Fatty alcohols are of interest as a renewable feedstock to replace petroleum compounds used as fuels, in cosmetics, and in pharmaceuticals. One biological approach to the production of fatty alcohols involves the sequential action of two bacterial enzymes: (i) reduction of a fatty acyl-CoA to the corresponding fatty aldehyde catalyzed by a fatty acyl-CoA reductase, followed by (ii) reduction of the fatty aldehyde to the corresponding fatty alcohol catalyzed by a fatty aldehyde reductase. Here, we identify, purify, and characterize a novel bacterial enzyme from Marinobacter aquaeolei VT8 that catalyzes the reduction of fatty acyl-CoA by four electrons to the corresponding fatty alcohol, eliminating the need for a separate fatty aldehyde reductase. The enzyme is shown to reduce fatty acyl-CoAs ranging from C8:0 to C20:4 to the corresponding fatty alcohols, with the highest rate found for palmitoyl-CoA (C16:0). The dependence of the rate of reduction of palmitoyl-CoA on substrate concentration was cooperative, with an apparent K(m) ~ 4 μM, V(max) ~ 200 nmol NADP(+) min(-1) (mg protein)(-1), and n ~ 3. The enzyme also reduced a range of fatty aldehydes with decanal having the highest activity. The substrate cis-11-hexadecenal was reduced in a cooperative manner with an apparent K(m) of ~50 μM, V(max) of ~8 μmol NADP(+) min(-1) (mg protein)(-1), and n ~ 2.
Biodiesels (fatty
acid methyl esters) derived from oleaginous microbes
(microalgae, yeast, and bacteria) are being actively pursued as potential
renewable substitutes for petroleum diesel. Here, we report the engine
performance characteristics of biodiesel produced from a microalgae
(Chaetoceros gracilis), a yeast (Cryptococcus
curvatus), and a bacteria (Rhodococcus
opacus) in a two-cylinder diesel engine outfitted with an
eddy current brake dynamometer, comparing the fuel performance to
petroleum diesel (#2) and commercial biodiesel from soybeans. Key
physical and chemical properties, including heating value, viscosity,
density, and cetane index, for each of the microbial-derived biofuels
were found to compare favorably to those of soybean biodiesel. Likewise,
the horsepower, torque, and brake specific fuel consumption across
a range of engine speeds also compared favorably to values determined
for soybean biodiesel. Analysis of exhaust emissions (hydrocarbon,
CO, CO2, O2, and NO
x
) revealed that all biofuels produced significantly less CO and hydrocarbon
than petroleum diesel. Surprisingly, microalgae biodiesel was found
to have the lowest NO
x
output, even lower
than petroleum diesel. The results are discussed in the context of
the fatty acid composition of the fuels and the technical viability
of microbial biofuels as replacements for petroleum diesel.
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