Biochemistry of hexose and pentose transformations in soil analyzed by position-specific labeling and 13C-PLFA

Microbial transformations are key processes of soil organic matter (SOM) formation, stabilization and decomposition. Combination of position-specific ¹³C labeling with compound-specific ¹³C-PLFA analysis is a novel tool to trace metabolic pathways. This combination was used to analyze short-term transformations (3 and 10 days after tracer application) of two key monosaccharides: glucose and ribose in soil under field conditions. Transformations of sugars were quantified by the incorporation of ¹³C from individual molecule positions in bulk soil, microbial biomass (by CFE) and in cell membranes of microbial groups classified by ¹³C-PLFA.The ¹³C incorporation in the Gram negative bacteria was higher by one order of magnitude compared to all other microbial groups. All of the ¹³C recovered in soil on day 3 was allocated in microbial biomass. On day 10 however, a part of the ¹³C was recovered in non-extractable microbial cell components or microbial excretions. As sugars are not absorbed by mineral particles due to a lack of charged functional groups, their quick mineralization from soil solution is generally expected. However, microorganisms transformed sugars to metabolites with a slower turnover. The ¹³C incorporation from the individual glucose positions into soil and microbial biomass showed that the two main glucose utilizing pathways in organisms – glycolysis and the pentose phosphate pathway – exist in soils in parallel. However, the pattern of ¹³C incorporation from individual glucose positions into PLFAs showed intensive recycling of the added ¹³C via gluconeogenesis and a mixing of both glucose utilizing pathways. The pattern of position-specific incorporation of ribose C also shows initial utilization in the pentose phosphate pathway but is overprinted on day 10, again due to intensive recycling and mixing. This shows that glucose and ribose – as ubiquitous substrates – are used in various metabolic pathways and their C is intensively recycled in microbial biomass.Analyzing the fate of individual C atoms by position-specific labeling deeply improves our understanding of the pathways of microbial utilization of sugars (and other compounds) by microbial groups and so, of soil C fluxes.     

The effects of a temperature rise on oxygen consumption and energy budget in gilthead sea bream

The rates of daily average, minimum and maximum oxygen consumption, specific dynamic action (SDA), ingestion and digestibility in gilthead sea bream, Sparus auratus L., were measured before, during and after a gradual rise of water temperature from 20 to 28 °C at a rate of 1 °C day-1. The relationship between energy gain and the metabolic costs has also been investigated. Oxygen consumption of juvenile sea bream had a clear daily rhythmicity, with low levels during darkness and higher levels during the light period. Both light and feeding processes raised the metabolism of sea bream, but fish fasted for 2 days also showed an increase in oxygen consumption during the light period. Acclimation to 28 °C was complete for the minimum oxygen consumption rate in 12 days, but daily average and maximum oxygen consumption rates on the 19th day after the change were still 33% higher than at 20 °C mainly due to increased SDA. The digestibility of food components did not change significantly throughout the experiment. These relationships are discussed with respect to the potential for growth when fish are reared at 28 °C, although the energy costs are high.     

Metabolic characterization of tomato fruit during preharvest development, ripening, and postharvest shelf-life

Tomato is an important crop in terms of its economic and nutritional value. Tomato fruit quality is a function of metabolite content, which is prone to physiological changes related to fruit development and ripening. The aim of this work was to use a metabolomic approach to characterize compositional changes (sugars, acids and amino acids) of tomato during preharvest fruit development, ripening, and postharvest shelf-life. Gas chromatography-mass spectrometry was used to identify both polar and volatile metabolites that were involved in fruit development and ripening. Characteristic metabolites for the various fruit developmental stages were identified. Mannose, citramalic, gluconic and keto-l-gulonic acids were shown to be strongly correlated to final postharvest stages. During on-vine ripening, an increase was observed for the major hexoses, glucose and fructose, cell wall components such as galacturonic acid, and for amino acids such as aspartic, glutamic acid and methionine. Major changes were also observed at the level of the TCA cycle, showing a decrease in malic and fumaric acids, and accumulation of citric acid.     

Metabolic resistance mechanisms to phosalone in the common pistachio psyllid, Agonoscena pistaciae (Hem.: Psyllidae)

The common pistachio psyllid, Agonoscena pistaciae, is the most damaging pest of pistachio in Iran, and is generally controlled by insecticides belonging to various classes especially, phosalone. The toxicity of phosalone in nine populations of the pest was assayed using the residual contact vial and insect-dip methods. The bioassay results showed significant discrepancy in susceptibility to phosalone among the populations. Resistance ratio of the populations to the susceptible population ranged from 3.3 to 11.3. The synergistic effects of TPP, PBO and DEM were evaluated on the susceptible and the most resistant population to determine the involvement of esterases, mixed function oxidases and glutathione S-transferases in resistance mechanisms, respectively. The level of resistance to phosalone in the resistant population was suppressed by TPP, PBO and DEM, suggesting that the resistance to phosalone is mainly caused by esterase detoxification. Biochemical enzyme assays revealed that esterase, glutathione S-transferase and cytochrome P450 monooxygenase activities in the resistant population was higher than that in the susceptible. Glutathione-S-transferases play a minor role in the resistance of the pest to phosalone.     

