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Saccharomyces cerevisiae wine-producing yeast cultures grown under model winemaking conditions could be induced to liberate hydrogen sulfide (H 2 S) by starvation for assimilable nitrogen. The amount of H 2 S produced was dependent on the yeast strain, the sulfur precursor compound, the culture growth rate, and the activity of the sulfite reductase enzyme (EC 1.8.1.2) immediately before nitrogen depletion. Increased H 2 S formation relative to its utilization by metabolism was not a consequence of a de novo synthesis of sulfite reductase. The greatest amount of H 2 S was produced when nitrogen became depleted during the exponential phase of growth or during growth on amino acids capable of supporting short doubling times. Both sulfate and sulfite were able to act as substrates for the generation of H 2 S in the absence of assimilable nitrogen; however, sulfate reduction was tightly regulated, leading to limited H 2 S liberation, whereas sulfite reduction appeared to be uncontrolled. In addition to ammonium, most amino acids were able to suppress the liberation of excess H 2 S when added as sole sources of nitrogen, particularly for one of the strains studied. Cysteine was the most notable exception, inducing the liberation of H 2 S at levels exceeding that of the nitrogen-depleted control. Threonine and proline also proved to be poor substitutes for ammonium. These data suggest that any compound that can efficiently generate sulfide-binding nitrogenous precursors of organic sulfur compounds will prevent the liberation of excess H 2 S.

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The yeast Lachancea thermotolerans (previously Kluyveromyces thermotolerans) is a species of large, yet underexplored, oenological potential. This study delivers comprehensive oenological phenomes of 94 L. thermotolerans strains obtained from diverse ecological niches worldwide, classified in nine genetic groups based on their pre-determined microsatellite genotypes. The strains and the genetic groups were compared for their alcoholic fermentation performance, production of primary and secondary metabolites and pH modulation in Chardonnay grape juice fermentations. The common oenological features of L. thermotolerans strains were their glucophilic character, relatively extensive fermentation ability, low production of acetic acid and the formation of lactic acid, which significantly affected the pH of the wines. An untargeted analysis of volatile compounds, used for the first time in a population-scale phenotyping of a non-Saccharomyces yeast, revealed that 58 out of 90 volatiles were affected at an L. thermotolerans strain level. Besides the remarkable extent of intra-specific diversity, our results confirmed the distinct phenotypic performance of L. thermotolerans genetic groups. Together, these observations provide further support for the occurrence of domestication events and allopatric differentiation in L. thermotolerans population.

Successful and timely completion by Dissertation Research (DR) students (i.e. research Masters and PhD) is increasingly important for students, supervisors, the university, and funding bodies alike. Previous studies highlight the importance of contributing factors, which can be classified according to their relating to the student, the supervisory arrangement, or the research infrastructure. However, the relative importance of specific factors for individual students can vary markedly across studies. In recognition of this fact, a survey of DR student completion rates and candidature duration within an Australian Faculty of Sciences (i.e. the author's home institution and broad field of research activity) was conducted. Available information was extracted for a 10-year window (1996-2006) from faculty-level and university-level databases and included data relating to demographics, field of study, attendance mode, scholarships held, and duration of candidature for up to 1688 students. The results suggest an attrition rate of 33% with shorter completion times being seen within the School of Chemistry & Physics and among male and/or international students with scholarships. Possible predictors of HRD student success are considered, thereby beginning to provide a framework within which to develop practices to increase retention and completion rates in other areas of the faculty.

We report the cloning and characterization of EstB28, the first esterase to be so characterized from the wine-associated lactic acid bacterium, Oenococcus oeni. The published sequence for O. oeni strain PSU-1 was used to identify putative esterase genes and design PCR primers in order to amplify the corresponding region from strain Ooeni28, an isolate intended for inoculation of wines. In this way a 912-bp open reading frame (ORF) encoding a putative esterase of 34.5 kDa was obtained. The amino acid sequence indicated that EstB28 is a member of family IV of lipolytic enzymes and contains the GDSAG motif common to other lactic acid bacteria. This ORF was cloned into Escherichia coli using an appropriate expression system, and the recombinant esterase was purified. Characterization of EstB28 revealed that the optimum temperature, pH, and ethanol concentration were 40°C, pH 5.0, and 28% (vol/vol), respectively. EstB28 also retained marked activity under conditions relevant to winemaking (10 to 20°C, pH 3.5, 14% [vol/vol] ethanol). Kinetic constants were determined for EstB28 with p-nitrophenyl (pNP)-linked substrates ranging in chain length from C 2 to C 18 . EstB28 exhibited greatest specificity for C 2 to C 4 pNP-linked substrates.

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