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In contrast to vascular plants, green algae, and diatoms, the major light-harvesting complex of the marine eustigmatophyte genus Nannochloropsis is a violaxanthin-chlorophyll a protein complex that lacks chlorophylls b and c. The isolation of a single polypeptide from the light-harvesting complex of Nannochloropsis sp. (IOLR strain) was previously reported (Sukenik et al. 1992). The NH2 -terminal amino acid sequence of this polypeptide was significantly similar to NH2 -terminal sequences of the light-harvesting fucoxanthin, chlorophyll a/c polypeptides from the diatom Phaeodactylum tricornutum Bohlin. Using polyclonal antibodies raised to the Nannochloropsis light-harvesting polypeptide, a gene encoding this polypeptide was isolated from a cDNA expression library. The deduced amino acid sequence of the Nannochloropsis violaxanthin-chlorophyll a polypeptide reveals a 36 amino acid presequence followed by 173 amino acids that constitute the mature polypeptide. The mature polypeptide has 30%-40% sequence identity to the diatom fucoxanthin-chlorophyll a/c polypeptides and less then 27% identity to the green algal and vascular plant light-harvesting chlorophyll polypeptides that bind both chlorophylls a and b. Its molecular mass, as deduced from the gene sequence, is 18.4 kDa with three putative transmembrane helices and several residues that may be involved in chlorophyll binding. The cDNA encoding the violaxanthin-chlorophyll a polypeptide was used to isolate and characterize a 10 kb genomic fragment containing the entire gene. The open reading frame was interrupted by five introns ranging in size from 123 to 449 bp. The intron borders have typical eukaryotic GT … AG sequences.

Filaments of Streblonema sp. isolated from hyperplasia (galls) on Nereocystis luetkeana (Mert.) Post. et Rupr. induced similar gall growths when inoculated on young sporophytes of Nereocystis luetkeana, Macrocystis integrifolia Bory, and Laminaria japonica Aresch. Filaments were irregularly branched and uniseriate with cells 5–8 μm in diameter and 10–30 μm long. Growth under varied cultured conditions produced unilocular sporangia. Zoospores released from the sporangia germinated into identical filaments which also formed unilocular sporangia. Gall tissue originated from the innermost cells of the epidermal meristematic zone. When infected these cells divided in an irregular and unorganized manner. The resulting structure was a pronounced departure from normal morphology.

Diatoms are unicellular brown algae that likely arose from the endocytobiosis of a red alga into a single-celled heterotroph and that constitute an algal class of major importance in phytoplankton communities around the globe. The first whole-genome sequence from a diatom species, Thalassiosira pseudonana Hasle et Heimdal, was recently reported, and features that are central to diatom physiology and ecology, such as silicon and nitrogen metabolism, iron uptake, and carbon concentration mechanisms, were described. Following this initial study, the basic cellular systems controlling cell signaling, gene expression, cytoskeletal structures, and response to stress have been cataloged in an attempt to obtain a global view of the molecular foundations that sustain such an ecologically successful group of organisms. Comparative analysis with several microbial, plant, and metazoan complete genome sequences allowed the identification of putative membrane receptors, signaling proteins, and other components of central interest to diatom ecophysiology and evolution. Thalassiosira pseudonana likely perceives light through a novel phytochrome and several cryptochrome photoreceptors; it may lack the conserved RHO small-GTPase subfamily of cell-polarity regulators, despite undergoing polarized cell-wall synthesis; and it possesses an unusually large number of heat-shock transcription factors, which may indicate the central importance of transcriptional responses to environmental stress. The availability of the complete gene repertoire will permit a detailed biochemical and genetic analysis of how diatoms prosper in aquatic environments and will contribute to the understanding of eukaryotic evolution.

A general purpose transformation vector, designated pPha-T1, was constructed for use with the diatom Phaeodactylum tricornutum Bohlin. This vector harbors the sh ble cassette for primary selection on medium containing the antibiotic zeocin, and a multiple cloning site flanked by the P. tricornutum fcpA promoter. pPha-T1 was used to establish the utility of three selectable marker genes and two reporter genes for P. tricornutum transformation. The nat and sat-1 genes confer resistance to the antibiotic nourseothricin, and nptII confers resistance to G418. Each of these genes was effective as a selectable marker for identifying primary transformants. These markers could also be used for dual selections in combination with the sh ble gene. The reporter genes uidA and gfp were also introduced into P. tricornutum using pPha-T1. Gus expression in some transformants reached 15 μg·μg−1 of total soluble protein and permitted excellent cell staining, while GFP fluorescence was readily visible with standard fluorescence microscopy. The egfp gene, which has optimal codon usage for expression in human cells, was the only version of gfp that produced a strong fluorescent signal in P. tricornutum. The codon bias of the egfp gene is similar to that of P. tricornutum genes. This study suggests that codon usage has a significant effect on the efficient expression of reporter genes in P. tricornutum. The results presented here demonstrate that a variety of selectable markers and reporter genes can be expressed in P. tricornutum, enhancing the potential of this organism for exploring basic biological questions and industrial applications.

