Biotechnology and oleochemicals: Changing patterns

n-Alkane chain length alters Dietzia sp. strain DQ12-45-1b biosurfactant production and cell surface activity

Upon growth on n-hexadecane (C(16)), n-tetracosane (C(24)), and n-hexatriacontane (C(36)), Dietzia sp. strain DQ12-45-1b could produce different glycolipids, phospholipids, and lipopeptides. Interestingly, cultivation with C(36) increased cell surface hydrophobic activity, which attenuated the negative effect of the decline of the emulsification activity. These results suggest that the mechanisms of biosurfactant production and cell surface hydrophobicity are dependent upon the chain lengths of the n-alkanes used as carbon sources.

Long-chain aldehyde dehydrogenase that participates in n-alkane utilization and wax ester synthesis in Acinetobacter sp. strain M-1

A long-chain aldehyde dehydrogenase, Ald1, was found in a soluble fraction of Acinetobacter sp. strain M-1 cells grown on n-hexadecane as a sole carbon source. The gene (ald1) was cloned from the chromosomal DNA of the bacterium. The open reading frame of ald1 was 1,512 bp long, corresponding to a protein of 503 amino acid residues (molecular mass, 55,496 Da), and the deduced amino acid sequence showed high similarity to those of various aldehyde dehydrogenases. The ald1 gene was stably expressed in Escherichia coli, and the gene product (recombinant Ald1 [rAld1]) was purified to apparent homogeneity by gel electrophoresis. rAld1 showed enzyme activity toward n-alkanals (C(4) to C(14)), with a preference for longer carbon chains within the tested range; the highest activity was obtained with tetradecanal. The ald1 gene was disrupted by homologous recombination on the Acinetobacter genome. Although the ald1 disruptant (ald1Delta) strain still had the ability to grow on n-hexadecane to some extent, its aldehyde dehydrogenase activity toward n-tetradecanal was reduced to half the level of the wild-type strain. Under nitrogen-limiting conditions, the accumulation of intracellular wax esters in the ald1Delta strain became much lower than that in the wild-type strain. These and other results imply that a soluble long-chain aldehyde dehydrogenase indeed plays important roles both in growth on n-alkane and in wax ester formation in Acinetobacter sp. strain M-1.

Growth of three fungi on poultry fat or beef tallow

Aspergillus niger, Geotrichum candidum and Mucor miehei, when grown on a medium containing beef tallow or poultry fat for 5 days at 28°C, in Roux bottles, shake-flasks or fermenters, synthesized from 0.4 to 3.2 g lipids/I. The degree of fat utilization varied from 15 to 70%. The type of fat in the medium, the species of fungi and its cultivation method all influenced the fatty acid composition of fats remaining in the medium, as well as the intracellular lipids of the fungi.

Purification and characterization of Pseudomonas fluorescens SIK W1 lipase expressed in Escherichia coli

Pseudomonas fluorescens SIK W1 lipase was expressed as a form of inclusion bodies in Escherichia coli, which was equivalent to 46% of total cell protein. The inclusion bodies isolated from other cell components were solubilized in the buffer containing 8 M urea and then refolded by diluting urea. The lipase with active conformation was purified by hydrophobic interaction chromatography, gel filtration, anion-exchange chromatography and hydroxyapatite chromatography from the refolded sample. By these purification steps, a single band for active lipase was detected on non-reducing SDS-PAGE and 10-fold purification was attained on the basis of specific activity. Specific activity of the purified lipase toward olive oil emulsion was found to be 7395 units per mg protein. The optimum pH and temperature of the lipase were pH 8.5 and 45-55 degrees C, respectively. The lipase showed higher lipolytic activity toward tricaproin (C6) and tricaprylin (C8) among the triacylglycerols examined and preferentially hydrolyzed ester bond of 1- and 3-position of triolein. Lipase activity was greatly increased by approx. 6-fold and stability for pH was shifted to alkaline pH by Ca2+ ion. The lipase was inhibited by Hg2+, Ag2+, p-chloromercuribenzoate, diethylpyrocarbonate and sodium dodecyl sulfate.

Recent advances in the purification, characterization and structure determination of lipases

Recently, lipases have been purified from mammalian, bacterial, fungal and plant sources by different methodologies. Purified lipases subsequently have been characterized for molecular size, metal binding capabilities, glycoside and phosphorus contents, and substrate specificities. Primary structures of several lipases have been determined either from amino acid or nucleic acid sequences. Lipases sequenced to date share sequence homologies including a significant region, Gly-X-Ser-X-Gly, that is conserved in all. The Ser residue is suspected to be essential for binding to lipid substrates.