Iron stress in open-ocean cyanobacteria (Synechococcus, Trichodesmium, and Crocosphaera spp.): identification of the IdiA protein.

Cyanobacteria are prominent constituents of the marine biosphere that account for a significant percentage of oceanic primary productivity. In an effort to resolve how open-ocean cyanobacteria persist in regions where the Fe concentration is thought to be limiting their productivity, we performed a number of Fe stress experiments on axenic cultures of marine Synechococcus spp., Crocosphaera sp., and Trichodesmium sp. Through this work, we determined that all of these marine cyanobacteria mount adaptive responses to Fe stress, which resulted in the induction and/or repression of several proteins. We have identified one of the Fe stress-induced proteins as an IdiA homologue. Genomic observations and laboratory data presented herein from open-ocean Synechococcus spp. are consistent with IdiA having a role in cellular Fe scavenging. Our data indicate that IdiA may make an excellent marker for Fe stress in open-ocean cyanobacterial field populations. By determining how these microorganisms respond to Fe stress, we will gain insight into how and when this important trace element can limit their growth in situ. This knowledge will greatly increase our understanding of how marine Fe cycling impacts oceanic processes, such as carbon and nitrogen fixation.     

“Wall-papering” and elaborate nest architecture in the ponerine antHarpegnathos saltator

Summary Excavation of 18 nests ofHarpegnathos saltator from southern India revealed an unusually complex architecture for a ponerine ant. The inhabited chambers are not deep in the ground. The uppermost chamber is protected by a thick vaulted roof, on the outside of which is an intervening space serving as isolation from the surrounding soil. In large colonies, the vaulted roof is extended into a shell which encloses several superimposed chambers. Little openings, which may be encircled by moulded flanges, occur in the upper region of the shell. The inside of the chambers is partly or completely lined with strips of empty cocoons. A refuse chamber is always found deeper than the inhabited chambers; live dipteran larvae (family Milichiidae) are typically present. These elaborate nests represent a large energetic investment, and we speculate therefore that nest emigration is unlikely in this species. Consequently, colony fission may never occur, unlike other ants where gamergates reproduce.     

Relationship between the transport from isolated nuclei of two abundant cytoplasmic messengers and the source of a messenger RNA transport factor

Messenger RNA transport from isolated nuclei requires a 35×10³ dalton cytoplasmic protein(s) which is present in both the cytosol and polyribosome fractions. Recombinant DNA probes containing cDNA inserts were used to quantitate the transport of rat liver-specific albumin and male rat liver-specific ₂U-globulin messenger RNA (mRNA) from male rat liver nuclei in response to the mRNA transport factors from homologous and heterologous tissues. No mRNA transport occurs in the absence of the transport factor(s). Both messengers are transported proportionately in response to the factor(s) from male or female rat liver cytosol, or from the polyribosomes (messenger ribonucleoprotein) of male or female rat liver, or brain. The transport factor(s) do not, therefore, appear to differentiate between the coding sequences of two unrelated hepatic messenger RNA's.     

Temperature Coefficients for the Oxidative Metabolic Responses to Electrical Stimulation in Cerebral Cortex

Temperature coefficients of both cat and toad brain have been calculated for the active metabolic state induced by electrical stimulation. Values are higher than most of the values previously reported for "rest" metabolism, whether calculated from Arrhenius plots or from linear graphs. Relative rates of oxidative metabolism were obtained by measuring the time course of the transient changes in NADH fluorescence and cytochrome aa3 absorption by reflectance techniques directly from the surface of the exposed cat cerebral cortex in vivo and from the isolated intact toad brain mounted in a cuvet. These findings demonstrate that such optical methods accurately record metabolic processes.     

Identification of DSB-1, a Protein Required for Initiation of Meiotic Recombination in Caenorhabditis elegans,Illuminates a Crossover Assurance Checkpoint

Meiotic recombination, an essential aspect of sexual reproduction, is initiated by programmed DNA double-strand breaks (DSBs). DSBs are catalyzed by the widely-conserved Spo11 enzyme; however, the activity of Spo11 is regulated by additional factors that are poorly conserved through evolution. To expand our understanding of meiotic regulation, we have characterized a novel gene, dsb-1, that is specifically required for meiotic DSB formation in the nematode Caenorhabditis elegans. DSB-1 localizes to chromosomes during early meiotic prophase, coincident with the timing of DSB formation. DSB-1 also promotes normal protein levels and chromosome localization of DSB-2, a paralogous protein that plays a related role in initiating recombination. Mutations that disrupt crossover formation result in prolonged DSB-1 association with chromosomes, suggesting that nuclei may remain in a DSB-permissive state. Extended DSB-1 localization is seen even in mutants with defects in early recombination steps, including spo-11, suggesting that the absence of crossover precursors triggers the extension. Strikingly, failure to form a crossover precursor on a single chromosome pair is sufficient to extend the localization of DSB-1 on all chromosomes in the same nucleus. Based on these observations we propose a model for crossover assurance that acts through DSB-1 to maintain a DSB-permissive state until all chromosome pairs acquire crossover precursors. This work identifies a novel component of the DSB machinery in C. elegans, and sheds light on an important pathway that regulates DSB formation for crossover assurance.     

Science Educational Outreach Programs That Benefit Students and Scientists

Both scientists and the public would benefit from improved communication of basic scientific research and from integrating scientists into education outreach, but opportunities to support these efforts are limited. We have developed two low-cost programs—"Present Your PhD Thesis to a 12-Year-Old" and "Shadow a Scientist”—that combine training in science communication with outreach to area middle schools. We assessed the outcomes of these programs and found a 2-fold benefit: scientists improve their communication skills by explaining basic science research to a general audience, and students'' enthusiasm for science and their scientific knowledge are increased. Here we present details about both programs, along with our assessment of them, and discuss the feasibility of exporting these programs to other universities.     

Malaria in Africa: vector species' niche models and relative risk maps

A central theoretical goal of epidemiology is the construction of spatial models of disease prevalence and risk, including maps for the potential spread of infectious disease. We provide three continent-wide maps representing the relative risk of malaria in Africa based on ecological niche models of vector species and risk analysis at a spatial resolution of 1 arc-minute (9 185 275 cells of approximately 4 sq km). Using a maximum entropy method we construct niche models for 10 malaria vector species based on species occurrence records since 1980, 19 climatic variables, altitude, and land cover data (in 14 classes). For seven vectors (Anopheles coustani, A. funestus, A. melas, A. merus, A. moucheti, A. nili, and A. paludis) these are the first published niche models. We predict that Central Africa has poor habitat for both A. arabiensis and A. gambiae, and that A. quadriannulatus and A. arabiensis have restricted habitats in Southern Africa as claimed by field experts in criticism of previous models. The results of the niche models are incorporated into three relative risk models which assume different ecological interactions between vector species. The "additive" model assumes no interaction; the "minimax" model assumes maximum relative risk due to any vector in a cell; and the "competitive exclusion" model assumes the relative risk that arises from the most suitable vector for a cell. All models include variable anthrophilicity of vectors and spatial variation in human population density. Relative risk maps are produced from these models. All models predict that human population density is the critical factor determining malaria risk. Our method of constructing relative risk maps is equally general. We discuss the limits of the relative risk maps reported here, and the additional data that are required for their improvement. The protocol developed here can be used for any other vector-borne disease.