Aglaothamnion neglectum Feldman-Mazoyer has two γ subunits, γ31 and γ33, that are associated with phycoerythrin in the light-harvesting phycobilisomes. We demonstrate that these subunits are spatially separated within the phycobilisome, with the γ31 subunit present at the distal end of phycobilisome rods and the γ33 subunit present on the proximal end. These subunits are thought to link phycoerythrin hexamers together in the rod substructure, serving a role analogous to that of linker polypeptides of cyanobacteria (although unlike the cyanobacterial linker polypeptides they are chromophorylated). The sequencing of tryptic polypeptides of the γ subunits enabled us to prepare oligonucleotides encoding different regions of γ31. These oligonucleotides were used as primers to generate a probe for isolating a γ31 cDNA clone. Characterization of the cDNA clone predicts a polypeptide of 280 amino acids with a 42 amino acid presequence that is characteristic of a transit peptide, the peptide that targets proteins to chloroplasts of vascular plants. The γ31 subunit has 50% similarity to the previously characterized γ33 subunit but has no identifiable similarity to functionally related polypeptides present in cyanobacterial phycobilisomes or to any other polypeptides in the databases. A repeat of 95 amino acids is present in the red algal γ subunit sequences, suggesting that these proteins were generated by a gene duplication followed by fusion of the duplicate sequences.

A number of important advances have occurred in microalgal biotechnology in recent years that are slowly moving the field into new areas. New products are being developed for use in the mass commercial markets as opposed to the “health food” markets. These include algal-derived long-chained polyunsaturated fatty acids, mainly docosahexaenoic acid, for use as supplements in human nutrition and animals. Large-scale production of algal fatty acids is possible through the use of heterotrophic algae and the adaptation of classical fermentation systems providing consistent biomass under highly controlled conditions that result in a very high quality product. New products have also been developed for use in the development of pharmaceutical and research products. These include stable-isotope biochemicals produced by algae in closed-system photobioreactors and extremely bright fluorescent pigments. Cryopreservation has also had a tremendous impact on the ability of strains to be maintained for long periods of time at low cost and maintenance while preserving genetic stability.

A strain of Gracilaria epihippisora Hoyle produces gall-like cell proliferations in culture. These growths can be excised and grown separately, where they retain an undifferentiated morphology and reach 5mm in diameter. The gall tissue consists of a single morphological cell type without any differentiation between surface and internal cells as is characteristic of normal thallus tissue. Gall cells are typically 20–40 μm in diameter and contain the usual complement of organelles and a prominent vacuole, although there are several distinct features. The large multilobed plastids have an extensive proliferation of thylakoid membranes, which form an arrangement of loops and spirals. The thallus outer cell wall layer is highly reduced. The gall growths contain intracellular virus-like particles (ca. 80 nm in diameter) that occur in discrete groups.

The gene encoding the β 18 subunit of allophycocyanin (apcF) is on the plastid genome of the red alga Aglaothamnion neglectum Feldman-Mazoyer. Immediately 3' of apcF and on the same transcript is a second open reading frame (ORF100) with homology (49% amino acid identity) to a gene tentatively identified as apcC in Cyanidium caldarium Geitler. The predicted amino acid sequence of the apcF gene product is 36% identical to analogous polypeptides from cyanobacteria. The apcF and ORF100 genes are clustered with other genes encoding phycobilisome polypeptides, which include the genes for the rod-core linker polypeptide and the α and β subunits of phycoerythrin

Diatoms and related algae have plastids that are surrounded by four membranes. The outer two membranes are continuous with the endoplasmic reticulum and the inner two membranes are analogous to the plastid envelope membranes of higher plants and green algae. Thus the plastids are completely compartmentalized within the ER membranes. The targeting presequences for nuclear-encoded plastid proteins have two recognizable domains. The first domain is a classic signal sequence, which presumably targets the proteins to the endoplasmic reticulum. The second domain has characteristics of a transit peptide, which targets proteins to the plastids of higher plants. To characterize these targeting domains, the presequence from the nuclear-encoded plastid protein AtpC was utilized. A series of deletions of this presequence were fused to Green Fluorescent Protein (GFP) and transformed into cells of the diatom, Phaeodactylum tricornutum. The intracelluar localization of GFP was visualized by fluorescence microscopy. This work demonstrates that the first domain of the presequence is responsible for targeting proteins to the ER lumen and is the essential first step in the plastid protein import process. The second domain is responsible to directing proteins from the ER and through the plastid envelope and only a short portion of the transit peptide-like domain is necessary to complete this second processing step. In vivo data generated from this study in a fully homologous transformation system has confirmed Gibbs' hypothesis regarding a multistep import process for plastid proteins in chromophytic algae.

The presence of the “symbiotic” red alga Hypneocolax stellaris Borgesen was found to substantially reduce the growth rate of Hypnea musciformis (Wulfen) Lamouroux. The growth rate of injected field material was 40% less than unifected thalli. Likewise, the growth rate of host thalli infected in the laboratory was reduced 70% compared to uninfected thalli. Neither the quantity nor quality of carrageenan extracted from Hypnea musciformis was directly affected by the presence of Hypneocolax stellaris. In a mariculture system the presence of a symbiotic alga on its host would be expected to reduce the host's growth rate and thereby lower its economic potential.