Based on morphological variation found in specimens ascribed to Pseudo‐nitzschia pseudodelicatissima and uncertainty regarding the delineation of P. pseudodelicatissima and P. cuspidata, cultures and field material of diatoms in the P. pseudodelicatissima/cuspidata complex were studied in morphological detail. Four different species were identified. The descriptions of the species P. pseudodelicatissima and P. cuspidata were emended on the basis of studies of type material. In addition, P. calliantha sp. nov. and P. caciantha sp. nov. were described as new species based on morphological and molecular data. The morphological differences among the species were found in characters such as width and shape of the valve, density of fibulae and striae, structural pattern of the poroid hymen, and structure of the girdle bands. The morphological studies were supported by phylogenetic analyses of the nuclear‐encoded internal transcribed spacer 1, 5.8S, and internal transcribed spacer 2 rDNA of 24 strains representing 16 different Pseudo‐nitzschia species. The description of the four species helps to explain the variation observed in mating experiments on cultures originally designated as P. pseudodelicatissima. At least two previous reports of toxin production in species identified as P. pseudodelicatissima have been identified as being caused by P. calliantha, and one additional report of toxin production has been identified as either P. pseudodelicatissima or P. cuspidata.

A study of 25 cultures tentatively identified as Pseudo-nitzschia delicatissima (Cleve) Heiden, and originating from geographically widely distributed locations, showed both morphological and genetic variation among strains. Use of rRNA-targeted DNA probes on 17 different strains showed large variation in the hybridization patterns. Detailed morphological studies placed the isolates into three groups. The sample on which the neotype of P. delicatissima is based was also examined, and used to establish the morphological identity of P. delicatissima. Phylogenetic analyses of 16 strains, based on sequences of internal transcriber spacer 1 (ITS1), 5.8S and ITS2 of the nuclear-encoded rDNA, supported the morphological observations and the hybridization studies, and revealed large genetic variation among strains. A combination of the morphological and molecular findings resulted in the description of two new species, P. decipiens sp. nov. and P. dolorosa sp. nov. P. dolorosa has a mixture of one or two rows of poroids in the striae whereas P. delicatissima always has two rows. In addition, P. dolorosa has wider valves and a lower density of poroids. P. decipiens differs from P. delicatissima by a higher density of striae on the valve face as well as a higher density of poroids on the girdle bands. Among the strains referred to P. delicatissima, an epitype was selected. Large genetic variation was found among the P. delicatissima strains and a subdivision into two major clades represent cryptic species.

Observation of coherent oscillations in the 2D electronic spectra (2D ES) of photosynthetic proteins has led researchers to ask whether nontrivial quantum phenomena are biologically significant. Coherent oscillations have been reported for the soluble light-harvesting phycobiliprotein (PBP) antenna isolated from cryptophyte algae. To probe the link between spectral properties and protein structure, we determined crystal structures of three PBP light-harvesting complexes isolated from different species. Each PBP is a dimer of αβ subunits in which the structure of the αβ monomer is conserved. However, we discovered two dramatically distinct quaternary conformations, one of which is specific to the genus Hemiselmis. Because of steric effects emerging from the insertion of a single amino acid, the two αβ monomers are rotated by ∼73°to an "open" configuration in contrast to the "closed" configuration of other cryptophyte PBPs. This structural change is significant for the light-harvesting function because it disrupts the strong excitonic coupling between two central chromophores in the closed form. The 2D ES show marked cross-peak oscillations assigned to electronic and vibrational coherences in the closedform PC645. However, such features appear to be reduced, or perhaps absent, in the open structures. Thus cryptophytes have evolved a structural switch controlled by an amino acid insertion to modulate excitonic interactions and therefore the mechanisms used for light harvesting.X-ray crystallography | quantum coherence | protein evolution | excitonic switching L ight-harvesting complexes capture and funnel the energy from light using organic chromophore molecules that are bound to scaffolding proteins. The protein structure thereby sets the relative positions and orientations of the chromophores to control excitation transport. In other words, the protein plays a deciding role in building the "electronic Hamiltonian"-the electronic coupling between chromophores and the chromophoric energy landscape that directs energy flow. This strong connection between structural biology and physics means that ultrafast light-harvesting functions are under genetic and evolutionary control. Cryptophytes, a group of marine and freshwater single-celled algae, are an intriguing example, because one of their light-harvesting antenna complexes was completely reengineered by combining a unique bilin-binding polypeptide with a single subunit from the ancestral red algal phycobilisome (1, 2). Here we report a further example of biological manipulation of this phycobiliprotein (PBP) light-harvesting system. We have discovered an elegant but powerful genetic switch that converts the common form of this PBP into a distinct structural form in which the mechanism underpinning light harvesting is vastly different-in essence because strong excitonic interactions within the PBP are switched from on to off.The crystal structure of the cryptophyte PBP phycoerythrin PE545 from Rhodomonas CS24 showed that the protein is a dimer of two αβ monomers (3, ...

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The plastid-bearing members of the Cryptophyta contain two functional eukaryotic genomes of different phylogenetic origin, residing in the nucleus and in the nucleomorph, respectively. These widespread and diverse protists thus offer a unique opportunity to study the coevolution of two different eukaryotic genomes within one group of organisms. In this study, the SSU rRNA genes of both genomes were PCR-amplified with specific primers and phylogenetic analyses were performed on different data sets using different evolutionary models. The results show that the composition of the principal clades obtained from the phylogenetic analyses of both genes was largely congruent, but striking differences in evolutionary rates were observed. These affected the topologies of the nuclear and nucleomorph phylogenies differently, resulting in long-branch attraction artifacts when simple evolutionary models were applied. Deletion of long-branch taxa stabilized the internal branching order in both phylogenies and resulted in a completely resolved topology in the nucleomorph phylogeny. A comparison of the tree topologies derived from SSU rDNA sequences with characters previously used in cryptophyte systematics revealed that the biliprotein type was congruent, but the type of inner periplast component incongruent, with the molecular trees. The latter is indicative of a hidden cellular dimorphism (cells with two periplast types present in a single clonal strain) of presumably widespread occurrence throughout cryptophyte diversity, which, in consequence, has far-reaching implications for cryptophyte systematics as it is practiced today.