Combined effects of selected Penicillium mycotoxins on in vitro proliferation of porcine lymphocytes

The in vitro effect of combinations of the Penicillium mycotoxins citrinin (CIT), cyclopiazonic acid (CPA), ochratoxin A (OTA), patulin (PAT), penicillic acid (PIA) and roquefortine C (RQC) on mitogen induced lymphocyte proliferation was determined using purified lymphocytes from six piglets. Dose–response curves for each mycotoxin and mycotoxin combinations were generated. The combined effects of toxin pairs based on IC₂₀ were illustrated in isobole diagrams and statistically calculated. OTA and CIT elicited a synergistic effect. Four toxin pairs elicited additive effects, four pairs less–than–additive effects and six pairs independent effects. Thus, the majority of toxin pairs tested produced lower combined effects than an additive effect. The results indicate that the sum effect of all toxins is less than that from the summation of concentrations of the individual compounds, adjusted for differences in potencies.     

Intensity-based analysis of two-colour microarrays enables efficient and flexible hybridization designs

In two-colour microarrays, the ratio of signal intensities of two co-hybridized samples is used as a relative measure of gene expression. Ratio-based analysis becomes complicated and inefficient in multi-class comparisons. We therefore investigated the validity of an intensity-based analysis procedure. To this end, two different cRNA targets were hybridized together, separately, with a common reference and in a self-self fashion on spotted 65mer oligonucleotide microarrays. We found that the signal intensity of the cRNA targets was not influenced by the presence of a target labelled in the opposite colour. This indicates that targets do not compete for binding sites on the array, which is essential for intensity-based analysis. It is demonstrated that, for good-quality arrays, the correlation of signal intensity measurements between the different hybridization designs is high (R > 0.9). Furthermore, ratio calculations from ratio- and intensity-based analyses correlated well (R > 0.8). Based on these results, we advocate the use of separate intensities rather than ratios in the analysis of two-colour long-oligonucleotide microarrays. Intensity-based analysis makes microarray experiments more efficient and more flexible: It allows for direct comparisons between all hybridized samples, while circumventing the need for a reference sample that occupies half of the hybridization capacity.     

Rhizoremediation: a beneficial plant-microbe interaction

Worldwide, contamination of soil and ground water is a severe problem. The negative effects of pollutants on the environment and on human health are diverse and depend on the nature of the pollution. The search for alternative methods for excavation and incineration to clean polluted sites resulted in the application of bioremediation techniques. In this review, we describe some generally accepted bioremediation tools and subsequently focus on the combination of two approaches, phytoremediation and bioaugmentation, resulting in rhizoremediation. During rhizoremediation, exudates derived from the plant can help to stimulate the survival and action of bacteria, which subsequently results in a more efficient degradation of pollutants. The root system of plants can help to spread bacteria through soil and help to penetrate otherwise impermeable soil layers. The inoculation of pollutant-degrading bacteria on plant seed can be an important additive to improve the efficiency of phytoremediation or bioaugmentation.     

A highly Ca2+-sensitive pool of vesicles contributes to linearity at the rod photoreceptor ribbon synapse

Studies of the properties of synaptic transmission have been carried out at only a few synapses. We analyzed exocytosis from rod photoreceptors with a combination of physiological and ultrastructural techniques. As at other ribbon synapses, we found that rods exhibited rapid kinetics of release, and the number of vesicles in the releasable pool is comparable to the number of vesicles tethered at ribbon-style active zones. However, unlike other previously studied neurons, we identified a highly Ca(2+)-sensitive pool of releasable vesicles with a relatively shallow relationship between the rate of exocytosis and [Ca(2+)](i) that is nearly linear over a presumed physiological range of intraterminal [Ca(2+)]. The low-order [Ca(2+)] dependence of release promotes a linear relationship between Ca(2+) entry and exocytosis that permits rods to relay information about small changes in illumination with high fidelity at the first synapse in vision.     

Ecophysiological adaptations of black spruce (<Emphasis Type="Italic"> Picea mariana</Emphasis>) and tamarack (<Emphasis Type="Italic"> Larix laricina</Emphasis>) seedlings to flooding

Black spruce [ Picea mariana (Mill.) B.S.P.] and tamarack [ Larix laricina (Du Roi) K. Koch] are the predominant tree species in boreal peatlands. The effects of 34 days of flooding on morphological and physiological responses were investigated in the greenhouse for black spruce and tamarack seedlings in their second growing season (18 months old). Flooding resulted in reduced root hydraulic conductance, net assimilation rate and stomatal conductance and increased needle electrolyte leakage in both species. Flooded tamarack seedlings maintained a higher net assimilation rate and stomatal conductance compared to flooded black spruce. Flooded tamarack seedlings were also able to maintain higher root hydraulic conductance compared to flooded black spruce seedlings at a comparable time period of flooding. Root respiration declined in both species under flooding. Sugar concentration increased in shoots while decreasing in roots in both species under flooding. Needles of flooded black spruce appeared necrotic and electrolyte leakage increased over time with flooding and remained significantly higher than in flooded tamarack seedlings. No visible damage symptoms were observed in flooded tamarack seedlings. Flooded tamarack seedlings developed adventitious roots beginning 16 days after the start of flooding treatment. Adventitious roots exhibited significantly higher root hydraulic conductivity than similarly sized flooded tamarack roots. Flooded black spruce lacked any such morphological adaptation. These results suggest that tamarack is better able to adjust both morphologically and physiologically to prolonged soil flooding than black spruce seedlings.     