Microbial diversity in three floodplain soils at the Elbe River (Germany)

Microbial communities in floodplain soils are exposed to periodical flooding. A long-term submerged Eutric Gleysol (GLe), an intermediate flooded Eutric Fluvisol (FLe), and a short-time flooded Mollic Fluvisol (FLm) at the Elbe River (Germany) with similar organic carbon contents (C_org) between 8.1% and 8.9% were selected to test the quality of phospholipid fatty acids (PLFA), soil microbial carbon (C_mic), basal respiration (BR), metabolic quotient (qCO₂), and C_mic/C_org ratio to characterize and discriminate these soils with microbial parameters.The three floodplain soils can be differentiated by C_mic and by total PLFA-biomass. Due to the different flooding durations and the time since the soils were last flooded C_mic and PLFA-biomass increase in the order GLe<FLe<FLm. Both parameters correlate significantly (r=0.999;p<0.05). The C_mic/C_org ratios are low in comparison to terrestrial soils and revealed the same ranking over the three soils like C_mic. Contrary, qCO₂ and BR are highest in GLe and lowest in FLm according to inundation regime. The diminished C_mic, high BR, and high qCO₂ values in GLe seem to be an unspecific response of aerobic soil microorganisms on the long flooding period and the resulting short time for developing after last flooding as well as the low pH value. Different plant communities and their residues may influence the microbial diversity additionally.The PLFA profiles were dominated by the group of saturated fatty acids that together constituted almost 62-72% of the total fatty acids identified in the soils. In GLe all groups of PLFA, inclusive monounsaturated fatty acids, are lowest and in FLm highest, while in FLe the PLFA fractions show an intermediary amount of the three soils. The FLm had most of the time aerobic conditions and revealed therefore the highest C_mic, PLFA-biomass, especially monounsaturated fatty acids, C_mic/C_org ratio as well as relatively low BR and qCO₂ value. These indicate that microorganisms in FLm are more efficiently in using carbon sources than those in GLe and FLe.All 26 identified PLFA were found in FLe and FLm, while the polyunsaturated fungi biomarker 18:2ω6,9c could not be detected in GLe. In this long-time submerged soil the environmental conditions which microorganisms are exposed might be disadvantageous for fungi.     

Microbial decomposition of skeletal muscle tissue (Ovis aries) in a sandy loam soil at different temperatures

A laboratory experiment was conducted to determine the effect of temperature (2, 12, 22 °C) on the rate of aerobic decomposition of skeletal muscle tissue (Ovis aries) in a sandy loam soil incubated for a period of 42 days. Measurements of decomposition processes included skeletal muscle tissue mass loss, carbon dioxide (CO₂) evolution, microbial biomass, soil pH, skeletal muscle tissue carbon (C) and nitrogen (N) content and the calculation of metabolic quotient (qCO₂). Incubation temperature and skeletal muscle tissue quality had a significant effect on all of the measured process rates with 2 °C usually much lower than 12 and 22 °C. Cumulative CO₂ evolution at 2, 12 and 22 °C equaled 252, 619 and 905 mg CO₂, respectively. A significant correlation (P<0.001) was detected between cumulative CO₂ evolution and tissue mass loss at all temperatures. Q₁₀s for mass loss and CO₂ evolution, which ranged from 1.19 to 3.95, were higher for the lower temperature range (Q₁₀(2-12 °C)>Q₁₀(12-22 °C)) in the Ovis samples and lower for the low temperature range (Q₁₀(2-12 °C)<Q₁₀(12-22 °C)) in the control samples. Metabolic quotient and the positive relationship between skeletal muscle tissue mass loss and cumulative CO₂ evolution suggest that tissue decomposition was most efficient at 2 °C. These phenomena may be due to lower microbial catabolic requirements at lower temperature.     

P2Y12 receptor gene mutation associated with postoperative hemorrhage in a Greater Swiss Mountain dog

A novel hereditary disorder of platelets was identified across 5 generations of a family of Greater Swiss Mountain dogs. The first dog identified with the mutation bled excessively following routine ovariohysterectomy and required multiple transfusions. Coagulation screening assays, platelet counts, and von Willebrand factor antigen activity were within reference intervals. Flow cytometric studies indicated that platelets from the affected dog expressed normal levels of glycoproteins IIb and IIIa and responded to 2 platelet-activating agents, convulxin and platelet-activating factor, but not to ADP. Based on DNA studies, a 3 base-pair deletion predicted to result in elimination of a serine from the extracellular domain was identified in the gene encoding P2Y12, an ADP receptor protein located on platelet membranes. Flow cytometric analysis of platelets and studies of DNA performed concurrently on 2 unrelated Greater Swiss Mountain dogs were unremarkable. The mutation was subsequently identified in the sire, the maternal grand-dam, a maternal great grandparent, a paternal great grandparent, and a great-great grandparent. The sire was homozygous, but had not yet been identified as having a hemostatic disorder; the other 4 dogs were carriers. This is the first report of a mutation in the gene encoding the ADP receptor P2Y12 in a domestic animal. P2Y12 is the same receptor targeted by ticlopidine and clopidogrel, platelet inhibitors used in lieu of aspirin in people at risk for cardiovascular disease; thus, spontaneous bleeding is not expected unless there are other contributing factors. This disorder is particularly troublesome because spontaneous hemorrhage is absent to mild in affected dogs; however, following routine surgical procedures or trauma, excessive bleeding could occur and have possible fatal consequences.