Effects of carbon dioxide on mitochondrial enzymes from Ricinus

The glutamate decarboxylase acid resistance mechanism affects survival of Listeria monocytogenes LO28 in modified atmosphere-packaged foods

AIMS

The contribution of the glutamate decarboxylase (GAD) acid resistance system to survival and growth of Listeria monocytogenes LO28 in modified atmosphere-packaged foods was examined.

METHODS AND RESULTS

The survival and growth of the wild-type LO28 and four GAD deletion mutants (DeltagadA, DeltagadB, DeltagadC, DeltagadAB) in packaged foods (minced beef, lettuce, dry coleslaw mix) during storage at 4, 8 and 15 degrees C were studied. Survival and growth patterns varied with strain, product type, gas atmosphere and storage temperature. In minced beef, the wild-type LO28 survived better (P < 0.05) than the GAD mutant strains at 8 and 15 degrees C. In both packaged vegetables at all storage temperatures, the wild-type strain survived better (P < 0.05) than the double mutant DeltagadAB. The requirement for the individual gad genes varied depending on the packaged food. In the case of lettuce, gadA played the most important role, while the gadB and gadC genes played the greatest role in packaged coleslaw (at 15 degrees C).

CONCLUSIONS

This work demonstrates that elements of the GAD system play significant roles in survival of L. monocytogenes LO28 during storage in modified atmosphere-packaged foods.

SIGNIFICANCE AND IMPACT OF THE STUDY

A better understanding of how L. monocytogenes behaves in modified atmosphere-packaged foods, and how it responds to elevated carbon dioxide atmospheres.

Contrasting responses by respiration to elevated CO2 in intact tissue and isolated mitochondria

The question of whether elevated concentrations of CO₂ directly inhibit mitochondrial respiration in plants has received considerable attention. Although there is a growing consensus that elevated [CO₂] rarely inhibits respiration of intact tissues, past studies have reported that elevated [CO₂] does impact on O₂ uptake in isolated mitochondria; what remains unclear, however, is the site(s) where elevated [CO₂] impacts on mitochondrial electron transport (ETC). Here we investigated direct effects of [CO₂] on respiratory activity of ETC enzymes, intact mitochondria and whole tissues using potato tubers (Solanum tuberosum L. cv. Desiree). Plots of O₂ uptake against the redox poise of the ubiquinone (UQ) pool in isolated mitochondria were used to determine whether elevated [CO₂] inhibits UQ-reducing and UQ-oxidising pathways differentially. Our results show that mitochondrial respiration was more inhibited via [CO₂]/[HCO₃^-] effects on cytochrome c oxidase (COX) than on succinate dehydrogenase, with [HCO₃^-] rather than [CO₂] inhibiting COX. However, the inhibitory effects at the mitochondrial level did not translate into inhibitory effects at the tissue level. Alternative oxidase (AOX) activity is normally absent in young potato tubers, as was the case in the present study. Thus, the lack of CO₂-mediated inhibition at the tissue level was not the result of increases in AOX activity masking the effects of CO₂ elsewhere in the respiratory system. We discuss whether the direct impact of elevated [CO₂] on respiration is dependent on the rate of metabolic activity and flux control coefficients in individual tissues.

CO2- and anaerobiosis-induced changes in physiology and gene expression of different Listeria monocytogenes strains

Although carbon dioxide (CO(2)) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high CO(2) concentrations at refrigeration temperatures. We examined the listerial responses of different strains to growth in air, 100% N(2), and 100% CO(2). The CO(2)-induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to CO(2) as to other anaerobic, slightly acidic environments (100% N(2), pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO(2) and N(2) at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO(2)-containing atmospheres. Together, our findings demonstrate that the CO(2)-response is a partly strain-dependent complex mechanism. The possible links between the CO(2)-dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed.

Effect of a Brief CO(2) Exposure on Ethylene Production

Ethylene production and respiration by Granny Smith apples were inhibited by treatment with 20% CO(2) for 2 hours. A similar effect was observed in tissue slices when treated at either 0 or 25 degrees C.The inhibition continued even after an extended aeration period. There is also an inhibition of ethylene emission in tissue slices incubated with exogenous 1-aminocyclopropane-1-carboxylic acid (ACC).In general, CO(2) treatment increased the ACC content of the tissue. These observations are consistent with the idea the action of CO(2) is directed toward the enzyme system responsible for the conversion of ACC into ethylene.

Effects of carbon dioxide on activity of apple mitochondria

Effects of CO(2) on mitochondrial activity of apple (Malus pumila Mill. var. Richared Delicious) were studied in two ways. Immediate effects were determined by imposing 3 to 18% CO(2)-bicarbonate mixtures on isolated apple mitochondria, and long term effects were determined by extracting mitochondria from apples that had been stored for intervals in atmospheres containing 6 or 12% CO(2) plus 3% O(2). The CO(2)-bicarbonate systems had immediate and broad effects on mitochondrial oxidations: 18% CO(2) stimulated malate oxidation about 10%; suppressed alpha-ketoglutarate, citrate, and NADH oxidations about 10%; and suppressed fumarate, pyruvate, and succinate oxidations about 32%. The effects of lower CO(2) concentrations varied with substrates. Mitochondria isolated from fruit stored in 6 or 12% CO(2) possessed a reduced capacity to oxidize added succinate or NADH, but retained a marked sensitivity to CO(2)-bicarbonate mixtures. Respiratory control in these mitochondria was somewhat reduced, but CO(2) had not acted as a strong uncoupling agent.

Effects of air flow rate, storage temperature, and harvest maturity on respiration and ripening of tomato fruits

The interactive effects of aeration rate, storage temperature, harvest maturity, and storage duration on respiration and ripening of tomato fruits (Lycopersicum esculentum var. Roma) were studied. Slow aeration rate strongly reduced the climacteric but did not affect ripening. Low temperature slowed ripening and reduced respiratory rates, but low temperature did not delay attainment of the climacteric maxima. The effect of air flow rate on the content of CO(2) in the fruits' internal atmospheres was investigated. The possibility that CO(2) is not the primary cause of respiratory inhibition under slow air flow rate is discussed.

Gas exchange of algae. 3. Relation between the concentration of carbon dioxide in the nutrient medium and the oxygen production of Chlorella pyrenoidosa

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.

Effects of carbon dioxide-bicarbonate mixtures on oxidative phosphorylation by cauliflower mitochondria

1. Carbon dioxide-bicarbonate mixtures markedly inhibited oxidation and phosphorylation rates of mitochondria prepared from cauliflower. Inhibition occurred with succinate, malate, citrate, isocitrate and NADH as substrates. 2. Indophenol-reductase systems with malate, succinate, isocitrate and NADH as substrates were inhibited by 5% and 15% carbon dioxide. Cytochrome c oxidase was not inhibited by 15% carbon dioxide.