Assessment of a new method in protist research: NanoSIMS analysis

Abstract

The hypereutrophic Lake Taihu in China was used as a model system for the development of a new

method in protist research. The possibilities and challenges of nanoscale secondary ion mass

spectrometry (NanoSIMS) analysis were assessed for the study of carbon transfer by protists. Lake

samples were incubated with 13C-labelled DIC (13C-NaHCO3) to study the uptake and transfer of carbon

in the Taihu food web. The NanoSIMS 50L instrument (Cameca) was used to measure stable carbon

isotope ratios in protists and the cyanobacteria Microcystis sp. Individual organisms were studied to

assess spatial heterogeneity within the cells. Precipitated crystals interfered with the signal of the

organisms. A way to remove crystals or to prevent crystal formation must be developed in the future.

Regions of interest were identified and analyzed. Significant differences were found between a light

and dark uptake experiment indicating the importance of autotrophs for the food web. 13C/(12C+13C)

values increased over the timepoints of the incubation experiment. The high 13C/(12C+13C) values of

protists indicated autotrophy. Although several challenges in the methodology remain, the NanoSIMS

approach was promising for single-cell analysis of protists.