Effect of Various Gas Atmospheres on Destruction of Microorganisms in Dry Heat

The heat resistance of dry bacterial spores was tested in various gases at temperatures ranging from 121.1 to 160 C (250 to 320 F). Spores of Clostridium sporogenes (PA 3679) were heated in air, carbon dioxide, and helium; spores of Bacillus subtilis 5230 were heated in these gases and also in oxygen and in nitrogen. The surrounding gas influenced the heat resistance, but the differences among gases were small. D values were about 7 min at 148.9 C (300 F); z values were about 18.3 C (33 F) for B. subtilis, and about 21.7 C (39 F) for C. sporogenes. The resistance of B. subtilis in carbon dioxide was about the same as in air, but lower than in all other gases; resistance in helium and nitrogen was about the same, and was higher than in all other gases. C. sporogenes had the least resistance in air; the resistance was about the same in carbon dioxide and helium. For B. subtilis, the gases in order of increasing heat resistance were carbon dioxide, air, oxygen, helium, and nitrogen, and for C. sporogenes, air, carbon dioxide, and helium. Neither oxygen content nor molecular weight of the gas appeared to have a marked influence on dry-heat resistance of the spores, whereas the more inert gases seemed to yield larger D values.     

Anaerobic mineralization of cholesterol by a novel type of denitrifying bacterium

A novel denitrifying bacterium, strain 72Chol, was enriched and isolated under strictly anoxic conditions on cholesterol as sole electron donor and carbon source. Strain 72Chol grew on cholesterol with oxygen or nitrate as electron acceptor. Strictly anaerobic growth in the absence of oxygen was demonstrated using chemically reduced culture media. During anaerobic growth, nitrate was initially reduced to nitrite. At low nitrate concentrations, nitrite was further reduced to nitrogen gas. Ammonia was assimilated. The degradation balance measured in cholesterol-limited cultures and the amounts of carbon dioxide, nitrite, and nitrogen gas formed during the microbial process indicated a complete oxidation of cholesterol to carbon dioxide. A phylogenetic comparison based on total 16S rDNA sequence analysis indicated that the isolated micro-organism, strain 72Chol, belongs to the β2-subgroup in the Proteobacteria and is related to Rhodocyclus, Thauera, and Azoarcus species. Received: 16 July 1996 / Accepted: 5 December 1996     

Gas Exchange of Algae: II. Effects of Oxygen, Helium, and Argon on the Photosynthesis of Chlorella pyrenoidosa

Changes in the oxygen partial pressure of air over the range of 8 to 258 mm of Hg did not adversely affect the photosynthetic capacity of Chlorella pyrenoidosa. Gas exchange and growth measurements remained constant for 3-week periods and were similar to air controls (oxygen pressure of 160 mm of Hg). Oxygen partial pressures of 532 and 745 mm of Hg had an adverse effect on algal metabolism. Carbon dioxide consumption was 24% lower in the gas mixture containing oxygen at a pressure 532 mm of Hg than in the air control, and the growth rate was slightly reduced. Oxygen at a partial pressure of 745 mm of Hg decreased the photosynthetic rate 39% and the growth rate 37% over the corresponding rates in air. The lowered metabolic rates remained constant during 14 days of measurements, and the effect was reversible after this time. Substitution of helium or argon for the nitrogen in air had no effect on oxygen production, carbon dioxide consumption, or growth rate for 3-week periods. All measurements were made at a total pressure of 760 mm of Hg, and all gas mixtures were enriched with 2% carbon dioxide. Thus, the physiological functioning and reliability of a photosynthetic gas exchanger should not be adversely affected by: (i) oxygen partial pressures ranging from 8 to 258 mm of Hg; (ii) the use of pure oxygen at reduced total pressure (155 to 258 mm of Hg) unless pressure per se affects photosynthesis, or (iii) the inclusion of helium or argon in the gas environment (up to a partial pressure of 595 mm of Hg).     

