Nitric oxide reduction in BioDeNOx reactors: kinetics and mechanism

Biological reduction of nitric oxide (NO) to di-nitrogen (N(2)) gas in aqueous Fe(II)EDTA(2-) solutions is a key reaction in BioDeNOx, a novel process for NOx removal from flue gases. The mechanism and kinetics of the first step of NO reduction, that is, the conversion of NO to N(2)O, was determined in batch experiments using various types of inocula. Experiments were performed in Fe(II)EDTA(2-) medium (5-25 mM) under BioDeNOx reactor conditions (55 degrees C, pH 7.2 +/- 0.2) with ethanol as external electron donor. BioDeNOx reactor mixed liquor gave the highest NO reduction rates (+/-0.34 nmol s(-1) mg(prot)(-1)) with an estimated K(m) value for NO lower than 10 nM. The specific NO (to N(2)O) reduction rate depended on the NO (aq) and Fe(II)EDTA(2-) concentration as well as the temperature. The experimental results, complemented with kinetic and thermodynamic considerations, show that Fe(II)EDTA(2-), and not ethanol, is the primary electron donor for NO reduction, that is, the BioDeNOx reactor medium (the redox system Fe(II)EDTA(2-)/Fe(III)EDTA(-)) interferes with the NO reduction electron transfer chain and thus enhances the NO denitrification rate.     

A CUG codon adapted two-hybrid system for the pathogenic fungus Candida albicans

The genetics of the most common human pathogenic fungus Candida albicans has several unique characteristics. Most notably, C. albicans does not follow the universal genetic code, by translating the CUG codon into serine instead of leucine. Consequently, the use of Saccharomyces cerevisiae as a host for yeast two-hybrid experiments with C. albicans proteins is limited due to erroneous translation caused by the aberrant codon usage of C. albicans. To circumvent the need for heterologous expression and codon optimalization of C. albicans genes we constructed a two-hybrid system with C. albicans itself as the host with components that are compatible for use in this organism. The functionality of this two-hybrid system was shown by successful interaction assays with the protein pairs Kis1–Snf4 and Ino4-Ino2. We further confirmed interactions between components of the filamentation/mating MAP kinase pathway, including the unsuspected interaction between the MAP kinases Cek2 and Cek1. We conclude that this system can be used to enhance our knowledge of protein–protein interactions in C. albicans.     

The Evolution of Multivariate Maternal Effects

There is a growing interest in predicting the social and ecological contexts that favor the evolution of maternal effects. Most predictions focus, however, on maternal effects that affect only a single character, whereas the evolution of maternal effects is poorly understood in the presence of suites of interacting traits. To overcome this, we simulate the evolution of multivariate maternal effects (captured by the matrix M) in a fluctuating environment. We find that the rate of environmental fluctuations has a substantial effect on the properties of M: in slowly changing environments, offspring are selected to have a multivariate phenotype roughly similar to the maternal phenotype, so that M is characterized by positive dominant eigenvalues; by contrast, rapidly changing environments favor Ms with dominant eigenvalues that are negative, as offspring favor a phenotype which substantially differs from the maternal phenotype. Moreover, when fluctuating selection on one maternal character is temporally delayed relative to selection on other traits, we find a striking pattern of cross-trait maternal effects in which maternal characters influence not only the same character in offspring, but also other offspring characters. Additionally, when selection on one character contains more stochastic noise relative to selection on other traits, large cross-trait maternal effects evolve from those maternal traits that experience the smallest amounts of noise. The presence of these cross-trait maternal effects shows that individual maternal effects cannot be studied in isolation, and that their study in a multivariate context may provide important insights about the nature of past selection. Our results call for more studies that measure multivariate maternal effects in wild populations.     

A double coil chromatin sub-unit model.

A model is proposed for the structure of DNA in chromatin sub-units. Each sub-unit is proposed to contain two turns of an inner coil, with a pitch of about 40 A and an external diameter of 70 A. Around the inner coil is wound, in opposite handedness, a slightly larger amount of DNA at a diameter of about 150 A. The total contour length consistent with the electron micrographs and X-ray scattering is 600-700 A, or about 200 base pairs. It is suggested that the inner coil is protein rich and contains all of the histones except H1, which is associated with the outer coil. The double-coil model is consistent with previous biochemical and biophysical studies of chromatin. The existence of 200 and 100 base pair digestion fragments and a 6 to 1 DNA compaction are readily explained. This model is based upon the electron microscopic observation of replicas of frozen chromatin and X-ray and neutron scattering. Structural details of 25 A are preserved and visualized by the freeze electron microscopy techniques employed.     

Dung beetles as secondary seed dispersers in a temperate grassland

The two-phase dispersal event in which dung beetles move seeds after endozoochory is often assumed to be advantageous for plant regeneration. Because seeds are expected to end up in favourable and safe germination sites, it is considered as an example of directed dispersal. However, literature so far is restricted to tropical rain forest ecosystems, while data for temperate regions are lacking. In this study, the effect of dung beetles on seedling establishment of endozoochorically dispersed seeds is evaluated for a temperate grassland ecosystem. We performed a field experiment in which cages excluded dung beetles from horse and cattle dung samples with mixed-in grass seeds. Seed germination from these samples was significantly higher than that from samples which were accessible to dung beetles. This indicates that the effect of dung beetles on short-term seedling establishment was negative, which contrasts with the patterns found for large-seeded species used in tropical studies. This is most likely attributed to the lack of roller species and the larger depth at which tunneling Geotrupes species bury seeds.