The effects of carbon dioxide on growth, fatty acid composition and tricarboxylic acid cycle of some microorganisms isolated from Gulf of Mexico black drum (Pogonias cromis)

Typescript (photocopy).Potential mechanisms for the inhibitory properties of carbon dioxide (CO(,2)) on common type microorganisms isolated from fish were investigated. The organisms used were initially isolated from black drum (Pogonias cromis) harvested in the Gulf of Mexico. Aerobic plate counts (APC) at the time of harvest averaged 5 x 10('2)/cm('2). During storage on ice, bacterial numbers increased approximately 1 log cycle for every 3 days averaging 2.9 x 10('5)/cm('2) at the end of the storage period. At day 0 and day 3, the microflora was comprised predominantly of gram-positive organisms, mainly Micrococcus and Streptococcus spp. After 6 and 9 days of storage, the percentage of gram-positive bacteria declined dramatically. The main bacterial types isolated were P. fluorescens and a Moraxella sp. A number of microorganisms belonging to various taxonomical groups were selected for sensitivity studies to CO(,2) in atmospheres containing 25 to 100% CO(,2). Growth rates of the organisms at 4 and 25 C were determined by measuring the rate of increase in diameter of colonies spotted on prepoured trypticase soy agar (TSA) plates. A significant decrease in the growth rates of all bacteria was caused by CO(,2), and its effects were greatly enhanced by low temperatures. However, no clearcut lines of CO(,2)-susceptibility, according to microbial taxonomy, could be established. The effects of CO(,2) on the cellular fatty acid composition of a Moraxella sp. and a Vibrio sp., and of P. fluorescens were also determined. A trend showing an increased degree of unsaturation was observed for all organisms growing in CO(,2)-enriched environments. The overall chain length of the major fatty acids showed a decrease in the Moraxella sp. and the Vibrio sp., whereas a small increase occurred in P. fluorescens. Exposure of bacterial cells to CO(,2) also altered the pool of tricarboxylic acid (TCA) cycle intermediates in all three microorganisms. Accumulation of metabolic products at several intermediate steps in the TCA cycle indicated that inhibition of several specific enzyme systems did take place. Since isocitrate dehydrogenase (NADP) seemed especially sensitive to CO(,2), this enzyme was selected for further studies. When assayed in 9.0 mM CO(,2), a 7% drop in activity was observed. The inhibition was found to be uncompetitive with respect with CO(,2)