Probing the evolution, ecology and physiology of marine protists using transcriptomics.

Protists, which are single-celled eukaryotes, critically influence the ecology and chemistry of marine ecosystems, but genome-based studies of these organisms have lagged behind those of other microorganisms. However, recent transcriptomic studies of cultured species, complemented by meta-omics analyses of natural communities, have increased the amount of genetic information available for poorly represented branches on the tree of eukaryotic life. This information is providing insights into the adaptations and interactions between protists and other microorganisms and macroorganisms, but many of the genes sequenced show no similarity to sequences currently available in public databases. A better understanding of these newly discovered genes will lead to a deeper appreciation of the functional diversity and metabolic processes in the ocean. In this Review, we summarize recent developments in our understanding of the ecology, physiology and evolution of protists, derived from transcriptomic studies of cultured strains and natural communities, and discuss how these novel large-scale genetic datasets will be used in the future.

Effects of Ag nanoparticles on survival and oxygen consumption of zebra fish embryos, Danio rerio.

Ultrafine silver (Ag) particles, defined as having one dimension in 1-100 nanometer (nm) size range, pose a unique threat to aquatic ecosystems due to their wide use in the healthcare and commercial industries. Previous studies have demonstrated some consequences of nanosilver exposure for earlier life stages of aquatic organisms, but few focus on the effects on metabolic processes such as oxygen consumption. Additionally, few authors have tackled the issue of how size, shape and composition of nanosilver particles are important in determining their level of bioactivity and biodistribution in the aquatic environment. In this study, embryos of the zebra fish, Danio rerio, (n = 2373) were exposed to varying concentrations of two Ag particle sizes, 12 and 21 nm, at time points 24 and 48 h after fertilization. The 12 nm particles were found to be more bioactive with a lethal dose 50 (LD(50)) concentration of 15.8 µg/mL compared to 50.1 µg/mL for 21 nm particles. The effective dose level (ED) was measured as 12.6 µg/mL for the 12 nm particles and 5.0 µg/mL for the 21 nm particles. Using survival curves, we found that in terms of number of particles in suspension, 21 nm particles have a greater impact on survival than 12 nm particles. Our measured respiration rates for 24 and 48 h embryos (n = 528) exposed to 0 0.02-0.14 mg/mL Ag showed no active upregulation of an energetically expensive detoxification pathway at this early point in development. Results from this study illustrate that advancements in the development of environmentally friendly nanoparticles can only occur if there is continued research to identify the most bioactive characteristics of these metallic particles.