An SOS response induced by high pressure in Escherichia coli

Although pressure is an important environmental parameter in microbial niches such as the deep sea and is furthermore used in food preservation to inactivate microorganisms, the fundamental understanding of its effects on bacteria remains fragmentary. Our group recently initiated differential fluorescence induction screening to search for pressure-induced Escherichia coli promoters and has already reported induction of the heat shock regulon. Here the screening was continued, and we report for the first time that pressure induces a bona fide SOS response in E. coli, characterized by the RecA and LexA-dependent expression of uvrA, recA, and sulA. Moreover, it was shown that pressure is capable of triggering lambda prophage induction in E. coli lysogens. The remnant lambdoid e14 element, however, could not be induced by pressure, as opposed to UV irradiation, indicating subtle differences between the pressure-induced and the classical SOS response. Furthermore, the pressure-induced SOS response seems not to be initiated by DNA damage, since DeltarecA and lexA1 (Ind-) mutants, which are intrinsically hypersensitive to DNA damage, were not sensitized or were only very slightly sensitized for pressure-mediated killing and since pressure treatment was not found to be mutagenic. In light of these findings, the current knowledge of pressure-mediated effects on bacteria is discussed.     

Auxin-induced elongation of short maize coleoptile segments is supported by 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one

Endogenous extractable factors associated with auxin action in plant tissues were investigated, especially their effects on elongation of 1-mm coleoptile segments of maize (Zea mays L.), in the presence of saturating 10 μM indole-3-acetic acid (IAA). The relative growth response, to auxin alone, was much smaller in segments shorter than 2–3 mm compared to 10-mm segments. Fusicoccin-induced elongation, however, was less affected by shortening the segments. A reduced auxin response may result from the depletion through cut surfaces of a substance required for IAA-mediated growth. Sucrose, phenolics like flavonoids, and vitamins were ruled out as the causal factors. A partially purified methanol extract of maize coleoptiles supported long-term, auxin-controlled elongation. The active material was also found among substances bleeding from scrubbed maize coleoptiles. The active factor from maize was further purified by HPLC and characterised by the UV spectrum and its pH shift. This factor was identified as 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) by mass spectroscopy. Activity tests confirmed that pure DIMBOA from other sources sustained auxin-induced elongation of short maize coleoptile segments. However, DIMBOA only partially restored the activity lost from short segments. This indicates that an additional factor, other than DIMBOA, is required. Extracts from Avena or Cucurbita did not contain the factor DIMBOA; it was active on maize elongation, but not on Avena coleoptiles or Cucurbita hypocotyls. This narrow specificity and the lack of DIMBOA action in short-term tests with maize indicate that DIMBOA is not the general auxin cofactor but may specifically “spare” the co-auxin in maize. Received: 27 June 2000 / Accepted: 16 October 2000     

Carbon cycling in eroding landscapes: geomorphic controls on soil organic C pool composition and C stabilization

Recent studies have highlighted the tight coupling between geomorphic processes and soil carbon (C) turnover and suggested that eroding landscapes can stabilize more C than their non‐eroding counterparts. However, large uncertainties remain and a mechanistic understanding of geomorphic effects on C storage in soils is still lacking. Here, we quantified the soil organic carbon (SOC) stock and pool distribution along geomorphic gradients and combined data derived from soil organic matter fractionation and incubation experiments. The size and composition of the SOC pools were strongly related to geomorphic position: 1.6 to 6.2 times more C was stabilized in the subsoils (25–100cm) of depositional profiles than in those of eroding profiles. Subsoil C of depositional profiles is predominantly associated with microaggregates and silt‐sized particles which are associated with pools of intermediate stability. We observed a significantly higher mean residence time for the fast and intermediate turnover pools of buried C at depositional positions, relative to non‐eroding and eroding positions, resulting from the physical protection of C associated with microaggregates and silt particles. Conversely, significant amounts of C were replaced at eroding positions but the lower degree of decomposition and the lack of physically protected C, resulted in higher respiration rates. By considering C cycling at non‐eroding, eroding and depositional positions, we found that the eroding landscapes studied store up to 10% more C due to soil redistribution processes than non‐eroding landscapes. This is the result of the stabilization of C in former subsoil at eroding positions and partial preservation of buried C in pools of intermediate turnover at depositional positions. However, the sink strength was limited by significant losses of buried C as only a small fraction of the C was associated with stable pools.     

