Loss of nitrous oxide reductase in Pseudomonas aeruginosa cultured under N2O as determined by rocket immunoelectrophoresis

The mass ratio of nitrous oxide reductase to total protein in the soluble protein fraction of Pseudomonas aeruginosa P2 was highest in cells grown on nitrate, decreased in cells grown on N(2)O following the exhaustion of the initial charge of nitrate, and was nearly zero in cells exposed solely to N(2)O.     

Proton translocation during denitrification by a nitrifying-denitrifying Alcaligenes sp.

A heterotrophic nitrifying Alcaligenes sp. from soil was grown as a denitrifier on nitrate and subjected to oxidant pulse experiments to ascertain the apparent effeciencies of proton translocations during O₂ and nitrogen-oxide respirations. With endogenous substrate as the reducing agent the H⁺/2e^– ratios, extrapolated to zero amount of oxidant per pulse, were 9.4, 3.7, 4.3 and 3.5 for O₂, nitrate, nitrite and N₂O, respectively. The value for O₂ and those for the N-oxides are, respectively, somewhat larger and smaller than corresponding values for Paracoccus denitrificans. None of the three permeant ions employed with the Alcaligenes sp. (valinomycin-K⁺, thiocyanate and triphenylmethylphosphonium) was ideal for all purposes. Thiocyanate provided highest ratios for O₂ but abolished the oxidant pulse response for nitrate and N₂O. Valinomycin was slow to penetrate to the cytoplasmic membrane and relatively high concentrations were required for optimal performance. Triphenylmethylphosphonium enhanced passive proton permeability and diminished proton translocation at concentrations required to realize the maximal oxidant pulse response.     

Incipient Speciation by Sexual Isolation in Drosophila Melanogaster: Extensive Genetic Divergence without Reinforcement

The collection of Drosophila melanogaster from Zimbabwe and nearby regions (the Z-type) yield females who would not mate with the cosmopolitan D. melanogaster males (the M-type). To dissect the genetic basis of this sexual isolation, we constructed 16 whole-chromosome substitution lines between two standard Z-and M-lines. The results were as follows: (1) All substitution lines appear normal in viability and fertility in both sexes, indicating no strong postmating isolation. (2) The genes for the behaviors are mapped to all three major chromosomes with the same ranking and comparable magnitude of effects for both sexes: III > II >> X >/= 0 (III, II and X designate the effects of the three chromosomes). The results suggest less evolution on the X than on autosomes at loci of sexual behavior. (3) The genes for ``Z-maleness' are many and somewhat redundant. Whole-chromosome effects for Z-maleness appear nearly additive and show little dominance. (4) In contrast, ``Z-femaleness' has less redundancy as partial genotypes never exhibit full phenotypic effects. Epistatic interactions and incomplete dominance can sometimes be detected. (5) The extensive genetic divergence underlying sexual isolation has evolved in the absence of detectable reduction in hybrid fitnesses. Sexual selection has apparently been a driving force of multiple facets of speciation at the nascent stage without reinforcement.     

Partial purification and characterization of nitrous oxide reductase fromParacoccus denitrificans

We report the first partial purification of nitrous oxide reductase, a unique and labile enzyme of denitrifying bacteria. The procedure, which required anaerobic conditions throughout, resulted in a 60-fold purification relative to crude lysate in the case ofParococcus denitrificans. The molecular weight was estimated by gel exclusion chromatography to be about 85,000. The partially purified enzyme is inactivated rapidly by O₂, dithionite, and mercaptoethanol and is reversibly inhibited by moderate concentrations of common salts. Up to 80% of the original activity can be reconstituted following O₂ inactivation by incubating the enzyme with reduced benzyl viologen for 2 to 3 h. TheV _max pH profile shows a broad maximum at pH 8. The enzyme is irreversibly retained by common anion exchangers in the range pH 7 to 8 but can be eluted in acceptable yield as one of the last components from an imidazole-based anion exchange material by means of a pH gradient. This behavior implies that nitrous oxide reductase is very acidic. Among the several peptides observed by sodium dodecyl sulfate slab electrophoresis, only two, with apparent molecular weights of 58,000 and 25,000, correlated closely with the activity of fractions eluted from the imidazole column. These two peptides together comprised about 30% of the total protein in the fractions with highest specific activity.     

Reduction of nitrite to nitric oxide by enteric bacteria

Seven bacteria representing seven genera of enteric bacteria, in addition to Escherichia coli, were shown to reduce nitrite to NO under anaerobic conditions when the cells were grown as nitrate respirers. NO production was inhibited by nitrate and azide and was self limiting, just as was found to be the case previously with E. coli and its nitrate reductase. Maximum initial rates of NO production were observed at pH 5.5-6.     

Contrasting modes of natural selection acting on pigmentation genes in the Drosophila dunni subgroup

Genes that encode for divergent adaptive traits may have genealogies that contrast with those from loci that are not functionally involved in differentiation. Here, we examine DNA sequence variation among the species of the eastern Caribbean Drosophila dunni subgroup at two loci, yellow and dopa decaboxylase (Ddc), which both play integral roles in pigmentation patterning of adult Drosophila. Phylogenetic analyses of these loci produce gene genealogies with topologies that mirror those described for other nuclear genes: the six morphologically distinct species within the subgroup are divided into only three lineages, with one lineage containing four species that share extensive ancestral polymorphism. At the Ddc locus these major lineages are delineated only by silent site variation. We observe a significantly higher rate of synonymous site divergence than non-synonymous divergence, consistent with strong purifying selection acting on the locus. In contrast, the yellow locus exhibits patterns of amino acid divergence and nucleotide diversity that are consistent with recent diversifying selection acting in two different lineages. This selection appears to be targeting amino acid variants in the signal sequence of the Yellow protein, a region which is tightly constrained among members of the larger D. cardini radiation. This result highlights not only the potential importance of yellow in the evolution of divergent pigmentation patterns among members of the D. dunni subgroup, but also hints that variation in signal peptide sequences may play a role in phenotypic diversification.     

The anthropogenic environment lessens the intensity and prevalence of gastrointestinal parasites in Balinese long-tailed macaques (<Emphasis Type="Italic">Macaca fascicularis</Emphasis>)

The distribution of wildlife parasites in a landscape is intimately tied to the spatial distribution of hosts. In parasite species, including many gastrointestinal parasites, with obligate or common environmental life stages, the dynamics of the parasite can also be strongly affected by geophysical components of the environment. This is especially salient in host species, for example humans and macaques, which thrive across a wide variety of habitat types and quality and so are exposed to a wealth of environmentally resilient parasites. Here, we examine the effect of environmental and anthropogenic components of the landscape on the prevalence, intensity, and species diversity of gastrointestinal parasites across a metapopulation of long-tailed macaques on the island of Bali, Indonesia. Using principal-components analysis, we identified significant interaction effects between specific environmental and anthropogenic components of the landscape, parsing the Balinese landscape into anthropogenic (PC1), mixed environment (PC2), and non-anthropogenic (PC3) components. Further, we determined that the anthropogenic environment can mitigate the prevalence and intensity of specific gut parasites and the intensity of the overall community of gut parasites, but that non-anthropogenically driven landscape components have no significant effect in increasing or reducing the intensity or prevalence of the community of gut parasites in Balinese macaques.