Prey preference in a kleptoplastic dinoflagellate is linked to photosynthetic performance.

Dinoflagellates of the family Kryptoperidiniaceae, known as "dinotoms", possess diatom-derived endosymbionts and contain individuals at three successive evolutionary stages: a transiently maintained kleptoplastic stage; a stage containing multiple permanently maintained diatom endosymbionts; and a further permanent stage containing a single diatom endosymbiont. Kleptoplastic dinotoms were discovered only recently, in Durinskia capensis; until now it has not been investigated kleptoplastic behavior and the metabolic and genetic integration of host and prey. Here, we show D. capensis is able to use various diatom species as kleptoplastids and exhibits different photosynthetic capacities depending on the diatom species. This is in contrast with the prey diatoms in their free-living stage, as there are no differences in their photosynthetic capacities. Complete photosynthesis including both the light reactions and the Calvin cycle remain active only when D. capensis feeds on its habitual associate, the "essential" diatom Nitzschia captiva. The organelles of another edible diatom, N. inconspicua, are preserved intact after ingestion by D. capensis and expresses the psbC gene of the photosynthetic light reaction, while RuBisCO gene expression is lost. Our results indicate that edible but non-essential, "supplemental" diatoms are used by D. capensis for producing ATP and NADPH, but not for carbon fixation. D. capensis has established a species-specifically designed metabolic system allowing carbon fixation to be performed only by its essential diatoms. The ability of D. capensis to ingest supplemental diatoms as kleptoplastids may be a flexible ecological strategy, to use these diatoms as "emergency supplies" while no essential diatoms are available.

Isolation from a fish kill and transcriptomic characterization of Gyrodinium jinhaense off Long Island Sound.

First found in Korean coastal water, the dinoflagellate Gyrodinium jinhaense is a recently established species with unclear global distribution and unexplored genomic characteristics. From a laboratory fish mortality event off Long Island Sound, USA, we isolated a dinoflagellate, and by microscopic and molecular (18S rRNA gene; >99% identical) analyses found that it resembles G. jinhaense, hence named G. jinhaense strain AP17. Towards developing a genetic database for this dinoflagellate, a transcriptome of this species was sequenced using RNA-seq, producing 6 Gbp of data that was assembled into over 70,000 unigenes. The assembled transcriptome GC content was approximately 56% and the total Benchmarking Universal Single-Copy Orthologs for Eukaryota and Alveolata databases were approximately 50% and 57%, respectfully. Genes involved in grazing, energy generation, genome architecture, and protein synthesis, processing, and degradation were highly represented in the transcriptome. Moreover, fragments of polyketide synthase and saxitoxin genes were found but saxitoxins were not detected in high performance liquid chromatography measurements. With the first reported transcriptome for the Gyrodinium genus, this study will serve as a baseline for future Gyrodinium genomics and toxicological studies.

Nuclear Gene Transformation in the Dinoflagellate Oxyrrhis marina.

The lack of a robust gene transformation tool that allows proper expression of foreign genes and functional testing for the vast number of nuclear genes in dinoflagellates has greatly hampered our understanding of the fundamental biology in this ecologically important and evolutionarily unique lineage of microeukaryotes. Here, we report the development of a dinoflagellate expression vector containing various DNA elements from phylogenetically separate dinoflagellate lineages, an electroporation protocol, and successful expression of introduced genes in an early branching dinoflagellate, Oxyrrhis marina. This protocol, involving the use of Lonza's Nucleofector and a codon-optimized antibiotic resistance gene, has been successfully used to produce consistent results in several independent experiments for O. marina. It is anticipated that this protocol will be adaptable for other dinoflagellates and will allow characterization of many novel dinoflagellate genes.

Insights into the red algae and eukaryotic evolution from the genome of Porphyra umbilicalis (Bangiophyceae, Rhodophyta).

Porphyra umbilicalis (laver) belongs to an ancient group of red algae (Bangiophyceae), is harvested for human food, and thrives in the harsh conditions of the upper intertidal zone. Here we present the 87.7-Mbp haploid Porphyra genome (65.8% G + C content, 13,125 gene loci) and elucidate traits that inform our understanding of the biology of red algae as one of the few multicellular eukaryotic lineages. Novel features of the Porphyra genome shared by other red algae relate to the cytoskeleton, calcium signaling, the cell cycle, and stress-tolerance mechanisms including photoprotection. Cytoskeletal motor proteins in Porphyra are restricted to a small set of kinesins that appear to be the only universal cytoskeletal motors within the red algae. Dynein motors are absent, and most red algae, including Porphyra, lack myosin. This surprisingly minimal cytoskeleton offers a potential explanation for why red algal cells and multicellular structures are more limited in size than in most multicellular lineages. Additional discoveries further relating to the stress tolerance of bangiophytes include ancestral enzymes for sulfation of the hydrophilic galactan-rich cell wall, evidence for mannan synthesis that originated before the divergence of green and red algae, and a high capacity for nutrient uptake. Our analyses provide a comprehensive understanding of the red algae, which are both commercially important and have played a major role in the evolution of other algal groups through secondary endosymbioses.

Respiratory membrane endo-hydrogenase activity in the microaerophile Azorhizobium caulinodans is bidirectional.

BACKGROUND: The microaerophilic bacterium Azorhizobium caulinodans, when fixing N(2) both in pure cultures held at 20 µM dissolved O(2) tension and as endosymbiont of Sesbania rostrata legume nodules, employs a novel, respiratory-membrane endo-hydrogenase to oxidize and recycle endogenous H(2) produced by soluble Mo-dinitrogenase activity at the expense of O(2). METHODS AND FINDINGS: From a bioinformatic analysis, this endo-hydrogenase is a core (6 subunit) version of (14 subunit) NADH:ubiquinone oxidoreductase (respiratory complex I). In pure A. caulinodans liquid cultures, when O(2) levels are lowered to <1 µM dissolved O(2) tension (true microaerobic physiology), in vivo endo-hydrogenase activity reverses and continuously evolves H(2) at high rates. In essence, H(+) ions then supplement scarce O(2) as respiratory-membrane electron acceptor. Paradoxically, from thermodynamic considerations, such hydrogenic respiratory-membrane electron transfer need largely uncouple oxidative phosphorylation, required for growth of non-phototrophic aerobic bacteria, A. caulinodans included. CONCLUSIONS: A. caulinodans in vivo endo-hydrogenase catalytic activity is bidirectional. To our knowledge, this study is the first demonstration of hydrogenic respiratory-membrane electron transfer among aerobic (non-fermentative) bacteria. When compared with O(2) tolerant hydrogenases in other organisms, A. caulinodans in vivo endo-hydrogenase mediated H(2) production rates (50,000 pmol 10(9)·cells(-1) min(-1)) are at least one-thousandfold higher. Conceivably, A. caulinodans respiratory-membrane hydrogenesis might initiate H(2) crossfeeding among spatially organized bacterial populations whose individual cells adopt distinct metabolic states in response to variant O(2) availability. Such organized, physiologically heterogeneous cell populations might benefit from augmented energy transduction and growth rates of the populations, considered as a whole.