Spectral properties of H-reflex recordings after an acute bout of whole-body vibration

Although research supports the use of whole-body vibration (WBV) to improve neuromuscular performance, the mechanisms for these improvements remain unclear. The purpose of this study was to identify the effect of WBV on the spectral properties of electrically evoked H-reflex recordings in the soleus (SOL) muscle. The H-reflex recordings were measured in the SOL muscle of 20 participants before and after a bout of WBV. The H-reflexes were evoked every 15 seconds for 150 seconds after WBV. A wavelet procedure was used to extract spectral data, which were then quantified with a principle components analysis. Resultant principle component scores were used for statistical analysis. The analysis extracted 1 principle component associated with the intensity of the myoelectric spectra and 1 principle component associated with the frequency. The scores of the principle component that were related to the myoelectric intensity were smaller at 30 and 60 milliseconds after WBV than before WBV. The WBV transiently decreased the intensity of myoelectric spectra during electrically evoked contractions, but it did not influence the frequency of the spectra. The decrease in intensity likely indicates a smaller electrically evoked muscle twitch response, whereas the lack of change in frequency would indicate a similar recruitment pattern of motor units before and after WBV.     

Effect of operating and sampling conditions on the exhaust gas composition of small-scale power generators

Small stationary diesel engines, like in generator sets, have limited emission control measures and are therefore responsible for 44% of the particulate matter (PM) emissions in the United States. The diesel exhaust composition depends on operating conditions of the combustion engine. Furthermore, the measurements are influenced by the used sampling method. This study examines the effect of engine loading and exhaust gas dilution on the composition of small-scale power generators. These generators are used in different operating conditions than road-transport vehicles, resulting in different emission characteristics. Experimental data were obtained for gaseous volatile organic compounds (VOC) and PM mass concentration, elemental composition and nitrate content. The exhaust composition depends on load condition because of its effect on fuel consumption, engine wear and combustion temperature. Higher load conditions result in lower PM concentration and sharper edged particles with larger aerodynamic diameters. A positive correlation with load condition was found for K, Ca, Sr, Mn, Cu, Zn and Pb adsorbed on PM, elements that originate from lubricating oil or engine corrosion. The nitrate concentration decreases at higher load conditions, due to enhanced nitrate dissociation to gaseous NO at higher engine temperatures. Dilution on the other hand decreases PM and nitrate concentration and increases gaseous VOC and adsorbed metal content. In conclusion, these data show that operating and sampling conditions have a major effect on the exhaust gas composition of small-scale diesel generators. Therefore, care must be taken when designing new experiments or comparing literature results.     

Cross-linking of wheat gluten proteins during production of hard pretzels

The impact of the hot alkaline dip, prior to pretzel-baking, on the types and levels of cross-links between wheat proteins was studied. Protein extractability of pretzel dough in sodium dodecyl sulfate containing buffer decreased during alkaline dipping [45?s, 1.0% (w/v) NaOH, 90°C], and even more during baking (3?min at 250°C) and drying (10?min at 135°C). Reducing agent increased the extractability partly, indicating that both reducible (disulfide, SS) and non-reducible (non-SS) protein cross-links had been formed. The decrease in cystine levels suggested β-elimination of cystine releasing Cys and dehydroalanine (DHA). Subsequent reaction of DHA with Lys and Cys, induced the unusual and potentially cross-linking amino acids lysinoalanine (LAL) and lanthionine (LAN), respectively, in alkaline dipped dough (7?μmol LAN/g protein) and in the end product (9?μmol LAL and 50?μmol LAN/g protein). The baking/drying step increased sample redness, decreased Lys levels more than expected based on LAL formation (57?μmol/g protein), and induced a loss of reducing sugars (99?μmol/g protein), which suggested the potential contribution of Maillard-derived cross-links to the observed extractability loss. However, levels of Maillard products which possibly cross-link proteins, are small compared to DHA-derived cross-links. Higher dipping temperatures, longer dipping times, and higher NaOH concentrations increased protein extractability losses and redness, as well as LAL and LAN levels in the end product. No indications for Maillard-derived cross-links or LAL in pretzel dough immediately after dipping were found, even when severe dipping conditions were used.