The taxonomic group Prochlorales (Lewin 1977) Burger-Wiersma, Stal and Mur 1989 was established to accommodate a set of prokaryotic oxygenic phototrophs which, like plant, green algal and euglenoid chloroplasts, contain chlorophyll b instead of phycobiliproteins. Prochlorophytes were originally proposed (with concomitant scepticism) to be a monophyletic group sharing a common ancestry with these 'green' chloroplasts. Results from molecular sequence phylogenies, however, have suggested that Prochlorothrix hollandica is not on a lineage that leads to plastids. Our results from 16S ribosomal RNA sequence comparisons, which include new sequences from the marine picoplankter Prochlorococcus marinus and the Lissoclinum patella symbiont Prochloron sp., indicate that prochlorophytes are polyphyletic within the cyanobacterial radiation, and suggest that none of the known species is specifically related to chloroplasts. This implies that the three prochlorophytes and the green chloroplast ancestor acquired chlorophyll b and its associated structural proteins in convergent evolutionary events. We report further that the 16S rRNA gene sequence from Prochlorococcus is very similar to those of open ocean Synechococcus strains (marine cluster A), and to a family of 16S rRNA genes shotgun-cloned from plankton in the north Atlantic and Pacific Oceans.

Diverse microbial ecosystems underpin life in the sea. Among these microbes are many unicellular eukaryotes that span the diversity of the eukaryotic tree of life. However, genetic tractability has been limited to a few species, which do not represent eukaryotic diversity or environmentally relevant taxa. Here, we report on the development of genetic tools in a range of protists primarily from marine environments. We present evidence for foreign DNA delivery and expression in 13 species never before transformed and for advancement of tools for eight other species, as well as potential reasons for why transformation of yet another 17 species tested was not achieved. Our resource in genetic manipulation will provide insights into the ancestral eukaryotic lifeforms, general eukaryote cell biology, protein diversification and the evolution of cellular pathways.

We provide an analysis of the invasion and spread of the container inhabiting mosquitoes Aedes aegypti and Aedes albopictus in the Bermuda Islands. Considered eradicated in the mid-1960s, A. aegypti was redetected in 1997, and A. albopictus was first detected in 2000. Based on weekly ovitrap data collected during the early stages of the invasion, we mapped the spread of Aedes throughout the islands. We analyzed the effects of buildings and roads on mosquito density and found a significant association between density and distance to roads, but not to buildings. We discuss the potential role of human transport in the rapid spread in the islands. The temporal correlation in ovitrap collection values decreased progressively, suggesting that habitat degradation due to control efforts were responsible for local shifts in mosquito densities. We report a sharp decrease in A. aegypti presence and abundance after the arrival of A. albopictus in the year 2000. Possible mechanisms for this rapid decline at relatively low density of the second invader are discussed in the context of classical competition theory and earlier experimental results from Florida, as well as alternative explanations. We suggest that support for the competition hypothesis to account for the decline of A. aegypti is ambiguous and likely to be an incomplete explanation.

Deepened isotherms associated with El Niño resulted in severe nutrient limitation and very low kelp productivity during the last half of 1983. Frond growth rates were so low that terminal blades formed before reaching the surface, eliminating the canopy. Frond initiation rates were also extremely low, resulting in significant reductions in mean plant size. Plants growing above 10 m were more severely affected than plants at 20 m. These results suggest that nutrient pulses associated with internal waves are critical for survival of Macrocystis pyrifera in nutritionally marginal habitats in southern California.

Regulation of antioxidant enzymes is critical to control the levels of reactive oxygen species in cell compartments highly susceptible to oxidative stress. In this work, we studied the regulation of a chloroplastic iron superoxide dismutase (Fe-SOD) from Lingulodinium polyedrum (formerly Gonyaulax polyedra) under different physiological conditions. A cDNA-encoding Fe-SOD was isolated from this dinoflagellate, showing high sequence similarity to cyanobacterial, algal, and plant FeSODs. Under standard growth conditions, on a 12:12-h light-dark cycle, Lingulodinium polyedrum Fe-SOD exhibited a daily rhythm of activity and cellular abundance with the maximum occurring during the middle of the light phase. Northern analyses showed that this rhythmicity is not related to changes in Fe-SOD mRNA levels, indicative of translational regulation. By contrast, conditions of metal-induced oxidative stress resulted in higher levels of Fe-SOD transcripts, suggesting that transcriptional control is responsible for increased protein and activity levels. Daily (circadian) and metalinduced up-regulation of Fe-SOD expression in L. polyedrum are thus mediated by different regulatory pathways, allowing biochemically distinct changes appropriate to oxidative challenges. Reactive oxygen species (ROS)1 such as superoxide (O 2 . ), and in some cases hydrogen peroxide (H 2 O 2 ), are normal by-products of oxidative metabolism and have the potential to give rise to hydroxyl radicals (HO ⅐ ). Although some ROS may function as important signaling molecules that alter gene expression and modulate the activity of specific defense proteins (1), all ROS may be harmful and pose a threat to aerobic organisms. Oxidative damage to DNA, proteins, and lipids can lead to mutagenesis, carcinogenesis, and alterations in cell structure (2). Organisms combat toxic effects of oxygen with antioxidants, which include detoxifying enzymes and low molecular weight compounds. The enzyme superoxide dismutase (SOD) represents a first step in such ROS scavenging systems. SOD isoforms, including the copper/zinc-containing (CuZn-SOD), manganese-containing (Mn-SOD), and iron-containing (Fe-SOD) metalloenzymes, catalyze the dismutation of O 2. to H 2 O 2 and oxygen. In photosynthetic eukaryotes, CuZn-SOD is usually located in the cytosol and extracellular space, although some plants also possess a chloroplastic CuZn-SOD isoform. Mn-SOD and Fe-SOD are found within the mitochondria and chloroplast, respectively (3).Irradiation by visible light in the presence of a photosensitizer leads to the production of ROS, which in plants and algae is linked to photosynthesis (4). Because of the elevated oxygen concentration and intense electron flux within chloroplasts, electrons inevitably react with oxygen, thereby generating O 2 . , which dismutates to oxygen and H 2 O 2 , producing the highly reactive HO ⅐ through the metal ion catalyzed Haber-Weiss reaction (5). Even under nonstress conditions, this ROS-generating mechanism can do harm and inactivate the photosystem II reaction ...