Nitrate reduction and assimilation in Chlorella

1. Nitrate reduction and assimilation have been studied in Chlorella pyrenoidosa under growth conditions by observing effects on the CO(2)/O(2) gas exchange quotient. 2. During assimilation of glucose in the dark, nitrate reduction is noted as an increase in the R.Q. to about 1.6 caused by an increased rate of carbon dioxide production. 3. During photosynthesis at low light intensity nitrate reduction is evidenced by a reduction in the CO(2)O(2) quotient to about 0.7 caused by a decreased rate of carbon dioxide uptake. 4. Chlorella will assimilate nitrogen from either nitrate or ammonia. When both sources are supplied, only ammonia is utilized and no nitrate reduction occurs. It is inferred that under the usual conditions of growth nitrate is reduced only at a rate required for subsequent cellular syntheses. The effect of nitrate reduction on the CO(2)O(2) quotient therefore provides a measure of the relative rate of nitrogen assimilation. 5. Over-all photosynthetic metabolism may be described from elementary analysis of the cells since excretory products are negligible. The gas exchange predicted in this way is in good agreement with the observed CO(2)/O(2) quotients.     

Nitrogen Cycling and Nitric Oxide Emissions in Oil-Impacted Prairie Soils

A remote site in the Tallgrass Prairie Preserve of Oklahoma (The Nature Conservancy) was contaminated with crude oil from a pipeline break and is being bioremediated using landfarming techniques. Landfarming is designed to stimulate microbial-based catabolism of petroleum through combined dilution/mixing and fertilization-based effects. To evaluate nitrogen-based effects during remediation, the site was sectioned and treated with urea, ammonium sulfate, or ammonium nitrate. Samples were obtained from prairie soil without chemical nitrogen addition and with or without hydrocarbon contamination. Nitrogen cycling dynamics were followed by measuring ammonium, nitrite, nitrate, and volatile nitric oxide (NO_x) levels. Nitrifying and denitrifying bacterial numbers were estimated and compared to soil oxygen, carbon dioxide, and methane levels as well as to overall total petroleum hydrocarbon (TPH) reduction. For a prairie ecosystem of this type, a high level of fertilization, particularly with nitrogen, can have ecological effects almost as profound as the petroleum contamination itself. Fertilization of the oil-contaminated soil with the reduced and/or oxidized forms of nitrogen quickly resulted in elevated steady-state levels of both ammonium and nitrate, and exceptionally high levels of NO_x released from soil. Although nitrogen fertilization increased microbial nitrogen metabolism and nitrogen cycling, it had minimal effects on the overall remediation efficiency.     

Factors controlling anaerobic ammonium oxidation with nitrite in marine sediments

Factors controlling the anaerobic oxidation of ammonium with nitrate and nitrite were explored in a marine sediment from the Skagerrak in the Baltic-North Sea transition. In anoxic incubations with the addition of nitrite, approximately 65% of the nitrogen gas formation was due to anaerobic ammonium oxidation with nitrite, with the remainder being produced by denitrification. Anaerobic ammonium oxidation with nitrite exhibited a biological temperature response, with a rate optimum at 15 degrees C and a maximum temperature of 37 degrees C. The biological nature of the process and a 1:1 stoichiometry for the reaction between nitrite and ammonium indicated that the transformations might be attributed to the anammox process. Attempts to find other anaerobic ammonium-oxidizing processes in this sediment failed. The apparent K(m) of nitrite consumption was less than 3 microM, and the relative importance of ammonium oxidation with nitrite and denitrification for the production of nitrogen gas was independent of nitrite concentration. Thus, the quantitative importance of ammonium oxidation with nitrite in the jar incubations at elevated nitrite concentrations probably represents the in situ situation. With the addition of nitrate, the production of nitrite from nitrate was four times faster than its consumption and therefore did not limit the rate of ammonium oxidation. Accordingly, the rate of this process was the same whether nitrate or nitrite was added as electron acceptor. The addition of organic matter did not stimulate denitrification, possibly because it was outcompeted by manganese reduction or because transport limitation was removed due to homogenization of the sediment.     

Tamarind seed powder and palm kernel cake: two novel agro residues for the production of tannase under solid state fermentation by Aspergillus niger ATCC 16620

Palm kernel cake (PKC), the residue obtained after extraction of palm oil from oil palm seeds and tamarind seed powder (TSP) obtained after removing the fruit pulp from tamarind fruit pod were tested for the production of tannase under solid-state fermentation (SSF) using Aspergillus niger ATCC 16620. The fungal strain was grown on the substrates without any pretreatment. In PKC medium, a maximum enzyme yield of 13.03 IU/g dry substrate (gds) was obtained when SSF was carried out at 30 degrees C, 53.5% initial substrate moisture, 33 x 10(9) spores/5 g substrate inoculum size and 5% tannic acid as additional carbon source after 96 h of fermentation. In TSP medium, maximum tannase yield of 6.44 IU/gds was obtained at 30 degrees C, 65.75% initial substrate moisture, 11 x 10(9) spores/5 g substrate inoculum, 1% glycerol as additional carbon source and 1% potassium nitrate as additional nitrogen source after 120 h of fermentation. Results from the study are promising for the economic utilization and value addition of these important agro residues, which are abundantly available in many tropical and subtropical countries.     

