High-throughput single-cell analysis is a challenging task. Label-free tomographic phase microscopy is an excellent candidate to perform this task. However, in-line tomography is very difficult to implement in practice because it requires a complex set-up for rotating the sample and examining the cell along several directions. We demonstrate that by exploiting the random rolling of cells while they are flowing along a microfluidic channel, it is possible to obtain in-line phase-contrast tomography, if smart strategies for wavefront analysis are adopted. In fact, surprisingly, a priori knowledge of the three-dimensional position and orientation of rotating cells is no longer needed because this information can be completely retrieved through digital holography wavefront numerical analysis. This approach makes continuous-flow cytotomography suitable for practical operation in real-world, single-cell analysis and with a substantial simplification of the optical system; that is, no mechanical scanning or multi-direction probing is required. A demonstration is given for two completely different classes of biosamples: red blood cells and diatom algae. An accurate characterization of both types of cells is reported, despite their very different nature and material content, thus showing that the proposed method can be extended by adopting two alternate strategies of wavefront analysis to many classes of cells.

Some marine diatoms negatively affect the reproduction of dominant zooplankton grazers such as copepods, thus compromising the transfer of energy through the marine food chains. In this paper, the metabolic mechanism that leads to diatom-induced toxicity is investigated in three bloom-forming microalgae. We show that copepod dysfunctions can be induced by highly reactive oxygen species (hROS) and a blended mixture of diatom products, including fatty acid hydroperoxides (FAHs); these compounds display teratogenic and proapoptotic properties. The process is triggered by the early onset of lipoxygenase activities that elicit the synthesis of species-specific products, the basic structures of which were established (1-20); these compounds boost oxidative stress by massive lipid peroxidation. Our study might explain past laboratory and field results showing how diatoms damage zooplankton grazers even in the absence of polyunsaturated aldehydes, a class of molecules that has been formerly implicated in mediating the toxic activity of diatoms on copepods.

Oxylipins are important signal transduction molecules widely distributed in animals and plants where they regulate a variety of events associated with physiological and pathological processes. The family embraces several different metabolites that share a common origin from the oxygenase-catalyzed oxidation of polyunsaturated fatty acids. The biological role of these compounds has been especially studied in mammalians and higher plants, although a varied and very high concentration of these products has also been reported from marine macroalgae. This article gives a summary of our results concerning the oxylipin chemistry of marine diatoms, a major class of planktonic microalgae that discourage predation from their natural grazers, zooplanktonic copepods, using chemical warfare. These apparently harmless microscopic cells produce a plethora of oxylipins, including short-chain unsaturated aldehydes, hydroxyl-, keto-, and epoxyhydroxy fatty acid derivatives, that induce reproductive failure in copepods through abortions, congenital malformations, and reduced larval growth. The biochemical process involved in the production of these compounds shows a simple regulation based on decompartmentation and mixing of preexisting enzymes and requires hydrolysis of chloroplast-derived glycolipids to feed the downstream activities of C16 and C20 lipoxygenases.

BackgroundDiatoms are an ecologically relevant group of microalgae that are not commonly considered for bio-oil production even if they are responsible for massive blooms at sea. Seventeen diatom species were screened for their capacity to produce biomass and lipids, in relation to their growth rate. Triglyceride levels were also assessed as a preferential source of biofuels.ResultsUsing statistical analysis, two centric diatoms, Thalassiosira weissflogii and Cyclotella cryptica, were selected as good candidates for oil production. Lipid levels significantly increased when the two diatoms were cultivated in a two-stage process under nitrogen limitation. The effect was less pronounced in cultures where silicon was reduced to 20% of the standard supply. Nitrogen limitation did not affect growth rates but led to lipid remodeling and de novo synthesis of triacylglycerols.ConclusionsTriacylglycerols in T. weissflogii and C. cryptica can account for up to 82% and 88% of total glycerolipids, thereby suggesting that the two species are promising candidates for large-scale experimentation for biofuel production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0212-4) contains supplementary material, which is available to authorized users.

Summary In recent years, oxylipins (lipoxygenase‐derived oxygenated fatty acid products) have been reported in several bloom‐forming marine diatoms. Despite increasing attention on the ecophysiological role of these molecules in marine environments, their biosynthesis is largely unknown in these microalgae. Biochemical methods, including tandem mass spectrometry, nuclear magnetic resonance and radioactive probes were used to identify structures, enzymatic activities and growth‐dependent modulation of oxylipin biosynthesis in the pennate diatom Pseudo‐nitzschia delicatissima. Three major compounds, 15S‐hydroxy‐(5Z,8Z,11Z,13E,17Z)‐eicosapentaenoic acid (15S‐HEPE), 15‐oxo‐5Z,9E,11E,13E‐pentadecatetraenoic acid and 13,14‐threo‐13R‐hydroxy‐14S,15S‐trans‐epoxyeicosa‐5Z,8Z,11Z,17Z‐tetraenoic acid (13,14‐HEpETE), were produced by three putative biochemical pathways triggered by eicosapentaenoic acid‐dependent 15S lipoxygenase. Oxylipin production increases along the growth curve, with remarkable changes that precede the demise of the culture. At least one of the compounds, namely 15‐oxoacid, is formed only in the stationary phase immediately before the collapse of the culture. Synthesis and regulation of phyco‐oxylipins seem to correspond to a signaling mechanism that governs adaptation of diatoms along the growth curve until bloom termination. Factors triggering the process are unknown but synthesis of 15‐oxoacid, constrained within a time‐window of a few days just before the collapse of the culture, implies the involvement of a physiological control not directly dependent on distress or death of diatom cells.