A prevalent POLG CAG microsatellite length allele in humans and African great apes

The human nuclear gene for the catalytic subunit of mitochondrial DNA polymerase (POLG) contains within its coding region a CAG microsatellite encoding a polyglutamine repeat. Previous studies demonstrated an association between length variation at this repeat and male infertility, suggesting a mechanism whereby the prevalent (CAG)₁₀ allele, which occurs at a frequency of >80% in different populations, could be maintained by selection. Sequence analysis of the POLG CAG microsatellite region of more than 1000 human chromosomes reveals that virtually all allelic variation at the locus is accounted for by length variation of the CAG repeat. Analysis of POLG from African great apes shows that a prevalent length allele is present in each species, although its exact length is species-specific. In common chimpanzee (Pan troglodytes) a number of different sequence variants contribute to the prevalent length allele, strongly supporting the idea that the length of the POLG microsatellite region, rather than its exact nucleotide or amino acid sequence, is what is maintained. Analysis of POLG in other primates indicates that the repeat has expanded from a shorter, glutamine-rich sequence, present in the common ancestor of Old and New World monkeys.     

Characterization of two Pseudomonas putida lipopeptide biosurfactants, putisolvin I and II, which inhibit biofilm formation and break down existing biofilms

Pseudomonas putida strain PCL1445 was isolated from roots of plants, grown on a site polluted with polycyclic aromatic hydrocarbons. PCL1445 produces biosurfactant activity at the end of the exponential growth phase. High-performance liquid chromatography (HPLC) analysis of supernatant extracts of PCL1445 showed two peaks with surface-tension reducing activity, tentatively assigned as biosurfactants putisolvin I and putisolvin II and was followed by structural analyses. A transposon mutant of PCL1445, strain PCL1436, which lacks the two surface-active peaks appeared to be mutated in an open reading frame (ORF) with amino acid homology to various lipopeptide synthetases. Structural analyses of the two biosurfactants of PCL1445 revealed that both are novel cyclic lipodepsipeptides with a hexanoic lipid chain connected to the N-terminus of a 12-amino-acid peptide moiety, in which the C-terminal carboxylic acid group forms an ester with the hydroxyl side-chain of Ser9. The difference between the two structures is located in the second amino acid from the C-terminus, being valine for putisolvin I, and leucine/isoleucine for putisolvin II. We show that these novel compounds lower the surface tension and influence the biofilm development on polyvinyl chloride (PVC). Biofilm formation of the bio-synthetic mutant PCL1436 was strongly increased containing more cells, which formed aggregates earlier as compared with wild-type PCL1445 biofilms. Using purified putisolvin I and II it was shown that biofilm formation of different Pseudomonas strains was inhibited and most interestingly, that both putisolvins are also able to break down existing Pseudomonas biofilms.     

Ablation of renin-expressing juxtaglomerular cells results in a distinct kidney phenotype

Renin-expressing cells are peculiar in that they act as differentiated cells, producing the hormone renin, while they also seem to act as progenitors for other renal cell types. As such, they may have functions independent of their ability to generate renin/angiotensin. To test this hypothesis, we ablated renin-expressing cells during development by placing diphtheria toxin A chain (DTA) under control of the Ren1d mouse renin promoter by homologous recombination in a two-renin gene strain (Ren2 and Ren1d). Renin-expressing cells are essentially absent from kidneys in homozygotes (DTA/DTA) which, unlike wild-type mice, are unable to recruit renin-expressing cells when homeostasis is threatened. In contrast, renin staining in the submandibular gland (SMG), which expresses mainly Ren2, is normal. Homozygous mice survive normally, but the kidneys are small and have morphological abnormalities: 25% of the glomeruli are hyperplastic or atrophic, tubules are dilated and atrophic, and areas of undifferentiated cells exist near the atrophic glomeruli and tubules. However, in contrast to the very abnormal renal vessels found when renin-angiotensin system genes are deleted, the kidney vessels in homozygotes have normal wall thickness and no decrease in lumen size. Homozygotes have severely reduced kidney and plasma renin concentrations and females have reduced blood pressure. Homozygotes have elevated blood urea nitrogen and potassium levels, which are suggestive of altered renal function. We conclude that renin cells per se are necessary for the morphological integrity of the kidney and may have a role in maintenance of normal kidney function.     

Cerebral carbohydrate cost of physical exertion in humans

Above a certain level of cerebral activation the brain increases its uptake of glucose more than that of O(2), i.e., the cerebral metabolic ratio of O(2)/(glucose + 12 lactate) decreases. This study quantified such surplus brain uptake of carbohydrate relative to O(2) in eight healthy males who performed exhaustive exercise. The arterial-venous differences over the brain for O(2), glucose, and lactate were integrated to calculate the surplus cerebral uptake of glucose equivalents. To evaluate whether the amount of glucose equivalents depends on the time to exhaustion, exercise was also performed with beta(1)-adrenergic blockade by metoprolol. Exhaustive exercise (24.8 +/- 6.1 min; mean +/- SE) decreased the cerebral metabolic ratio from a resting value of 5.6 +/- 0.2 to 3.0 +/- 0.4 (P < 0.05) and led to a surplus uptake of glucose equivalents of 9 +/- 2 mmol. beta(1)-blockade reduced the time to exhaustion (15.8 +/- 1.7 min; P < 0.05), whereas the cerebral metabolic ratio decreased to an equally low level (3.2 +/- 0.3) and the surplus uptake of glucose equivalents was not significantly different (7 +/- 1 mmol; P = 0.08). A time-dependent cerebral surplus uptake of carbohydrate was not substantiated and, consequently, exhaustive exercise involves a brain surplus carbohydrate uptake of a magnitude comparable with its glycogen content.