Acetylene reduction and respiration of bacteroids isolated from French-beans receiving nitrate

The competition between combined nitrogen and nitrogen fixation in legumes was studied after a 24 h exposure of nodulated French-beans to nitrate. Acetylene reduction by bacteroids was significantly inhibited and even nitrogenase extracted from nitrate-treated plant nodules showed reduced activity. Sensitivity to nitrate was directly related to nodule age and also increased with increasing oxygen tensions in the bacteroid incubations with or without a gas phase; it was particularly marked when glucose was used in place of succinate as energy-yielding substrate. Bacteroid respiration was also depressed by nitrate-treatment of the plants, leading to diminished acetylene reduction and this effect increased with increasing oxygen concentrations. Added oxyleghemoglobin partly restored oxygen consumption and acetylene reduction by bacteroid suspensions.     

Factors Controlling Anaerobic Ammonium Oxidation with Nitrite in Marine Sediments

Factors controlling the anaerobic oxidation of ammonium with nitrate and nitrite were explored in a marine sediment from the Skagerrak in the Baltic-North Sea transition. In anoxic incubations with the addition of nitrite, approximately 65% of the nitrogen gas formation was due to anaerobic ammonium oxidation with nitrite, with the remainder being produced by denitrification. Anaerobic ammonium oxidation with nitrite exhibited a biological temperature response, with a rate optimum at 15°C and a maximum temperature of 37°C. The biological nature of the process and a 1:1 stoichiometry for the reaction between nitrite and ammonium indicated that the transformations might be attributed to the anammox process. Attempts to find other anaerobic ammonium-oxidizing processes in this sediment failed. The apparent K_m of nitrite consumption was less than 3 μM, and the relative importance of ammonium oxidation with nitrite and denitrification for the production of nitrogen gas was independent of nitrite concentration. Thus, the quantitative importance of ammonium oxidation with nitrite in the jar incubations at elevated nitrite concentrations probably represents the in situ situation. With the addition of nitrate, the production of nitrite from nitrate was four times faster than its consumption and therefore did not limit the rate of ammonium oxidation. Accordingly, the rate of this process was the same whether nitrate or nitrite was added as electron acceptor. The addition of organic matter did not stimulate denitrification, possibly because it was outcompeted by manganese reduction or because transport limitation was removed due to homogenization of the sediment.     

Oxygen and carbon dioxide fluxes from barley shoots depend on nitrate assimilation

A custom oxygen analyzer in conjunction with an infrared carbon dioxide analyzer and humidity sensors permitted simultaneous measurements of oxygen, carbon dioxide, and water vapor fluxes from the shoots of intact barley plants (Hordeum vulgare L. cv Steptoe). The oxygen analyzer is based on a calciazirconium sensor and can resolve concentration differences to within 2 microliters per liter against the normal background of 210,000 microliters per liter. In wild-type plants receiving ammonium as their sole nitrogen source or in nitrate reductase-deficient mutants, photosynthetic and respiratory fluxes of oxygen equaled those of carbon dioxide. By contrast, wild-type plants exposed to nitrate had unequal oxygen and carbon dioxide fluxes: oxygen evolution at high light exceeded carbon dioxide consumption by 26% and carbon dioxide evolution in the dark exceeded oxygen consumption by 25%. These results indicate that a substantial portion of photosynthetic electron transport or respiration generates reductant for nitrate assimilation rather than for carbon fixation or mitochondrial electron transport.     

Bio-electrochemical removal of nitrate from water and wastewater--a review

Nitrates in different water and wastewater streams raised concerns due to severe impacts on human and animal health. Diverse methods are reported to remove nitrate from water streams which almost fail to entirely treat nitrate, except biological denitrification which is capable of reducing inorganic nitrate compounds to harmless nitrogen gas. Review of numerous studies in biological denitrification of nitrate containing water resources, aquaculture wastewaters and industrial wastewater confirmed the potential of this method and its flexibility towards the remediation of different concentrations of nitrate. The denitrifiers could be fed with organic and inorganic substrates which have different performances and subsequent advantages or disadvantages. Review of heterotrophic and autotrophic denitrifications with different food and energy sources concluded that autotrophic denitrifiers are more effective in denitrification. Autotrophs utilize carbon dioxide and hydrogen as the source of carbon substrate and electron donors, respectively. The application of this method in bio-electro reactors (BERs) has many advantages and is promising. However, this method is not so well established and documented. BERs provide proper environment for simultaneous hydrogen production on cathodes and appropriate consumption by immobilized autotrophs on these cathodes. This survey covers various designs and aspects of BERs and their performances.     

