Quantitative Proteomics Reveals Ecophysiological Effects of Light and Silver Stress on the Mixotrophic Protist Poterioochromonas malhamensis

Abstract

Aquatic environments are heavily impacted by human activities including climate warming and the introduction of xenobiotics. Due to the application of silver nanoparticles as bactericidal agent the introduction of silver into the environment strongly has increased during the past years. Silver ions affect the primary metabolism of algae, in particular photosynthesis. Mixotrophic algae are an interesting test case as they do not exclusively rely on photosynthesis which may attenuate the harmful effect of silver. In order to study the effect of silver ions on mixotrophs, cultures of the chrysophyte Poterioochromonas malhamensis were treated in a replicate design in light and darkness with silver nitrate at a sub-lethal concentration. At five time points samples were taken for the identification and quantitation of proteins by mass spectrometry. In our analysis, relative quantitative protein mass spectrometry has shown to be a useful tool for functional analyses in conjunction with transcriptome reference sequences. A total of 3,952 proteins in 63 samples were identified and quantified, mapping to 4,829 transcripts of the sequenced and assembled transcriptome. Among them, 720 and 104 proteins performing various cellular functions were differentially expressed after eight days in light versus darkness and after three days of silver treatment, respectively. Specifically pathways of the energy and primary carbon metabolism were differentially affected by light and the utilization of expensive reactions hints to an energy surplus of P. malhamensis under light conditions. The excess energy is not invested in growth, but in the synthesis of storage metabolites. The effects of silver were less explicit, observable especially in the dark treatments where the light effect could not mask coinciding but weaker effects of silver. Photosynthesis, particularly the light harvesting complexes, and several sulphur containing enzymes were affected presumably due to a direct interference with the silver ions, mainly affecting energy supply.

Evolution of heterotrophy in chrysophytes as reflected by comparative transcriptomics

“… 2015 ; Beisser et al . 2017b ). As shifts in the prevailing mode of nutrition usually require more than 24 h, a switch of nutritional mode within mixotrophs is no subject of a diurnal variation (Sanders, Porter and Caron 1990 ).…”

TaxMapper: an analysis tool, reference database and workflow for metatranscriptome analysis of eukaryotic microorganisms

“…On the functional level a test for differential expression reveals 34 KEGG orthologous genes that differ significantly (FDR <0.1) between the two groups and show an enrichment of photosynthesis pathways. It is known that silver ions affect the primary metabolism in particular photosynthesis by direct interference [ 53 , 56 ]. On the other hand, it has been shown that for low concentrations of silver green algae grows is increased as observed in Fig.…”

TaxMapper: An Analysis Tool, Reference Database and Workow for Metatranscriptome Analysis of Eukaryotic Microorganisms

“…On the functional level a test for differential expression reveals 34 KEGG orthologous genes that differ significantly (FDR < 0.1) between the two groups and show an enrichment of photosynthesis pathways. It is known that silver ions affect the primary metabolism in particular photosynthesis by direct interference [52,53]. On the other hand, it has been shown that for low concentrations of silver green algae grows is increased as observed in Figure 7 A [54].…”