Saccharomyces uvarum, a distinct group within Saccharomyces sensu stricto

A natural subgroup (that we refer to as Saccharomyces uvarum) was identified, within the heterogeneous species Saccharomyces bayanus. The typical electrophoretic karyotype, interfertility of hybrids between strains, distinctive sugar fermentation pattern, and uniform fermentation characteristics in must, indicated that this subgroup was not only highly homogeneous, but also clearly distinguishable from other species within the Saccharomyces sensu stricto group. Investigation of the S. bayanus type strain and other strains that have been classified as S. bayanus, confirmed the apparent lack of homogeneity and, in some cases, supported the hypothesis that they are natural hybrids. Copyright (C) 1999 Federation of European Microbiological Societies.

Rapid and efficient production of L-lactate from xylose using electrodialysis culture-associated product separation

L-Lactate was produced from xylose using electrodialysis culture (ED-C)-associated product separation. In a medium containing 50 g xylose/l, the ED-C was completed in only 32 h (i.e. less than half the time taken by the control culture, without electrodialysis). At 80 g xylose/l, the control culture was unable to consume more than 50 g xylose/1, whereas the ED-C showed increased xylose consumption and was completed by 45 h. The maximum rate of lactate production in the ED-C was higher than that in the control culture. ED-C was also carried out (at 80 g initial xylose/ l) with a supply of fresh xylose-free medium. This ED-C was completed within 30 h, which represents a reduction in fermentation time of 15 h when compared to ED-C without addition of xylose-free medium. Thus, rapid production of L-lactate was achieved by using ED-C which supplied fresh xylose-free medium.

Ethanol-induced water stress and fungal growth

Fungal growth inhibition by ethanol was compared with that caused by five other agents of water stress (at 25, 40 and 42.5°C), using Aspergillus oryzae. Ethanol, KCl, glycerol, glucose, sorbitol, and polyethylene glycol 400 were incorporated into media at concentrations corresponding to water activity (a(w)) values in the range 1 to 0.75. Generally, as temperature increased there was a decrease in the a(w) value at which optimum growth occurred. The a(w) limit for growth on KCl, glycerol, glucose, sorbitol, or polyethylene glycol 400 media was about 0.85, regardless of temperature. However, the a(w) limit for growth on ethanol media varied between 0.97 and 0.99 a(w) and was temperature-dependent. Water stress accounted for up to 31, 18 and 6% of growth inhibition by ethanol at 25, 40, and 42.5°C, respectively. For media containing ethanol, the decrease in growth rate per unit of a(w) reduction was greater as temperature increased. However, ethanol-induced water stress remained constant regardless of temperature, suggesting that other inhibitory effects of ethanol are closely temperature- dependent. Water stress may account for considerably more than 30% of growth inhibition by ethanol in cells that remain metabolically active at higher ethanol concentrations.

Ethanol-induced water stress in yeast

This review considers the effect of ethanol-induced water stress on yeast metabolism and integrity. Ethanol causes water stress by lowering water activity (a(w)) and thereby interferes with hydrogen bonding within and between hydrated cell components, ultimately disrupting enzyme and membrane strut and function. The impact of ethanol on the energetic status of water is considered in relation to cell metabolism. Even moderate ethanol concentrations (5 to 10%, w/v) cause a sufficient reduction of a(w) to have metabolic consequences. When exposed to ethanol, cells synthesize compatible solutes such as glycerol and trehalose that protect against water stress and hydrogen-bond disruption. Ethanol affects the control of gene expression by the mechanism that is normally associated with (so-called) osmotic control. Furthermore, ethanol-induced water stress has ecological implications.

Chaotropicity: a key factor in product tolerance of biofuel-producing microorganisms

Fermentation products can chaotropically disorder macromolecular systems and induce oxidative stress, thus inhibiting biofuel production. Recently, the chaotropic activities of ethanol, butanol and vanillin have been quantified (5.93, 37.4, 174kJkg(-1)m(-1) respectively). Use of low temperatures and/or stabilizing (kosmotropic) substances, and other approaches, can reduce, neutralize or circumvent product-chaotropicity. However, there may be limits to the alcohol concentrations that cells can tolerate; e.g. for ethanol tolerance in the most robust Saccharomyces cerevisiae strains, these are close to both the solubility limit (<25%, w/v ethanol) and the water-activity limit of the most xerotolerant strains (0.880). Nevertheless, knowledge-based strategies to mitigate or neutralize chaotropicity could lead to major improvements in rates of product formation and yields, and also therefore in the economics of biofuel production.

Combining Bio- and Chemo-catalysis for the Conversion of Bio-Renewable Alcohols

The use of biomass as a source of fuel is on the sharp increase. In parallel with this expansion, new chemical processes and technologies are required to improve efficiency, sustainability, and profitability.
Biocatalytic and chemocatalytic methods can be combined to affect the conversion of bio-alcohols, and convert them to valuable chemical targets in an atom efficient and environmentally benign manor. Fermentation offers a useful first step in biomass conversion, as whole cell biocatalysts can provide sustained activity when fed with crude biomass. Coupling this with homogeneous and/or heterogeneous catalysis enables the preparation of a diverse product range. The transition between biocatalytic and chemocatalytic steps can be assisted by utilising ionic liquids.
Ionic liquids have potential roles in biorefineries that generate alcohols; as an extractant, reaction medium, and catalytic reagent. Underpinning the potential of ionic liquids in this area is: 1. the ability of ionic liquids to solubilize polyols and alcohols; 2. the facility to functionalise ionic liquids and tune properties; 3. the low volatility of ionic liquids.
The FP7 project GRAIL will be highlighted; this project focusses on the utilisation of glycerol formed as a by-product in biodiesel synthesis.

