Field testing for toxic algae with a microarray: initial results from the MIDTAL project

One of the key tasks in MIDTAL (MIcroarrays for the Detection of Toxic ALgae) is to demonstrate the applicability of microarrays to monitor harmful algae across a broad range of ecological niches and toxic species responsible for harmful algal events. Water samples are collected from a series of sites used in national phytoplankton and biotoxin monitoring across Europe. The samples are filtered; rRNA is extracted, labelled with a fluorescent dye and applied to a microarray chip. The signal intensity from >120 probes previously spotted on the chip is measured and analysed. Preliminary results comparing microarray signal intensities with actual field counts are presented.Versión del edito

Krill Excretion Boosts Microbial Activity in the Southern Ocean

Antarctic krill are known to release large amounts of inorganic and organic nutrients to the water column. Here we test the role of krill excretion of dissolved products in stimulating heterotrophic bacteria on the basis of three experiments where ammonium and organic excretory products released by krill were added to bacterial assemblages, free of grazers. Our results demonstrate that the addition of krill excretion products (but not of ammonium alone), at levels expected in krill swarms, greatly stimulates bacteria resulting in an order-of-magnitude increase in growth and production. Furthermore, they suggest that bacterial growth rate in the Southern Ocean is suppressed well below their potential by resource limitation. Enhanced bacterial activity in the presence of krill, which are major sources of DOC in the Southern Ocean, would further increase recycling processes associated with krill activity, resulting in highly efficient krill-bacterial recycling that should be conducive to stimulating periods of high primary productivity in the Southern Ocean.This research is a contribution to projects ICEPOS (REN2002-04165-CO3-O2) and ATOS (POL2006-00550/CTM), funded by the Spanish Ministry of Science and Innovation

Searching for DNA Lesions: Structural Evidence for Lower- and Higher-Affinity DNA Binding Conformations of Human Alkyladenine DNA Glycosylase

To efficiently repair DNA, human alkyladenine DNA glycosylase (AAG) must search the million-fold excess of unmodified DNA bases to find a handful of DNA lesions. Such a search can be facilitated by the ability of glycosylases, like AAG, to interact with DNA using two affinities: a lower-affinity interaction in a searching process and a higher-affinity interaction for catalytic repair. Here, we present crystal structures of AAG trapped in two DNA-bound states. The lower-affinity depiction allows us to investigate, for the first time, the conformation of this protein in the absence of a tightly bound DNA adduct. We find that active site residues of AAG involved in binding lesion bases are in a disordered state. Furthermore, two loops that contribute significantly to the positive electrostatic surface of AAG are disordered. Additionally, a higher-affinity state of AAG captured here provides a fortuitous snapshot of how this enzyme interacts with a DNA adduct that resembles a one-base loop.National Institutes of Health (U.S.) (grant no. P30-ES002109)National Institutes of Health (U.S.) (grant no. GM65337)National Institutes of Health (U.S.) (grant no. GM65337-03S2)National Institutes of Health (U.S.) (grant no. CA055042)National Institutes of Health (U.S.) (grant no. CA092584)Repligen Corporation (KIICR Graduate Fellowship

Minimising losses to predation during microalgae cultivation

We explore approaches to minimise impacts of zooplanktonic pests upon commercial microalgal crops using system dynamics models to describe algal growth controlled by light and nutrient availability and zooplankton growth controlled by crop abundance and nutritional quality. Losses of microalgal crops are minimised when their growth is fastest and, in contrast, also when growing slowly under conditions of nutrient exhaustion. In many culture systems, however, dwindling light availability due to self-shading in dense suspensions favours slow growth under nutrient sufficiency. Such a situation improves microalgal quality as prey, enhancing zooplankton growth, and leads to rapid crop collapse. Timing of pest entry is important; crop losses are least likely in established, nutrient-exhausted microalgal communities grown for high C-content (e.g. for biofuels). A potentially useful approach is to promote a low level of P-stress that does not adversely affect microalgal growth but which produces a crop that is suboptimal for zooplankton growth

The role of interactions between Prorocentrum minimum and Heterosigma akashiwo in bloom formation

We examined the growth and interactions between the bloom-forming flagellates Prorocentrum minimum and Heterosigma akashiwo using bi-algal culture experiments. When both species were inoculated at high cell densities, growth of H. akashiwo was inhibited by P. minimum. In other combinations of inoculation densities, the species first reaching the stationary phase substantially suppressed maximum cell densities of the other species, but the growth inhibition effect of P. minimum was stronger than that of H. akashiwo. We used a mathematical model to simulate growth and interactions of P. minimum and H. akashiwo in bi-algal cultures. The model indicated that P. minimum always out-competed H. akashiwo over time. Additional experiments showed that crude extracts from P. minimum and H. akashiwo cultures did not affect the growth of either species, but both strongly inhibited the growth of the bloom-forming diatom Skeletonema costatum. Further experiments showed that it was unlikely that reactive oxygen species produced by H. akashiwo were responsible for the inhibition of P. minimum growth