Effect of the oxygen supply on pattern of growth and corrinoid and organic acid production of Propionibacterium shermanii

Propionibacterium shermanii CDB 10014 is able to grow even at high oxygen transfer rates (24.0 mmol O₂ l⁻¹ h⁻¹), in contrast to reports in the specialised literature, where all Propionibacteria are considered oxygen-sensitive microorganisms. Propionic acid is the main product in anaerobiosis. The presence of oxygen in the system leads to an inhibition of propionic acid production while acetic acid formation is enhanced. At high oxygen supply rates no propionic acid is produced and acetic acid is the main product. Lactic acid is also produced in reasonable quantities (2.7 g l⁻¹). The growth rate (μ_max) is higher in anaerobiosis (0.19 h⁻¹) than in aerobiosis (0.12–0.15 h⁻¹). The cell yield is higher in aerobiosis (0.18–0.22 g g⁻¹) than in anaerobiosis (0.14 g g⁻¹) suggesting the oxidative metabolism of glucose by Propionibacterium shermanii CDB 10014. No corrinoid production was detected at oxygen transfer rates of more than 13.6 mmol l⁻¹ h⁻¹. Received: 10 September 1997 / Received revision: 6 January 1998 / Accepted: 9 January 1998     

Implementation and Assessment of an Intervention to Debias Adolescents against Causal Illusions

Researchers have warned that causal illusions are at the root of many superstitious beliefs and fuel many people’s faith in pseudoscience, thus generating significant suffering in modern society. Therefore, it is critical that we understand the mechanisms by which these illusions develop and persist. A vast amount of research in psychology has investigated these mechanisms, but little work has been done on the extent to which it is possible to debias individuals against causal illusions. We present an intervention in which a sample of adolescents was introduced to the concept of experimental control, focusing on the need to consider the base rate of the outcome variable in order to determine if a causal relationship exists. The effectiveness of the intervention was measured using a standard contingency learning task that involved fake medicines that typically produce causal illusions. Half of the participants performed the contingency learning task before participating in the educational intervention (the control group), and the other half performed the task after they had completed the intervention (the experimental group). The participants in the experimental group made more realistic causal judgments than did those in the control group, which served as a baseline. To the best of our knowledge, this is the first evidence-based educational intervention that could be easily implemented to reduce causal illusions and the many problems associated with them, such as superstitions and belief in pseudoscience.     

Pyranose 2-oxidase from Phanerochaete chrysosporium– further biochemical characterisation

Pyranose 2-oxidase (P2O) was purified 43-fold to apparent homogeneity from the basidiomycete Phanerochaete chrysosporium using liquid chromatography on phenyl Sepharose, Mono Q (twice) and phenyl Superose. The native enzyme has a molecular mass of about 250 kDa (based on native PAGE) and is composed of four identical subunits of 65 kDa. It contains three isoforms of isoelectric point (pI) 5.0, 5.05 and 5.15 and does not appear to be a glycoprotein. P2O is optimally stable at pH 8.0 and up to 60 °C. It is active over a broad pH range (5.0–9.0) with maximum activity at pH 8.0–8.5 and at 55 °C, and a broad substrate specificity. d-Glucose is the preferred substrate, but 1-β-aurothioglucose, 6-deoxy-d-glucose, l-sorbose, d-xylose, 5-thioglucose, d-glucono-1,5-lactone, maltose and 2-deoxy-d-glucose are also oxidised at relatively high rates. A Ping Pong Bi Bi mechanism was demonstrated for the P2O reaction at pH 8.0, with a catalytic constant (k _cat) of 111.0 s⁻¹ and an affinity constant (K _m) of 1.43 mM for d-glucose and 83.2 μM for oxygen. Whereas the steady-state kinetics for glucose oxidation were unaffected by the medium at pH ≥ 7.0, at low pH both pH and buffer composition affected the P2O kinetics with the k _cat/K _m value decreasing with decreasing pH. The greatest effect was observed in acetate buffer (0.1 M, pH 4.5), where the k _cat decreased to 60.9 s⁻¹ and the K _m increased to 240 mM. The activity of P2O was completely inhibited by 10 mM HgCl₂, AgNO₃ and ZnCl₂, and 50% by lead acetate, CuCl₂ and MnCl₂. Received: 28 August 1996 / Received revision: 25 November 1996 / Accepted: 29 November 1996     

Succession of bacterivorous protists on laboratory-made marine snow

Colonization and succession over time by bacterivorous protistson laboratory-made marine snow were analysed in five assaysduring 1994. Marine snow was made hom natural seawater usingrolling tanks. In all experiments, the macroaggregates werestable in size and consistency after the fourth day, and thecolonization and succession processes were similar. Newly formedmacre aggregates became colonized by heterotrophic nanoflagellateson the fourth day, mmt of them kinete plastids (Bodo designisand Rhynchomonns nasuta) and bicosoecids (Pseudobodo tremulansand Bicosoeca sp.). Sarcodines and ciliates appeared 1 day later.Among the former, the most abundant genus was Vannella sp.,while scuticociliates (Uronema marinum) and hypotrichs (Euplotesvannus and Aspidisca steini) were the most abundant ciliates.Most of the species observed in the study were more common tobenthic habitats than to pelagic ones. The planktonic existenceof the genera Bodo, Rhynchomonas, Bicosoeca, Euplotes and Aspidiscadepends on the presence of surfaces because they are poor swimmersor immotile, and Pseudobodo and Vannella need attachment forfeeding. The only pelagic protist observed was Uronema, probablybecause its opportunistic behaviour leads it to exploit enrichedenvironments such as marine snow. Flagellate and ciliate abundancesin laboratory-made macroaggregates were much higher than insurrounding water, which indicates that marine snow representsan enhanced habitat for protist growth.     