Combining Bio- and Chemo-Catalysis for the Conversion of Bio-Renewable Alcohols: Homogeneous Iridium Catalysed Hydrogen Transfer Initiated Dehydration of 1,3-Propanediol to Aldehydes

Combining whole cell biocatalysis and chemocatalysis in a single reaction sequence avoids unnecessary separations, and the associated waste and energy consumption. Bacterial fermentation has been employed to convert waste glycerol from biodiesel production into 1,3-propanediol. This 1,3-propanediol can be extracted selectively from the aqueous fermentation broth using ionic liquids. 1,3-propanediol in ionic liquid solution was converted to propanal by hydrogen transfer initiated dehydration (HTID) catalysed by a Cp*IrCl2(NHC) (Cp* = pentamethylcyclopentadienyl; NHC = carbene ligand) complex. The use of an ionic liquid solvent enabled the reaction to be performed under reduced pressure, facilitating the isolation of the product, and improving the reaction selectivity. The Ir(III) catalyst in ionic liquid was found to be highly recyclable.

Magnitude differences in bioactive compounds, chemical functional groups, fatty acid profiles, nutrient degradation and digestion, molecular structure and metabolic characteristics of protein in newly developed yellow-seeded and black-seeded canola lines.

Recently, new lines of yellow-seeded (CS-Y) and black-seeded canola (CS-B) have been developed with chemical and structural alteration through modern breeding technology. However, no systematic study was found on the bioactive compounds, chemical functional groups, fatty acid profiles, inherent structure, nutrient degradation and absorption, or metabolic characteristics between the newly developed yellow- and black-seeded canola lines. This study aimed to systematically characterize chemical, structural, and nutritional features in these canola lines. The parameters accessed include bioactive compounds and antinutrition factors, chemical functional groups, detailed chemical and nutrient profiles, energy value, nutrient fractions, protein structure, degradation kinetics, intestinal digestion, true intestinal protein supply, and feed milk value. The results showed that the CS-Y line was lower (P ≤ 0.05) in neutral detergent fiber (122 vs 154 g/kg DM), acid detergent fiber (61 vs 99 g/kg DM), lignin (58 vs 77 g/kg DM), nonprotein nitrogen (56 vs 68 g/kg DM), and acid detergent insoluble protein (11 vs 35 g/kg DM) than the CS-B line. There was no difference in fatty acid profiles except C20:1 eicosenoic acid content (omega-9) which was in lower in the CS-Y line (P < 0.05) compared to the CS-B line. The glucosinolate compounds differed (P < 0.05) in terms of 4-pentenyl, phenylethyl, 3-CH3-indolyl, and 3-butenyl glucosinolates (2.9 vs 1.0 μmol/g) between the CS-Y and CS-B lines. For bioactive compounds, total polyphenols tended to be different (6.3 vs 7.2 g/kg DM), but there were no differences in erucic acid and condensed tannins with averages of 0.3 and 3.1 g/kg DM, respectively. When protein was portioned into five subfractions, significant differences were found in PA, PB1 (65 vs 79 g/kg CP), PB2, and PC fractions (10 vs 33 g/kg CP), indicating protein degradation and supply to small intestine differed between two new lines. In terms of protein structure spectral profile, there were no significant differences in functional groups of amides I and II, α helix, and β-sheet structure as well as their ratio between the two new lines, indicating no difference in protein structure makeup and conformation between the two lines. In terms of energy values, there were significant differences in total digestible nutrient (TDN; 149 vs 133 g/kg DM), metabolizable energy (ME; 58 vs 52 MJ/kg DM), and net energy for lactation (NEL; 42 vs 37 MJ/kg DM) between CS-Y and CS-B lines. For in situ rumen degradation kinetics, the two lines differed in soluble fraction (S; 284 vs 341 g/kg CP), potential degradation fraction (D; 672 vs 590 g/kg CP), and effective degraded organic matter (EDOM; 710 vs 684 g/kg OM), but no difference in degradation rate. CS-Y had higher digestibility of rumen bypass protein in the intestine than CS-B (566 vs 446 g/kg of RUP, P < 0.05). Modeling nutrient supply results showed that microbial protein synthesis (MCP; 148 vs 171 g/kg DM) and rumen protein degraded balance (DPB; 108 vs 127 g/kg DM) were lower in the CS-Y line, but there were no differences in total truly digested protein in small intestine (DVE) and feed milk value (FMV) between the two lines. In conclusion, the new yellow line had different nutritional, chemical, and structural features compared to the black line. CS-Y provided better nutrient utilization and availability.

Organophosphonates revealed: new insights into the microbial metabolism of ancient molecules.

Organophosphonates are ancient molecules that contain the chemically stable C–P bond, which is considered a relic of the reducing atmosphere on primitive earth. Synthetic phosphonates now have a wide range of applications in the agricultural, chemical and pharmaceutical industries. However, the existence of C–P compounds as contemporary biogenic molecules was not discovered until 1959, with the identification of 2-aminoethylphosphonic acid in rumen protozoa. Here, we review advances in our understanding of the biochemistry and genetics of microbial phosphonate metabolism, and discuss the role of these compounds and of the organisms engaged in their turnover within the P cycle.