Yeast cell mortality related to a high-pressure shift: occurrence of cell membrane permeabilization

The shrinkage of yeast cells caused by high-pressure treatment (250 MPa, 15 min) was investigated using direct microscopic observation. A viable staining method after treatment allowed the volume variation of two populations to be distinguished: an irreversible volume decrease (about 35% of the initial volume) of pressure-inactivated cells during pressure holding time, and viable cells, which were less affected. A mass transfer was then induced during high-pressure treatment. Causes of this transfer seem to be related to a pressure-induced membrane permeabilization, allowing a subsequent leakage of internal solutes, where three ions (Na+, K+ and Ca2+), plus endogenous glycerol, were verified. This glycerol leakage was found to occur after yeast pressurization in a medium having low water activity, although the yeast was not inactivated. All these observations lead to the hypothesis that pressure-induced cell permeabilization could be the cause of yeast inactivation under pressure.     

Architectural specialization of the intrinsic thoracic limb musculature of the American badger (Taxidea taxus)

Evaluation of the relationships between muscle structure and digging function in fossorial species is limited. Badgers and other fossorial specialists are expected to have massive forelimb muscles with long fascicles capable of substantial shortening for high power and applying high out‐force to the substrate. To explore this hypothesis, we quantified muscle architecture in the thoracic limb of the American badger (Taxidea taxus) and estimated the force, power, and joint torque of its intrinsic musculature in relation to the use of scratch‐digging behavior. Architectural properties measured were muscle mass, belly length, fascicle length, pennation angle, and physiological cross‐sectional area. Badgers possess hypertrophied shoulder flexors/humeral retractors, elbow extensors, and digital flexors. The triceps brachii is particularly massive and has long fascicles with little pennation, muscle architecture consistent with substantial shortening capability, and high power. A unique feature of badgers is that, in addition to elbow joint extension, two biarticular heads (long and medial) of the triceps are capable of applying high torques to the shoulder joint to facilitate retraction of the forelimb throughout the power stroke. The massive and complex digital flexors show relatively greater pennation and shorter fascicle lengths than the triceps brachii, as well as compartmentalization of muscle heads to accentuate both force production and range of shortening during flexion of the carpus and digits. Muscles of most functional groups exhibit some degree of specialization for high force production and are important for stabilizing the shoulder, elbow, and carpal joints against high limb forces generated during powerful digging motions. Overall, our findings support the hypothesis and indicate that forelimb muscle architecture is consistent with specializations for scratch‐digging. Quantified muscle properties in the American badger serve as a comparator to evaluate the range of diversity in muscle structure and contractile function that exists in mammals specialized for fossorial habits. J. Morphol. 2013. © 2012 Wiley Periodicals, Inc.     

Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.     

PHYLOGENY AND SYSTEMATICS OF THE MARINE ALGAL FAMILY GRACILARIACEAE (GRACILARIALES,RHODOPHYTA) BASED ON SMALL SUBUNIT rDNA AND ITS SEQUENCES OF ATLANTIC AND PACIFIC SPECIES1

We sequenced the small subunit rDNA and internal transcribed spacer region of Gracilariaceae from the tropical Atlantic and Pacific, with emphasis on flattened or compressed species. Sequence comparisons confirmed three main lineages of Gracilariaceae: Curdiea/Melanthalia, Gracilariopsis/Gracilariophila, and Gracilaria. The Curdiea/Melanthalia diverged early in the family. Gracilariopsis was paraphyletic, because at least one Gracilariophila species evolved from it. The Atlantic Gracilariopsis were monophyletic and separated from the Pacific lineages. The Gracilaria included all species referable to its own species and to Hydropuntia, which was paraphyletic, formed by distantly related lineages. The new combination Gracilaria pauciramosa (N. Rodríguez Ríos) Bellorin, M. C. Oliveira et E. C. Oliveira is proposed for Polycavernosa pauciramosa N. Rodríguez Ríos. Recognition of subgenera within Gracilaria, based on spermatangial arrangement, was not supported. Instead, infrageneric groups were delineated by geographic origins and combinations of reproductive characters. Most Pacific species with either “textorii” or “verrucosa” type spermatangia were deeply separated from Atlantic species. Within the Atlantic Gracilaria, a lineage encompassing mostly tropical cylindrical species with “henriquesiana” type spermatangia and distinctive cystocarp anatomy was recognized. A lineage was also retrieved for cold water stringy species with verrucosa type spermatangia. Several species from the western Atlantic are closely related to Gracilaria tikvahiae McLachlan with nearly identical morphology. On the other hand, most flattened species from the tropical Atlantic were closely related despite their diverse morphologies. The interpretation of our data in addition to the literature indicates that more populations from the Indo‐Pacific must be studied before a general picture of Gracilariaceae evolution can be framed.     

Influence of Water Potential on gamma-Decalactone Production by the Yeast Sporidiobolus salmonicolor

The influence of water potential on gamma-decalactone production by the yeast Sporidiobolus salmonicolor cultivated in a liquid medium was evaluated by gas-chromatographic analysis. Modifications in water potential led to a number of variations in the aroma production. Maximum extracellular production occurred at water activity (a(w)) with a value of 0.99. Further analyses revealed an important phenomenon of cellular accumulation of aroma for a(w) values between 0.97 and 0.99.     

Two-dimensional 1H, 15N NMR investigation of uniformly 15N-labeled lac repressor headpiece.

15N uniformly labeled lac repressor and lac repressor headpiece were prepared. 15N NMR spectra of lac repressor were shown resolution inadequate for detailed study while the data showed that the 15N labeled N-terminal part of the protein is quite suitable for this type of study allowing future investigation of the specific interaction of the lac repressor headpiece with the lac operator. We report here the total assignment of proton 1H and nitrogen 15NH backbone resonances of this headpiece in the free state. Assignments of the 15N resonances of the protein were obtained in a sequential manner using heteronuclear multiple quantum coherence (HMQC), relayed HMQC nuclear Overhauser and relayed HMQC-HOHAHA spectroscopy. More than 80 per cent of residues were assigned by their 15NH(i)-N1H(i + 1) and 15NH(i)-N1H(i - 1) connectivities. Values of the 3JNH alpha splitting for 39 of the 51 residues of the headpiece were extracted from HMQC and HMQC-J. The observed 15NH(i)-C beta H cross peaks and the 3JNH alpha coupling constants values are in agreement with the three alpha-helices previously described [Zuiderweg, E.R.P., Scheek, R.M., Boelens, R., van Gunsteren, W.F. and Kaptein, R., Biochimie 67, 707 (1985)]. The 3JNH alpha coupling constants can be now used for a more confident determination of the lac repressor headpiece. From these values it is shown that the geometry of the ends of the second and third alpha-helices exhibit deviation from the canonical alpha-helix structure. On the basis of NOEs and 3JNH alpha values, the geometry of the turn of the helix-turn-helix motif is discussed.