Preferential cross-linking of the small subunit of the electron-transfer flavoprotein to general acyl-CoA dehydrogenase.

The interaction between pig liver mitochondrial electron-transfer flavoprotein (ETF) and general acyl-CoA dehydrogenase (GAD) was investigated by means of the heterobifunctional reagent N-succinimidyl 3-(2-pyridyldithio)propionate. Neither ETF or GAD contained reactive thiol groups. The substitution of 9.4 lysine residues/FAD group in GAD with pyridyl disulphide structures did not affect the catalytic activity of the enzyme. Thiol groups were introduced into ETF by thiolation with methyl 4-mercaptobutyrimidate. ETF containing 10.5 reactive thiol groups/FAD group showed undiminished electron-acceptor activity with respect to GAD. The reaction of thiolated ETF and GAD containing pyridyl disulphide structures resulted in a decreased staining intensity of the small subunit of ETF on SDS/polyacrylamide-gel electrophoresis. Preferential cross-linking of the smaller subunit of ETF to GAD did not take place when ETF was first treated with SDS, but was unaffected by reduction of GAD by octanoyl-CoA.     

On the presence of a novel covalently bound oxidation-reduction cofactor,iron and labile sulfur in trimethylamine dehydrogenase

Trimethylamine dehydrogenase from a facultative methylotroph contains 4 g atoms each of Fe and S and an unknown, covalently bound, yellow coenzyme. The absorbance of the enzyme in the visible range (λmax=445 nm) is extensively bleached by dithionite. Reduction by substrate causes less extensive bleaching and the appearance of a three banded spectrum which may be representative of a free radical form. Denaturation liberates the FeS center(s) but not the organic coenzyme. The latter is covalently linked to the protein via an amino acid residue and is solubilized on proteolytic digestion in the form of the peptide. The coenzyme-peptide has been purified to a constant ratio of amino acid to coenzyme. The oxidized and reduced forms show maximal absorbance at 437 nm and 380 nm respectively. Based on dithionite titrations its molar absorbance at 437 nm is 12,300 in the oxidized and 4000 in the dithionite reduced form. The cofactor is very labile to photolysis giving rise to several products the predominant one of which shows fluorescence excitation and emission maxima at 394 and 500 nm, respectively. After cleavage of the hydrolyzable amino acids in HCl, the compound consumed 3 moles of periodate. Digestion with aminopeptidase M yields a compound with a single amino acid and ～1 mole of organic P present. Acid phosphatase, but not nucleotide pyrophosphatase affects its mobility. These findings suggest that the coenzyme-peptide is isolated in the form of a mononucleotide, containing a 5-carbon alcohol. The physical and chemical properties of the compound do not agree with those of known flavin or pyridoxine derivatives but are not incompatible with a covalently linked pteridine (lumazine) derivative, although no proof for such a structure is so far available.     

Risk of Cerebral Palsy and Childhood Epilepsy Related to Infections before or during Pregnancy

Background and Aim

Maternal infections during pregnancy have been associated with several neurological disorders in the offspring. However, given the lack of specificity for both the exposures and the outcomes, other factors related to infection such as impaired maternal immune function may be involved in the causal pathway. If impaired maternal immune function plays a role, we would expect infection before pregnancy to be associated with these neurological outcomes.

Methods/Principal Findings

The study population included all first-born singletons in Denmark between January 1 1982 and December 31 2004. We identified women who had hospital-recorded infections within the 5 year period before pregnancy, and women who had hospital-recorded infections during pregnancy. We grouped infections into either infections of the genitourinary system, or any other infections. Cox models were used to estimate adjusted hazard ratios (aHRs) with 95% confidence interval (CI). Maternal infection of the genitourinary system during pregnancy was associated with an increased risk of cerebral palsy (aHR = 1.63, 95% CI: 1.34–1.98) and epilepsy (aHR = 1.27, 95% CI: 1.13–1.42) in the children, compared to children of women without infections during pregnancy. Among women without hospital-recorded infections during pregnancy, maternal infection before pregnancy was associated with an increased risk of epilepsy (aHR = 1.35, 95% CI: 1.21–1.50 for infections of the genitourinary system, and HR = 1.12, 95% CI: 1.03–1.22 for any other infections) and a slightly higher risk of cerebral palsy (aHR = 1.20, 95% CI: 0.96–1.49 for infections of the genitourinary system, and HR = 1.23, 95% CI: 1.06–1.43 for any other infections) in the children, compared to children of women without infections before (and during) pregnancy.

Conclusions

These findings indicate that the maternal immune system, maternal infections, or factors related to maternal immune function play a role in the observed associations between maternal infections before pregnancy and cerebral diseases in the offspring.     

Mutualism and asexual reproduction influence recognition genes in a fungal symbiont

Mutualism between microbes and insects is common and alignment of the reproductive interests of microbial symbionts with this lifestyle typically involves clonal reproduction and vertical transmission by insect partners. Here the Amylostereum fungus–Sirex woodwasp mutualism was used to consider whether their prolonged association and predominance of asexuality have affected the mating system of the fungal partner. Nucleotide information for the pheromone receptor gene rab1, as well as the translation elongation factor 1α gene and ribosomal RNA internal transcribed spacer region were utilized. The identification of rab1 alleles in Amylostereum chailletii and Amylostereum areolatum populations revealed that this gene is more polymorphic than the other two regions, although the diversity of all three regions was lower than what has been observed in free-living Agaricomycetes. Our data suggest that suppressed recombination might be implicated in the diversification of rab1, while no evidence of balancing selection was detected. We also detected positive selection at only two codons, suggesting that purifying selection is important for the evolution of rab1. The symbiotic relationship with their insect partners has therefore influenced the diversity of this gene and influenced the manner in which selection drives and maintains this diversity in A. areolatum and A. chailletii.     