Regulation and evolution of dinoflagellate luciferases are of particular interest since the enzyme is structurally unique and bioluminescence is under circadian control. In this study, three new members of the dinoflagellate luciferase gene family were identified and characterized from Pyrocystis lunula. These genes, lcfA, lcfB, and lcfC, also exhibit the unusual structure and organization previously reported for the luciferase gene of a related dinoflagellate, Lingulodinium polyedrum: three repeated domains, each encoding an active catalytic site, multiple gene copies, and tandem organization. The histidine residues involved in the pH regulation of L. polyedrum luciferase activity, and implicated in the regulation of flashing, are also fully conserved in P. lunula. The interspecific conservation between the individual luciferase domains of P. lunula and L. polyedrum is higher than among domains intramolecularly, indicating that this unique gene structure arose through duplication events that occurred prior to the divergence of these dinoflagellates. However, P. lunula luciferase genes differ from L. polyedrum in several respects, notably, the occurrence of an intron in one gene (lcfC), a 2.25-kb intergenic region connecting lcfA and lcfB, and, of particular interest, an invariant rate of synonymous (silent) substitutions along the repeat domains, in contrast to L. polyedrum luciferase, where the occurrence of synonymous substitutions is practically absent in the central region of the domains.

Multi‐locus DNA fingerprints using an M13 probe were obtained for eight individuals of giant kelp Macrocystis pyrifera (L.) C. Ag. collected from Monterey Bay, California. For each individual, DNA was extracted from a diploid blade and from ca. 109 haploid spores that were released from four to Jive sporophylls. Viable or swimming spores from one individual were pooled and referred to as a spore group. A total of 34 bands (4–19 kb) was detected in DNA fingerprints from the eight blades and eight spore groups, with individual blade or spore groups exhibiting 7–18 bands (mean = 12.6). One band (4.5 kb) was present in all 16 samples. Eight bands were detected in 11–14 of the 16 samples. Similarity indices were calculated for all pairwise comparisons of fingerprint bands among all possible combinations of blades and spore groups. Mean similarity indices for the eight blades (0.51, SE = 0.032) and spore groups (0.56, SE = 0.031) were significantly lower than for the eight comparisons of the blade and spore groups from a single individual (0.86, SE = 0.052). The data indicate that DNA fingerprints can be used to measure genetic variation within populations of M. pyrifera because variation of DNA fingerprints associated with meiotic products (spores) of a given individual is small relative to variation observed among individuals within the population. Additionally, fingerprint variation between diploid vegetative tissue and haploid meiotic products may be a measure of genetic change due to recombination or DNA turnover mechanisms.

BackgroundGlutamine synthetase (GS) is essential for ammonium assimilation and the biosynthesis of glutamine. The three GS gene families (GSI, GSII, and GSIII) are represented in both prokaryotic and eukaryotic organisms. In this study, we examined the evolutionary relationship of GSII from eubacterial and eukaryotic lineages and present robust phylogenetic evidence that GSII was transferred from γ-Proteobacteria (Eubacteria) to the Chloroplastida.ResultsGSII sequences were isolated from four species of green algae (Trebouxiophyceae), and additional green algal (Chlorophyceae and Prasinophytae) and streptophyte (Charales, Desmidiales, Bryophyta, Marchantiophyta, Lycopodiophyta and Tracheophyta) sequences were obtained from public databases. In Bayesian and maximum likelihood analyses, eubacterial (GSIIB) and eukaryotic (GSIIE) GSII sequences formed distinct clades. Both GSIIB and GSIIE were found in chlorophytes and early-diverging streptophytes. The GSIIB enzymes from these groups formed a well-supported sister clade with the γ-Proteobacteria, providing evidence that GSIIB in the Chloroplastida arose by horizontal gene transfer (HGT). Bayesian relaxed molecular clock analyses suggest that GSIIB and GSIIE coexisted for an extended period of time but it is unclear whether the proposed HGT happened prior to or after the divergence of the primary endosymbiotic lineages (the Archaeplastida). However, GSIIB genes have not been identified in glaucophytes or red algae, favoring the hypothesis that GSIIB was gained after the divergence of the primary endosymbiotic lineages. Duplicate copies of the GSIIB gene were present in Chlamydomonas reinhardtii, Volvox carteri f. nagariensis, and Physcomitrella patens. Both GSIIB proteins in C. reinhardtii and V. carteri f. nagariensis had N-terminal transit sequences, indicating they are targeted to the chloroplast or mitochondrion. In contrast, GSIIB proteins of P. patens lacked transit sequences, suggesting a cytosolic function. GSIIB sequences were absent in vascular plants where the duplication of GSIIE replaced the function of GSIIB.ConclusionsPhylogenetic evidence suggests GSIIB in Chloroplastida evolved by HGT, possibly after the divergence of the primary endosymbiotic lineages. Thus while multiple GS isoenzymes are common among members of the Chloroplastida, the isoenzymes may have evolved via different evolutionary processes. The acquisition of essential enzymes by HGT may provide rapid changes in biochemical capacity and therefore be favored by natural selection.