Effects of surfactant mixtures, including Corexit 9527, on bacterial oxidation of acetate and alkanes in crude oil

Mixtures of nonionic and anionic surfactants, including Corexit 9527, were tested to determine their effects on bacterial oxidation of acetate and alk anes in crude oil by cells pregrown on these substrates, Corexit 9527 inhib ited oxidation of the alkanes in crude oil by Acinetobacter calcoaceticus A TCC 31012, while Span 80, a Corexit 9527 constituent, markedly increased th e oil oxidation rate. Another Corexit 9527 constituent, the negatively char ged dioctyl sulfosuccinate (AOT), strongly reduced the oxidation rate. The combination of Span 80 and AOT increased the rate, but not as much as Span 80 alone increased it, which tentatively explained the negative effect of C orexit 9527, The results of acetate uptake and oxidation experiments indica ted that the nonionic surfactants interacted with the acetate uptake system while the anionic surfactant interacted with the oxidation system of the b acteria. The overall effect of Corexit 9527 on alkane oxidation by A. calco aceticus ATCC 31012 thus seems to be the sum of the independent effects of the individual surfactants in the surfactant mixture. When Rhodococcus sp, strain 094 was used, the alkane oxidation rate decreased to almost zero in the presence of a mixture of Tergitol 15-S-7 and AOT even though the Tergit ol 15-S-7 surfactant increased the alkane oxidation rate and AOT did not af fect it. This indicated that there was synergism between the two surfactant s rather than an additive effect like that observed for ii. calcoaceticus A TCC 31012.