Cryptic speciation in Fusarium subglutinans

Fusarium isolates that form part of the Gibberella fujikuroi species complex have been classified using either a morphological, biological, or phylogenetic species concept. Problems with the taxonomy of Fusarium species in this complex are mostly experienced when the morphological and biological species concepts are applied. The most consistent identifications are obtained with the phylogenetic species concept. Results from recent studies have presented an example of discordance between the biological and phylogenetic species concepts, where a group of F. subglutinans sensu stricto isolates, i.e., isolates belonging to mating population E of the G. fujikuroi complex, could be sub-divided into more than one phylogenetic lineage. The aim of this study was to determine whether this sub-division represented species divergence or intraspecific diversity in F. subglutinans. For this purpose, we included 29 F. subglutinans isolates belonging to the E-mating population that were collected from either maize or teosinte, from a wide geographic range. DNA sequence data for six nuclear regions in each of these isolates were obtained and used in phylogenetic concordance analyses. These analyses revealed the presence of two major groups representing cryptic species in F. subglutinans. These cryptic species were further sub-divided into a number of smaller groups that appear to be reproductively isolated in nature. This suggests not only that the existing F. subglutinans populations are in the process of divergence, but also that each of the resulting lineages are undergoing separation into distinct taxa. These divergences did not appear to be linked to geographic origin, host, or phenotypic characters such as morphology.     

Species-specific primers for Fusarium redolens and a PCR-RFLP technique to distinguish among three clades of Fusarium oxysporum

The currently available morphological and molecular diagnostic techniques for Fusarium redolens and the three phylogenetic clades of Fusarium oxysporum are problematic. Aligned translation elongation factor 1 alpha (TEF-1 alpha) gene sequences from these species and their close relatives were used to design F. redolens-specific primers, and to identify restriction sites that discriminate among the three clades of F. oxysporum. The F. redolens-specific primers distinguished this species from all others included in the study. There were three TEF-1 alpha-RFLP patterns among formae speciales of F. oxysporum. These PCR-RFLP patterns corresponded with the three clades. These techniques provide simple and inexpensive diagnostic methods for the identification of F. redolens and members of the three clades of F. oxysporum.     

Climatic change and its ecological implications at a subantarctic island

Summary Marion Island (47°S, 38°E) has one of the most oceanic climates on earth, with consistently low air temperatures, high precipitation, constantly high humidity, and low incident radiation. Since 1968 mean surface air temperature has increased significantly, by 0.025° C year^–1. This was strongly associated with corresponding changes in sea surface temperature but only weakly, or not at all, with variations in radiation and precipitation. We suggest that changing sealevel (atmospheric and oceanic) circulation patterns in the region underlie all of these changes. Sub-Antarctic terrestrial ecosystems are characterized by being species-poor and having a simple trophic structure. Marion Island is no exception and a scenario is presented of the implications of climatic change for the structure and functioning of its ecosystem. Primary production on the island is high and consequently the vegetation has a large annual requirement for nutrients. There are no macroherbivores and even the insects play only a small role as herbivores, so most of the energy and nutrients incorporated in primary production go through a detritus, rather than grazing, cycle. Ameliorating temperatures and increasing CO₂ levels are expected to increase productivity and nutrient demand even further. However, most of the plant communities occur on soils which have especially low available levels of nutrients and nutrient mineralization from organic reserves is the main bottleneck in nutrient cycling and primary production. Increasing temperatures will not significantly enhance microbially-mediated mineralization rates since soil microbiological processes on the island are strongly limited by waterlogging, rather than by temperature. The island supports large numbers of soil macro-arthropods, which are responsible for most of the nutrient release from peat and litter. The activities of these animals are strongly temperature dependent and increasing temperature will result in enhanced nutrient availability, allowing the potential for increased primary production due to elevated temperature and CO₂ levels to be realized. However, housemice occur on the island and have an important influence on the ecosystem, mainly by feeding on soil invertebrates. The mouse population is strongly temperature-limited and appears to be increasing, possibly as a result of ameliorating temperatures. We suggest that an increasing mouse population, through enhanced predation pressure on soil invertebrates, will decrease overall rates of nutrient cycling and cause imbalances between primary production and decomposition. This, along with more direct effects of mice (e.g. granivory) has important implications for vegetation succession and ecosystem structure and functioning on the island. Some of these are already apparent from comparisons with nearby Prince Edward Island where mice do not occur. Other implications of climatic change for the island are presented which emphasize the very marked influences that invasive organisms have on ecosystem structure and functioning. We suggest that changing sealevel circulation patterns, by allowing opportunities for colonization by new biota, may have an even more important influence on terrestrial sub-Antarctic ecosystems than is suggested merely on the basis of associated changes in temperature or precipitation.