The persistence of heavy metals (HMs) in the environment causes adverse effects to all living organisms; HMs accumulate along the food chain affecting different levels of biological organizations, from cells to tissues. HMs enter cells through transporter proteins and can bind to enzymes and nucleic acids interfering with their functioning. Strategies used by microalgae to minimize HM toxicity include the biosynthesis of metal-binding peptides that chelate metal cations inhibiting their activity. Metal-binding peptides include genetically encoded metallothioneins (MTs) and enzymatically produced phytochelatins (PCs). A number of techniques, including genetic engineering, focus on increasing the biosynthesis of MTs and PCs in microalgae. The present review reports the current knowledge on microalgal MTs and PCs and describes the state of art of their use for HM bioremediation and other putative biotechnological applications, also emphasizing on techniques aimed at increasing the cellular concentrations of MTs and PCs. In spite of the broad metabolic and chemical diversity of microalgae that are currently receiving increasing attention by biotechnological research, knowledge on MTs and PCs from these organisms is still limited to date.

Skeletonema comprises a planktonic genus of centric diatoms occurring in coastal and brackish waters worldwide. The most commonly reported species, Skeletonema costatum, was believed to be ubiquitous, morphologically plastic and euryhaline. Yet, recent studies showed that this perceived taxon consists of a series of species, including a more narrowly defined Skeletonema costatum sensu stricto. Here we investigated the effect of salinity on growth rate and cell morphology. Ten strains belonging to six Skeletonema species were incubated at salinities between 0 and 35; their growth response was measured and their cell morphology observed using light and electron microscopy. All strains grew well between salinities of 10 and 35, whereas the lowest salinity at which growth was observed differed among species and even within the same species: Skeletonema marinoi strains deriving from distinct environments (Baltic and North Sea) showed different lower tolerance limits. Two species, Skeletonema costatum and Skeletonema subsalsum, showed growth between salinities of 0 and 35 and exhibited very short intercellular processes when cultured in freshwater. Skeletonema subsalsum underwent cell enlargement when exposed to a salinity of 35.

The composition of photosynthetic pico and nanoeukaryotes was investigated in the North East Pacific and the Arctic Ocean with special emphasis on the Beaufort Sea during the MALINA cruise in summer 2009. Photosynthetic populations were sorted using flow cytometry based on their size and pigment fluorescence. Diversity of the sorted photosynthetic eukaryotes was determined using terminal-restriction fragment length polymorphism analysis and cloning/sequencing of the 18S ribosomal RNA gene. Picoplankton was dominated by Mamiellophyceae, a class of small green algae previously included in the prasinophytes: in the North East Pacific, the contribution of an Arctic Micromonas ecotype increased steadily northward becoming the only taxon occurring at most stations throughout the Beaufort Sea. In contrast, nanoplankton was more diverse: North Pacific stations were dominated by Pseudo-nitzschia sp. whereas those in the Beaufort Sea were dominated by two distinct Chaetoceros species as well as by Chrysophyceae, Pelagophyceae and Chrysochromulina spp.. This study confirms the importance of Arctic Micromonas within picoplankton throughout the Beaufort Sea and demonstrates that the photosynthetic picoeukaryote community in the Arctic is much less diverse than at lower latitudes. Moreover, in contrast to what occurs in warmer waters, most of the key pico- and nanoplankton species found in the Beaufort Sea could be successfully established in culture.