Responses of nitrogen metabolism in N-sufficient barley primary leaves to plant growth in elevated atmospheric carbon dioxide

Effects of atmospheric carbon dioxide enrichment on nitrogen metabolism were studied in barley primary leaves (Hordeum vulgare L. cv. Brant). Seedlings were grown in chambers under ambient (36 Pa) and elevated (100 Pa) carbon dioxide and were fertilized daily with complete nutrient solution providing 12 millimolar nitrate and 2.5 millimolar ammonium. Foliar nitrate and ammonium were 27% and 42% lower (P ≤ 0.01) in the elevated compared to ambient carbon dioxide treatments, respectively. Enhanced carbon dioxide affected leaf ammonium levels by inhibiting photorespiration. Diurnal variations of total nitrate were not observed in either treatment. Total and Mg²⁺inhibited nitrate reductase activities per gram fresh weight were slightly lower (P ≤ 0.01) in enhanced compared to ambient carbon dioxide between 8 and 15 DAS. Diurnal variations of total nitrate reductase activity in barley primary leaves were similar in either treatment except between 7 and 10 h of the photoperiod when enzyme activities were decreased (P ≤ 0.05) by carbon dioxide enrichment. Glutamate was similar and glutamine levels were increased by carbon dioxide enrichment between 8 and 13 DAS. However, both glutamate and glutamine were negatively impacted by elevated carbon dioxide when leaf yellowing was observed 15 and 17 DAS. The above findings showed that carbon dioxide enrichment produced only slight modifications in leaf nitrogen metabolism and that the chlorosis of barley primary leaves observed under enhanced carbon dioxide was probably not attributable to a nutritionally induced nitrogen limitation. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Intercellular Spaces of the Avena Coleoptile

In the transverse sections of fresh Avena coleoptile certain intercellular spaces are transparent, others are dark. The transparent spaces represent the result of water-logging of the originally water-lined air passages. The dark spaces are lined with a plastic lipid-containing membrane which can be impregnated with melted paraffin. In the living tissue this membrane can be cut transversely and the cut sections presumably seal off the gas inside thus causing the dark interfacial refraction. Because of the high permeability of lipids to carbon dioxide and the virtual impermeability to oxygen and nitrogen, there is a reason to believe that the lipid-lined spaces are filled with gas rich in carbon dioxide, and the lipid membrane may function as a regulator of the diffusion pressure of this gas.     

Effect of helium on the respiration and glycolysis of mouse liver slices

It has been shown that helium has the ability to affect variously the rates of certain metabolic reactions in vitro as compared to nitrogen. An attempt has been made to approximate the sites of action in mouse liver preparations. The following results have been obtained by the substitution of a mixture of 80 per cent helium and 20 per cent oxygen for air: (a) An increase in the rate of oxygen consumption and carbon dioxide production to the same degree, the respiratory quotient remaining unchanged. (b) A decrease in the magnitude of cyanide inhibition. The effectiveness of helium increases with the degree of the cyanide inhibition. (c) No effect on the activity of slices which have been poisoned with fluoride when either lactate or pyruvate has been added as a substrate. (d) A change in the rate, and the slope of the curve of oxygen consumption in liver homogenates which are utilizing pyruvate as a substrate. The use of helium relative to nitrogen under anaerobic conditions causes: (a) A depression of the glycolytic rates in both mouse liver slices and diaphragm. (b) An increase in the carbon dioxide evolution and lactic acid production of mouse liver homogenates oxidizing either glucose and hexose diphosphate, or hexose diphosphate alone. In neither slices nor homogenates does the addition of fluoride and the use of pyruvate as the hydrogen acceptor alter the fundamental response of the preparations. The following hypotheses have been advanced and discussed in order to explain the observed phenomena: 1. Helium does not alter the substrate utilized by the tissue. 2. The gas interferes in some way with the cyanide-cytochrome oxidase bond, but may not affect cytochrome oxidase in the absence of cyanide. 3. The citric acid cycle is not subject to the influence of helium in tissue slices, but is altered in an unexplained fashion in homogenates. It is postulated that a rearrangement of particulate surfaces may be the significant factor here. 4. The glycolytic cycle is the site of both an inhibitory and an acceleratory effect of helium. The locus of the inhibition lies above the aldolase reaction and that of the acceleration between the aldolase and enolase reactions.     

