42 research outputs found
Flocculation onset in Saccharomyces cerevisiae: effect of ethanol, heat and osmotic stress
Aims: To examine the effect of different stress conditions on the onset of flocculation
in an ale-brewing strain, Saccharomyces cerevisiae NCYC 1195.
Methods and Results: Flocculation was evaluated using the method of Soares,
E.V. and Vroman, A. [Journal of Applied Microbiology (2003) 95, 325]; plasma
membrane integrity was accessed using propidium iodide and the staining of
the yeast cell wall was performed using calcofluor white M2R. Cells in exponential
phase of growth were subjected to different stress conditions. The addition
of 1%, 3% and 5% (v/v) ethanol, 1% and 3% (v/v) isopropanol or a brief heat shock (52ÂșC, 5 min), did not induce an early flocculation phenotype when compared with control cells. The addition of 10% (v/v) ethanol, a continuous mild heat-stress (37ÂșC) or an osmotic stress (0.5 or 1 mol l-1 of NaCl) did not induce a flocculent phenotype.
Conclusions: Flocculation seems not to be induced as a response to different
chemical (ethanol and isopropanol) and physical (heat and osmotic) stress conditions.
Conversely, osmotic and ethanol [10% (v/v)] stress, as well as a continuous mild heat shock (37ÂșC), have a negative impact on the phenotype expression of flocculation.
Significance and Impact of the Study: The findings reported here contribute to
the elucidation of the control of yeast flocculation. This information might be
useful to the brewing industry, as the time when the onset of flocculation
occurs can determine the fermentation performance and the beer quality, as
well as in other biotechnological industries where flocculation can be used as a
cell separation process.ERASMUS; ISEP (Portugal)
Schmidt-hammer exposure ages from periglacial patterned ground (sorted circles) in Jotunheimen, Norway, and their interpretative problems
© 2016 Swedish Society for Anthropology and Geography Periglacial patterned ground (sorted circles and polygons) along an altitudinal profile at Juvflya in central Jotunheimen, southern Norway, is investigated using Schmidt-hammer exposure-age dating (SHD). The patterned ground surfaces exhibit R-value distributions with platycurtic modes, broad plateaus, narrow tails, and a negative skew. Sample sites located between 1500 and 1925 m a.s.l. indicate a distinct altitudinal gradient of increasing mean R-values towards higher altitudes interpreted as a chronological function. An established regional SHD calibration curve for Jotunheimen yielded mean boulder exposure ages in the range 6910 ± 510 to 8240 ± 495 years ago. These SHD ages are indicative of the timing of patterned ground formation, representing minimum ages for active boulder upfreezing and maximum ages for the stabilization of boulders in the encircling gutters. Despite uncertainties associated with the calibration curve and the age distribution of the boulders, the early-Holocene age of the patterned ground surfaces, the apparent cessation of major activity during the Holocene Thermal Maximum (HTM) and continuing lack of late-Holocene activity clarify existing understanding of the process dynamics and palaeoclimatic significance of large-scale sorted patterned ground as an indicator of a permafrost environment. The interpretation of SHD ages from patterned ground surfaces remains challenging, however, owing to their diachronous nature, the potential for a complex history of formation, and the influence of local, non-climatic factors
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Fluorescence-detected DNA sequencing
Our research effort funded by this grant primarily focused on development of suitable fluorescent dyes for DNA sequencing studies. Prior to our efforts, the dyes being sued in commercial DNA sequencers were various versions of fluorescein dyes for the shorter wavelengths and of rhodamine dyes for the longer wavelengths. Our initial goal was to synthesize a set of four dyes that could all be excited by the 488 and 514 nm line of the argon laser lines and that have emission spectra that minimize spectral overlap. The specific result sought was higher fluorescent intensity, particularly of the longest wavelength dyes than was available using existing dyes. Another important property of the desired set of dyes was uniform ionic charge in order to have minimum interference on the electrophoretic mobility during the sequencing. During the period of this grant we prepared and characterized four types of dyes: fluorescent bifluorophores, derivatives of rhodamine dyes, derivatives of rhodol dyes and derivatives of boron dipyrromethene difluoride (BODIPY{trademark}) dyes