The Lack of Side Effects of an Ineffective Treatment Facilitates the Development of a Belief in Its Effectiveness

Some alternative medicines enjoy widespread use, and in certain situations are preferred over conventional, validated treatments in spite of the fact that they fail to prove effective when tested scientifically. We propose that the causal illusion, a basic cognitive bias, underlies the belief in the effectiveness of bogus treatments. Therefore, the variables that modulate the former might affect the latter. For example, it is well known that the illusion is boosted when a potential cause occurs with high probability. In this study, we examined the effect of this variable in a fictitious medical scenario. First, we showed that people used a fictitious medicine (i.e., a potential cause of remission) more often when they thought it caused no side effects. Second, the more often they used the medicine, the more likely they were to develop an illusory belief in its effectiveness, despite the fact that it was actually useless. This behavior may be parallel to actual pseudomedicine usage; that because a treatment is thought to be harmless, it is used with high frequency, hence the overestimation of its effectiveness in treating diseases with a high rate of spontaneous relief. This study helps shed light on the motivations spurring the widespread preference of pseudomedicines over scientific medicines. This is a valuable first step toward the development of scientifically validated strategies to counteract the impact of pseudomedicine on society.     

Recurrent seasonal changes in bacterial growth efficiency,metabolism and community composition in coastal waters

The microbial response to environmental changes in coastal waters of the eastern Cantabrian Sea was explored for four years by analysing a broad set of environmental variables along with bacterial community metabolism and composition. A recurrent seasonal cycle emerged, consisting of two stable periods, characterized by low bacterial metabolic activity (winter) from October to March, and high bacterial metabolic activity (summer) from May to August. These two contrasting periods were linked by short transition periods in April (T_A) and September (T_S). The phylogenetic groups Alphaproteobacteria and Bacteroidetes were dominant during winter and summer respectively, and their recurrent alternation was mainly driven by the bloom of eukaryotic phytoplankton before T_A and the bloom of prokaryotic phytoplankton before T_S. Bacterial growth efficiency remained high and stable during the winter and summer periods but dropped during the two short transition periods. Our results suggest that bacterial growth efficiency should be considered a very resilient property that reflects different stages in the adaptation of the bacterial community composition to the environmental changes occurring throughout the seasonal cycle in this coastal ecosystem.     

Imbalanced nutrient recycling in a warmer ocean driven by differential response of extracellular enzymatic activities

Ocean oligotrophication concurrent with warming weakens the capacity of marine primary producers to support marine food webs and act as a CO₂ sink, and is believed to result from reduced nutrient inputs associated to the stabilization of the thermocline. However, nutrient supply in the oligotrophic ocean is largely dependent on the recycling of organic matter. This involves hydrolytic processes catalyzed by extracellular enzymes released by bacteria, which temperature dependence has not yet been evaluated. Here, we report a global assessment of the temperature‐sensitivity, as represented by the activation energies (E_a), of extracellular β‐glucosidase (βG), leucine aminopeptidase (LAP) and alkaline phosphatase (AP) enzymatic activities, which enable the uptake by bacteria of substrates rich in carbon, nitrogen, and phosphorus, respectively. These E_a were calculated from two different approaches, temperature experimental manipulations and a space‐for‐time substitution approach, which generated congruent results. The three activities showed contrasting E_a in the subtropical and tropical ocean, with βG increasing the fastest with warming, followed by LAP, while AP showed the smallest increase. The estimated activation energies predict that the hydrolysis products under projected warming scenarios will have higher C:N, C:P and N:P molar ratios than those currently generated, and suggest that the warming of oceanic surface waters leads to a decline in the nutrient supply to the microbial heterotrophic community relative to that of carbon, particularly so for phosphorus, slowing down nutrient recycling and contributing to further ocean oligotrophication.     

Identification of proteomic signatures of exposure to marine pollutants in mussels (Mytilus edulis)

Bivalves and especially mussels are very good indicators of marine and estuarine pollution, and so they have been widely used in biomonitoring programs all around the world. However, traditional single parameter biomarkers face the problem of high sensitivity to biotic and abiotic factors. In our study, digestive gland peroxisome-enriched fractions of Mytilus edulis (L., 1758) were analyzed by DIGE and MS. We identified several proteomic signatures associated with the exposure to several marine pollutants (diallyl phthalate, PBDE-47, and bisphenol-A). Animals collected from North Atlantic Sea were exposed to the contaminants independently under controlled laboratory conditions. One hundred and eleven spots showed a significant increase or decrease in protein abundance in the two-dimensional electrophoresis maps from the groups exposed to pollutants. We obtained a unique protein expression signature of exposure to each of those chemical compounds. Moreover a set of proteins composed a proteomic signature in common to the three independent exposures. It is remarkable that the principal component analysis of these spots showed a discernible separation between groups, and so did the hierarchical clustering into four classes. The 14 proteins identified by MS participate in alpha- and beta-oxidation pathways, xenobiotic and amino acid metabolism, cell signaling, oxyradical metabolism, peroxisomal assembly, respiration, and the cytoskeleton. Our results suggest that proteomic signatures could become a valuable tool to monitor the presence of pollutants in field experiments where a mixture of pollutants is often present. Further studies on the identified proteins could provide crucial information to understand possible mechanisms of toxicity of single xenobiotics or mixtures of them in marine ecosystems.