Fungicidal control of Macrophomina phaseolina altered in pathogenicity by substrate nutrients

The presence of different carbon and nitrogen sources and bivalent metal compounds in the substrate medium influenced the mycelial growth of Macrophomina phaseolina and in vitro susceptibility to fungicides. The inoculum from such substrate media showed differences in pathogenicity on mung bean (Vigna radiata). Sucrose and asparagine significantly increased the mycelial growth as well as pathogenicity of the fungus. Absence of bivalent metal ions, viz., Fe⁺⁺, Zn⁺⁺ and Mg⁺⁺ in the medium produced inoculum which caused maximum seedling mortality and foliage blight. Carbendazim and thiophanate-M as seed treatments were significantly less effective when the inoculum was from a medium containing glucose than when the inoculum was from a medium containing sucrose. Captafol and thiram gave significantly better disease control on mung bean when the inoculum used for soil inoculations was from media containing asparagine and ammonium nitrate compared to the inoculum grown on a medium containing sodium nitrate. Carbendazim, thiophanate-M, PMA, captafol and thiram gave good disease control when the inoculum used was raised on a medium devoid of bivalent metal ions. Carbendazim and thiophanate-M were the best fungicides as foliar treatments and controlled the disease irrespective of carbon, nitrogen and bivalent metal ion status of the substrate medium used for the production of inoculum.     

Control of photosynthesis during nitrogen depletion and recovery in a non-nitrogen-fixing cyanobacterium

When cells of Synechocystis strain PCC 6308 are starved for nitrogen, the amount of stored carbohydrate increases, the phycocyanin to chlorophyll a ratio decreases, and the rates of oxygen evolution and of carbon dioxide fixation decrease. When nitrate-nitrogen is replenished, the amount of carbohydrate decreases, the rate of oxygen evolution increases immediately, preceeding the increase in phycocyanin or carbon dioxide fixation. The rate of respiration first increases and then decreases upon nitrogen addition. Nitrogen-starved cells show no variable fluorescence; variable fluorescence recovered in parallel with oxygen evolution. This suggests that photosystem II is inactive in nitrogen depleted cells and not blocked by a build up of metabolic endproducts. Since carbon dioxide fixation does not increase until two to four hours after nitrate is replenished to nitrogen starved cells, it is suggested that reducing power may first be needed within the cell for some other process than photosynthesis, such as nitrate reduction.     

Indigenous Sediment Microbial Activity in Response to Nutrient Enrichment and Plant Growth Following a Controlled Oil Spill on a Freshwater Wetland

The population density and activity of a microbial community associated with the sediment and rhizosphere of an intertidal freshwater wetland dominated by Scirpus pungens was monitored before and following the application of weathered Mesa light crude oil and fertilizers. The influence of nutrient enrichment (fertilizers) and plant growth on oil degradation rates was determined from the resulting data. The study plots (four blocks of replicates) were subjected to five treatments: oil only (natural attenuation); oil plus ammonium nitrate and phosphate, with regular cropping of the plants; oil plus ammonium nitrate and phosphate; oil plus sodium nitrate and phosphate; no oil, ammonium nitrate and phosphate. The plots were regularly monitored in the field for gas production (carbon dioxide and nitrous oxide), and samples were collected for laboratory analysis of denitrification activity, aliphatic and aromatic hydrocarbon degradation activity, and total heteroptrophic bacteria.

The viable bacterial population density increased during the first 4 weeks in oiled and unoiled experimental plots that were fertilized. In contrast, population densities in untreated areas remained relatively unchanged throughout the monitoring period. The microbial population demonstrated a rapid and sustained increase in naphthalene mineralization activity in plots that were both fertilized and oiled. Hexadecane mineralization activity increased in response to fertilizer application, with ammonium nitrate causing a larger increase than sodium nitrate. A very significant difference observed in the mineralization of hexadecane was that the surface sediments were much more active than the subsurface sediments. This difference became even more pronounced in the second year of monitoring, even though the treatment regime had been discontinued. This compartmentalization of mineralization activity was not observed for naphthalene. Following fertilizer application, field and laboratory evaluation of nitrogen metabolism in the sediments indicated significant denitrification activity that was not adversely affected by oiling. The results demonstrated that the application of fertilizers stimulated the activities of indigenous hydrocarbon-degrading and denitrifying bacteria, and the presence of oil either enhanced or had no detrimental effect on these activities. As a remediation strategy, the application of fertilizers to a wetland shoreline following an oil spill would promote the growth of indigenous plants and their associated microbial flora, resulting in increased metabolic activity and the potential for increased oil degradation activity.     

