distributions in lakes: More and larger cells in anoxic waters

Abstract

We measured bacterial abundance, cell size distribution, and related microbiological and geochemical parameters in 20 stratified lakes from three regions in the U.S. Both largest cell size and greatest bacterial abundance occurred in anoxic waters. Bacterial size distributions from the hypolimnia of lakes that were oxic were identical to those in surface waters. Bacteria from anoxic hypolimnia were 2-10 times larger than those from oxic water and cell size was independent of temperature under either oxic or anoxic conditions. For all lakes and strata, bacterial abundance was strongly related to the concentration of total phosphorus (TP). Cell size was not related to TP or to bacterial abundance, suggesting that abundance and size may be regulated by different processes. Bacterial biomass (calculated from the product of mean cell size and bacterial abundance) was typically 4 times greater in anoxic than in oxic waters of lakes.

Toward a mechanistic understanding of how natural bacterial communities respond to changes in temperature in aquatic ecosystems

“…To reflect this, we used a Droop-style model to allow for a variable biomass stoichiometry and also to allow resource uptake to vary in relation to the changing cell quota of that resource. In addition, we allow for differences in minimal phosphorus quota (Q P min ) between cold-adapted and warm-adapted species by allowing the warm-adapted species to have a lower minimal phosphorus cell quota (Q P min ) than the cold-adapted species (Box 4), consistent with work from previous research including our own (Cole et al, 1993;Nishimura et al, 2005;Cotner et al, 2006). An advantage of including these biologically tenable biomass dynamics is that it also allows us to evaluate the role of bacteria as recyclers or sinks of limiting nutrients across thermal gradients.…”

“…Also larger cells, indicative of higher nutrient content, have been associated with cold hypolimnetic waters (Cole et al, 1993). Here we modeled the cold-adapted species to have higher Q P min than warm-adapted species (Box 4).…”

“…Also larger cells, indicative of higher nutrient content, have also been associated with cold hypolimnetic waters (Cole et al, 1993) and cells grown in culture were shown to have increasing P requirements at lower temperatures when growth rate was held constant (Cotner et al, 2006). Therefore, we modeled cold-adapted species to have higher Q P min than warm-adapted species.…”

Lake Kauhako-, Moloka'i, Hawai'i: biological and chemical aspects of a morpho-ectogenic meromictic lake

“…The fact that heterotrophic bacterial numbers were high in anoxic water above the pycnocline suggests a switch to nitrate respiration (Overbeck 1993). Chroococcoid cyanobacteria similar to those described here as 'Synechococcus'-like are found in lakes (Cole 1983) and oligotrophic seawaters (Campbell & Vaulot 1993). In Lake Kauhaki5, large 'Synechococcus'-like unicells, together with an unidentified filamentous cyanobacterium, dominated the picophytoplankton in the upper 2 m. Water samples from 4.5 to 4.75 m appeared brown, a coloration that may have arisen from brown pigmented Chlorobium spp.…”

“…As the combined heterotrophic and autofluorescent Bacteria cell numbers increased 2.75-fold from 3 to 4.5 m it is likely that the TOC concentration increased at the pycnocline, especially since bacterial cells in anoxic lake waters may be larger than in oxic waters (Cole et al 1993). Heterotrophic and photosynthetic activities in surface waters of Lake KauhakG probably keep NH,' and SRP low and maintain rapid turnover rates.…”