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Microbial oxidation of n-alkane hydrocarbons Liu, Dickson Lee Shen

Abstract

A four-part investigation was described in which first, the use of thiolignin and lignosulfonate to remove a factor involved in growth limitation in hydrocarbon fermentation was investigated; secondly, the performance of the Cyelone-fermenter in hydrocarbon fermentation was evaluated; thirdly, continuous hydrocarbon fermentation with reference to hydrocarbon, nitrogen, thiolignin and dilution rate was studied; and fourthly, the mechanism of n-decane oxidation was studied manometrically and gas chromatographically. The addition of polymerized lignosulfonate and thiolignin into the hydrocarbon fermentation media greatly, increased the fermentation rate and the yield of biomass. Lignin itself did not appear to be decomposed during the fermentation. Resting cell studies of Pseudomonas desmolytica S(11) indicated that the oxygen consumption increased with the decreasing n-alkane carbon number and did not parallel the production of total biomass. The greatest biomass occurred using n-undecane and decreased sharply with lower and higher n-alkanes. The individual n-alkanes in kerosene were not degraded uniformly, the lower ones were used preferentially. Thiolignin not only increased the rate of utilization of these lower n-alkanes but also extended microbial acceptability to the higher n-alkanes. Gas chromatographic analyses revealed that five monocarboxylic fatty acids corresponding to C(8), C(9), C(10, C(11), and C(12) were present in the fermentation fluid. The Cyclone-fermenter was found to be very suitable for hydrocarbon fermentation. The hydrocarbon, kerosene, was fermented with a pure bacterial culture in a continuous process for 250 hours without any noticeable change in the culture behavior. Moreover, the addition of various culture medium ingredients could be optimized to produce maximum cell yield or maximum acid production. Manometric and gas chromatographic studies revealed that cell-free extracts of 2(11) oxidized n-decane to n-decanol and n-decanoic acid, whereas the partially purified hydrocarbon-oxidizing enzyme only oxidized n-decane to decanol. The n-decane-oxidizing enzyme could be precipitated by 30% (NH4)2 SO4 and had a narrow optimal pH around 7.0. The enzyme also required a dialyzed, heat stable 60% (NH4)2 SO4 supernatant fraction and NAD for maximum enzyme activity. Ferrous, manganous and calcium ions did not stimulate the enzyme activity. It seemed that the enzymatic attack on n-decane occurred primarily at the terminal carbon atom and this was manifested by the fact that n-decanol, n-decanal and n-decanoic acid supported good growth for S(11).

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