Enzymatic Preparation of Mono- and Di-Stearin by Glycerolysis of Ethyl Stearate and Direct Esterification of Glycerol in the Presence of a Lipase from Candida Antarctica (Novozym 435)

Mixtures of 1(3)-monostearin and distearin were prepared by direct esterification of glycerol with stearic acid or transesterification using ethyl stearate as acyl donor in the presence of Candida antarctica lipase (Novozym 435) using a variety of solvents of differing polarity. In all cases, the transesterification resulted in higher product yields. In n-heptane as reaction medium the addition of water (3%) was essential for high product yields, with mono- and distearin being produced in almost equal amounts. Using more polar solvents as reaction media, such as acetonitrile or acetone, again the highest yields were obtained in the transesterification mode; employing these solvents the reactions were much more selective towards the formation of monostearin.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Staphylococcal growth and enterotoxins (A—D) and thermonuclease synthesis in the presence of dehydrated garlic

E. GONZÁLEZ-FANDOS, M.L. GARCÍA-LÓPEZ, M.L. SIERRA AND A. OTERO. 1994. The inhibition of Staphylococcus aureus growth and enterotoxin and thermonuclease production by various concentrations of garlic ( Allium sativum ) was studied in BHI broth. The growth of Staph. aureus was inhibited by dehydrated garlic at levels of 1.5% (w/v) and over. Enterotoxins A, B and C₁ were only detectable in broth containing < 1% of garlic while enterotoxin D was produced at a level of 2%. Garlic also inhibited thermonuclease (TNAse) production, complete inhibition being observed at levels ≥ 1.5%. TNAse was not always detected when enterotoxin was present.     

Behaviour of Candida utilis during growth in relation to Mg2+ and K+ concentration in sugar cane molasses

Magnesium and potassium ions are present in sugar cane molasses in a concentration of about 0.3% and 2.5%, respectively, which is high enough to support biomass production from Candida utilis. Culture broth with 40 g/l of total reducing substances supplemented by the addition of 1 ppm of Mg²⁺ leads to a higher yield (Y x/s) in batch fermentation experiments. The subsequent addition of Mg²⁺ up to 10 ppm decreases the yield coefficient from 0.53 to 0.42 without affecting the growth rate. Fermentation media supplemented with 1 to 10 ppm of K⁺ decreased both the yield coefficient and the specific growth rate. A Mg/K ratio of about 0.1 seems to be optimal for yeast biomass propagation.     

Tris not only controls the pH in microalgal cultures,but also feeds bacteria

Tris (Tris(hydroxymethyl)amino methane), a compound often used as a buffer in microalgal culture media, sustains active bacterial growth in non-axenic microalgal cultures when sodium phosphate is present. The low pH levels caused by bacterial growth and probably the depletion of phosphorus in the medium caused the collapse ofPhaeodactylum tricornutum cultures resulting in a reduction of microalgal growth from 32 x 10⁶ to 1.1 x 10⁶ cells ml^–1. This emphasizes the need for care when interpreting the results of non-axenic microalgae cultures in which Tris or other organic buffer is added.     

Use of agricultural surpluses for production of biomass by marine microalgae

The marine microalga Phaeodactylum tricornutum was cultivated in semi-continuous culture under mixotrophic conditions with the soluble fractions of potato, rye and wheat flours that had been naturally fermented, at 2% or 4% (w/v). The rye flour produced the highest microalgal cellular density of 90×10⁶ cells.ml^-1 when supplemented with NaNO₃ and NaH₂PO₄. The autotrophic control only gave 57×10⁶ cells.ml^-1. The value of agricultural surpluses, such as rye flour, can therefore be increased by its use in the production of valuable, microalgal biomass which is rich in protein, pigments and fatty acids.     

Mixotrophic productivity of the marine diatom Phaeodactylum tricornutum cultured with soluble fractions of rye,wheat and potato

The marine microalga Phaeodactylum tricornutum was cultured semi-continuously with the soluble fractions of wheat, rye and boiled potato flours. Fifteen percent of the culture volume was renewed every 3 d. The cell productivities were 0.9×109 cells/l/d, 1.1×109 cells/l/d and 2.6×109 cells/l/d for wheat, rye and potato respectively. The productivity of the autotrophic control was 1.0×109 cell/l/d. When a soluble fraction of raw potato was added, the productivity was enhanced to 4.1×109 cells/l/d, 2.4 times higher than the autotrophic culture. The high productivity of P. tricornutum with the soluble fractions of Solanum tuberosum suggests its usefulness as a source of nutrients for the production of microalgal biomass.     

Predisposing factors in systemic and central nervous system candidiasis: Histopathological and cultural observations in the rat

Four atypical isolates of Microsporum canis, three from humans and one from a cat, were obtained from North-West London. These and a further human isolate were compared with each other and with a typical isolate of the fungus. Immediately after isolation the atypical isolates were very labile, but were stabilised after a few subcultures from selected sectors. The stable forms differed from each other, but all had a tendency to brown rather than yellow pigmentation, to feathery submerged mycelium and to abnormal macroconidia. The macroscopic appearance and texture of the colonies depended on the density, orientation and branching pattern of the submerged mycelium.In recent years similar brown, feathery forms of M. canis have been reported from monkeys but not from cats. It is suggested that all such isolates may be culturally stable forms of a very unstable strain, probably feline in origin, which has yet to be described.