The active transport of Mg++ and Mn++ into the yeast cell

Certain bivalent cations, particularly Mg⁺⁺ and Mn⁺⁺, can be absorbed by yeast cells, provided that glucose is available, and that phosphate is also absorbed. The cation absorption is stimulated by potassium in low concentrations, but inhibited by higher concentrations. From the time course studies, it is apparent that the absorption rather than the presence of phosphate and the potassium is the important factor. Competition studies with pairs of cations indicate that binding on the surface of the cell is not a prerequisite to absorption. The absorption mechanism if highly selective for Mg⁺⁺ and Mn⁺⁺, as compared to Ca⁺⁺, Sr⁺⁺, and UO₂⁺⁺, whereas the binding affinity is greatest for UO₂⁺⁺, with little discrimination between Mg⁺⁺, Ca⁺⁺, Mn⁺⁺, and Sr⁺⁺. In contrast to the surface-bound cations which are completely exchangeable, the absorbed cations are not exchangeable. It is concluded that Mg⁺⁺ and Mn⁺⁺ are actively transported into the cell by a mechanism involving a phosphate and a protein constituent.     

Studies on the nutrition of Arthrobotrys oligospora Fres. and A. robusta Dudd: The predaceous phase

The effects of substrate on the predaceous activity in sand cultures of two isolates of the genus Arthrobotrys were measured by expressing the number of non-survivors of a free-living nematode population exposed to the fungi for 4 days as a percentage of a comparable population of nematodes not exposed to predation. This percentage is designated the predacity number. By varying the energy source it was shown that nutrient requirements for the extension of mycelium may differ from those for the expression of predacity. There is a greater reduction in the activity of A. oligospora when nitrogen is supplied as ammonium than when it is presented as nitrate or nitrite. The predacity of A. robusta is greatest on media deficient in biotin and with nitrite as nitrogen source. The relationship of results derived from artificial cultures to results from more direct examination of soils is discussed.     

Morphological and habitat evolution in the Cyanobacteria using a compartmentalization approach

A phylogenomic approach was used to study the evolution of traits in the Cyanobacteria. A cyanobacterial backbone tree was constructed using multiple concatenated sequences from whole genome sequences. Additional taxa were added using a separate alignment that contained morphological characters, SSU (small subunit) and LSU (large subunit) rDNA, rpoC, rpoD, tufA, and gyrB genes. A compartmentalization approach was then used to construct a robust phylogeny with resolved deep branches. Additional morphological characters (e.g. unicellular or filamentous growth, presence or absence of heterocysts) were coded, mapped onto the backbone cyanobacterial tree, and the ancestral character states inferred. Our analyses show that the earliest cyanobacterial lineages were likely unicellular coccoid/ellipsoidal/short rods that lived in terrestrial/freshwater environments. Later cyanobacterial lineages independently gained the ability to colonize brackish, marine, and hypersaline environments while acquiring a large number of more complex traits: sheath, filamentous growth, nitrogen fixation, thermophily, motility, and use of sulphide as an electron donor. Many of these adaptations would have been important in the appearance of dense microbial mats early in Earth's history. Complex traits such as hormogonia, heterocysts, and akinetes had a single ancestor. Within the Nostocales, hormogonia and heterocysts arose before akinetes.     

Six new microsatellite markers for the toxic marine dinoflagellate Alexandrium tamarense

We report the characterization of six new microsatellite loci for the toxic marine dinoflagellate Alexandrium tamarense (North American ribotype), using 56 isolates from a range of locations. The numbers of alleles per locus ranged from five to nine and gene diversities ranged from 0.041 to 0.722. We tested primers for these six loci on other A. tamarense ribotypes and on other Alexandrium species; the results suggest that the primers are specific to A. tamarense isolates belonging to the North American ribotype.     

Individual Variation in Anti-predator Responses in the Three-spined Stickleback (Gasterosteus aculeatus L.)

Inter-population differences in stickleback anti-predator behaviour in responses to predation risks are now well established (HUNTINGFORD 1982; GILES & HUNTINGFORD 1984). This paper reanalyses this data in search of individual behavioural differences in the exploration of a novel environment and escape strategy shown by sticklebacks when stalked by a hunting pike (Esox lucius). 8 factors (accounting for 70% of the variance in the original data) emerge from the analysis and significant sex and population effects are described. Factors 1 and 2 correspond to predator investigation and the level of boldness shown towards pike. Factors 3, 4 and 5 separate the escape response into three distinct tactics adopted by sticklebacks when being stalked by the pike. These behaviour groupings are independent of the activity of the stickleback before the presence of the pike is detected. Factors 6, 7 and 8 were comprised of activities (use of open water, of weed beds and of the cover provided by the bottom of the tank) which load heavily for both the periods before and after the sticklebacks reacted to the predator. These groupings may represent different anti-predator tactics adopted by individual sticklebacks.     

Deoxyribonucleic Acid Base Composition of Flavobacteria and Related Gram Negative Yellow Pigmented Rods

DNA base composition analyses on 35 Gram negative yellow pigmented rods indicated two distinct groups. The larger contained 29 strains with G + C contents of between 30·8 and 39·5% and comprise 19 non-gliding, aflagellate strains and 10 gliding strains. The smaller, a heterogenous collection of six strains, had G + C contents in the 51·4–63% range.