A microcosm study of nitrogen utilization in the Great Salt Lake,Utah

Microcosms were used to study the effects of two inorganic nitrogen sources (ammonia and nitrate) and two organic nitrogen sources (urea and glutamic acid) on the growth of algae and bacteria found in the Great Salt Lake, Utah. Ammonia, nitrate and urea stimulated bacterial growth indirectly through increased algal production of unknown organic substances. Glutamic acid, representing readily available organic carbon and nitrogen, stimulated the bacteria directly. No nitrification was observed in the microcosms although nitrite was found when the microcosms were supplemented with nitrate. Lake sediment contained a number of anaerobic bacteria producing hydrogen sulfide, methane and other gases. Production of these gases was stimulated in the columns with high algal and bacterial activity.     

Indigenous Sediment Microbial Activity in Response to Nutrient Enrichment and Plant Growth Following a Controlled Oil Spill on a Freshwater Wetland

The population density and activity of a microbial community associated with the sediment and rhizosphere of an intertidal freshwater wetland dominated by Scirpus pungens was monitored before and following the application of weathered Mesa light crude oil and fertilizers. The influence of nutrient enrichment (fertilizers) and plant growth on oil degradation rates was determined from the resulting data. The study plots (four blocks of replicates) were subjected to five treatments: oil only (natural attenuation); oil plus ammonium nitrate and phosphate, with regular cropping of the plants; oil plus ammonium nitrate and phosphate; oil plus sodium nitrate and phosphate; no oil, ammonium nitrate and phosphate. The plots were regularly monitored in the field for gas production (carbon dioxide and nitrous oxide), and samples were collected for laboratory analysis of denitrification activity, aliphatic and aromatic hydrocarbon degradation activity, and total heteroptrophic bacteria. The viable bacterial population density increased during the first 4 weeks in oiled and unoiled experimental plots that were fertilized. In contrast, population densities in untreated areas remained relatively unchanged throughout the monitoring period. The microbial population demonstrated a rapid and sustained increase in naphthalene mineralization activity in plots that were both fertilized and oiled. Hexadecane mineralization activity increased in response to fertilizer application, with ammonium nitrate causing a larger increase than sodium nitrate. A very significant difference observed in the mineralization of hexadecane was that the surface sediments were much more active than the subsurface sediments. This difference became even more pronounced in the second year of monitoring, even though the treatment regime had been discontinued. This compartmentalization of mineralization activity was not observed for naphthalene. Following fertilizer application, field and laboratory evaluation of nitrogen metabolism in the sediments indicated significant denitrification activity that was not adversely affected by oiling. The results demonstrated that the application of fertilizers stimulated the activities of indigenous hydrocarbon-degrading and denitrifying bacteria, and the presence of oil either enhanced or had no detrimental effect on these activities. As a remediation strategy, the application of fertilizers to a wetland shoreline following an oil spill would promote the growth of indigenous plants and their associated microbial flora, resulting in increased metabolic activity and the potential for increased oil degradation activity.     

Carbon dioxide increases acid resistance in Escherichia coli

AIMS: To investigate how carbon dioxide affects the acid resistance of Escherichia coli. METHODS AND RESULTS: Escherichia coli W3110 was grown in minimal EG medium at pH 7.5, and cells were adapted at pH 5.5 at 37 degrees C with and without supply of carbon dioxide and nitrogen gases. The number of colonies grown on LB medium was measured after cells were challenged in minimal EG medium of pH 2.5 at 37 degrees C under various conditions. When carbon dioxide was supplied at both the acid adaptation and challenge stages, 94% of cells survived after the acid challenge for 1 h, while the survival rates were 50 and 67% when nitrogen gas and glutamate were supplied respectively. After the acid challenge for 3 h, the survival rate observed with the carbon dioxide gas supply was again 2.5-fold higher than those with the nitrogen gas supply. CONCLUSION: Carbon dioxide was shown to participate in the maintenance of high viability under acidic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides useful information for research into bacterial pathogenesis, fermentation and food preservation.