Exploring strategies for nanoflagellates living in a ‘wet desert’

Abstract

We investigated the survival strategies and the competitive strength of pigmented and colourless bacterivorous flagellates using 2 model organisms, the bacterivorous chrysophytes Poterioochromonas malhamensis and Spumella sp., fed small ultramicrobacteria (0.044 µm 3) and large bacteria (0.38 µm 3 ). The numerical responses indicated that small bacteria are not such a good food source as large bacteria, even when bacterial cell volume was taken into account. The growth rates of the heterotrophic Spumella sp. exceeded those of the mixotrophic P. malhamensis at high bacterial concentrations of both sizes of bacteria. At very low prey abundances, P. malhamensis grew better than Spumella sp., mainly because the mortality rate of the latter was very high. At bacterial biovolumes encountered in oligotrophic/mesotrophic lakes, the growth curves of the 2 flagellates intersected. Although P. malhamensis possesses a chloroplast, growth of cultures incubated in the light and the dark did not differ even at very low prey concentrations, indicating that photosynthesis plays a minor role for this chrysophyte. Experiments carried out with mixed flagellate cultures showed that P. malhamensis ingested Spumella sp. cells. Applying our data to natural abundances of small and large bacteria as well as pico/nanoplankton we could demonstrate that P. malhamensis is a K-strategist. Large bacteria made up the major portion of its carbon uptake, but small bacteria, pico-nanoplankton and (to a minor extent) photosynthesis also contributed to its gross carbon uptake, indicating a broad use of different resources by this species. Spumella sp. is more of an r-strategist and relies mainly on large bacteria for growth although small bacteria can contribute significantly to its diet.

Ecomicrobiology and microbial assimilative capacity of the oligotrophic Andean Lake Laja, Chile

“…Compared to cell sizes estimated for lake bacteria (summarized by Jugnia et al 1998) this average cell volume is in most cases lower than the minimum values of other lakes. With this size, the bacterioplankton made up solely ultramicrobacteria defi ned with a volume of < 0.05 µm 3 (Boenigk et al 2006) and < 0.1 µm 3 (Schut et al 1997, Hahn et al 2003, respectively. Here a frequency of bacterial cell volumes of < 0.05 µm 3 cell -1 = 77 % and < 0.1 µm 3 cell -1 = 96 %, respectively was estimated.…”

Stuck in the mud: suspended sediments as a key issue for survival of chrysomonad flagellates

“…Growth rates for strain JBM10 were taken from Boenigk et al (2006). These growth rates were obtained in a similar way as for the flagellate strain JBC07.…”

“…Clearance rates in the presence of a constant (A) suspended particle load of 10 mg l -1 and (B) suspended particle abundance of 1.49 × 10 7 particles ml -1 . Horizontal straight line represents the clearance rate of the control treatment without particles, and the dotted lines the respective standard deviation ilar to those of the flagellate strain JBM10 (Boenigk et al 2006). However, in the second set of experiments, i.e.…”

“…The discrepancy between these studies again highlights the importance of natural food concentrations and food particle size for estimating the effect of abiotic parameters on the growth of Spumella-like flagellates (cf. Boenigk et al 2006).…”

“…3). Growth rates of the flagellate strain JBM10 growing on the bacteria CB5 and MWHMoNR1 are provided in Boenigk et al (2006).…”