Studies on the lipid content and phosphate requirement of glucose- and acetate-grown Escherichia coli

1. The phosphate requirement, i.e. the concentration of inorganic orthophosphate that just ceases to be limiting for growth, of Escherichia coli N.C.T.C. 5928 was determined for growth in ammonium-salts media containing glucose or acetate as the carbon and energy source, and compared with that of six other strains of E. coli. 2. The phosphate requirement for E. coli N.C.T.C. 5928 growing on acetate was about ten times that for growth on glucose, but this difference was not observed with any of the other strains. 3. After about 40 generations' growth on acetate with phosphate limitation in a chemostat, the phosphate requirement of the cells gradually decreased until it was equivalent to that of the glucose-grown organism; a single passage through glucose batch culture sufficed to restore the original high phosphate requirement, indicating a permeability phenomenon. 4. The lipid content of E. coli N.C.T.C. 5928 grown on glucose or acetate was measured isotopically by fractionation of cells grown on inorganic [(32)P]orthophosphate and gravimetrically after extraction from the cells by three different methods; change of carbon source from glucose to acetate did not affect the lipid content, which remained constant at 8-9% of the bacterial dry weight.     

Influence of growth temperature on glucose metabolism of a psychotrophic strain of Bacillus cereus.

The influence of temperature on glucose metabolism of a psychotrophic strain of Bacillus cereus was investigated. The pH of the growth medium and spore-forming frequencies of B. cereus varied when grown at 32, 20, or 7 C. Radiorespirometric analyses revealed that vegetative cells of B. cereus metabolized glucose by simultaneous operation of the Embden-Meyerhof-Parnas pathway and the pentose phosphate pathway. As the growth temperature decreased, glucose was metabolized with increased participation of the pentose phosphate pathway. The shift of cells grown at a higher temperature to a lower temperature increased the relative participation of the pentose phosphate pathway, whereas the shift of cells grown at low temperatures to a higher temperature had the opposite effect. Cells of late logarithmic phase grown at 20 and 7 C oxidized acetate by the tricarboxylic acid cycle reaction. However, cells grown at 32 C failed to oxidize acetate to CO2 to any appreciable extent. The extracellular products resulting from the metabolism of glucose decreased as the growth temperature was lowered. Organic acids were the major extracellular products of cultures grown at 32 and 20 C. Acetic acid, lactic acid, and pyruvic acid together accounted for 86.1 and 78.9% of extracellular radioactivity, respectively, at the two temperatures. The relative ratio of these three acids varied between the temperatures. Little or no acid accumulated at 7 C.     

Influence of growth temperature on glucose metabolism of a psychotrophic strain of Bacillus cereus.

The influence of temperature on glucose metabolism of a psychotrophic strain of Bacillus cereus was investigated. The pH of the growth medium and spore-forming frequencies of B. cereus varied when grown at 32, 20, or 7 C. Radiorespirometric analyses revealed that vegetative cells of B. cereus metabolized glucose by simultaneous operation of the Embden-Meyerhof-Parnas pathway and the pentose phosphate pathway. As the growth temperature decreased, glucose was metabolized with increased participation of the pentose phosphate pathway. The shift of cells grown at a higher temperature to a lower temperature increased the relative participation of the pentose phosphate pathway, whereas the shift of cells grown at low temperatures to a higher temperature had the opposite effect. Cells of late logarithmic phase grown at 20 and 7 C oxidized acetate by the tricarboxylic acid cycle reaction. However, cells grown at 32 C failed to oxidize acetate to CO2 to any appreciable extent. The extracellular products resulting from the metabolism of glucose decreased as the growth temperature was lowered. Organic acids were the major extracellular products of cultures grown at 32 and 20 C. Acetic acid, lactic acid, and pyruvic acid together accounted for 86.1 and 78.9% of extracellular radioactivity, respectively, at the two temperatures. The relative ratio of these three acids varied between the temperatures. Little or no acid accumulated at 7 C.     

Diauxic growth in Azotobacter vinelandii.

Azotobacter vinelandii exhibited diauxie when grown in a medium containing both acetate and glucose as carbon sources. Acetate was used as the primary carbon source during the acetate-glucose diauxie. Uptake of acetate was constitutively expressed during both diauxic phases of growth. Induction of the glucose uptake system was inhibited in the presence of acetate. Acetate was also the preferred growth substrate for A. vinelandii grown in a medium containing either fructose, maltose, xylitol, or mannitol. The tricarboxylic acid cycle intermediates citrate, isocitrate, and 2-oxoglutarate inhibited glucose utilization in cells grown in glucose medium containing these substrates, and diauxic growth was observed under these growth conditions. Temporal expression of isocitrate-lyase, ATPase, and nitrogenase was exhibited during acetate-glucose diauxie.     

Control of diauxic growth of Azotobacter vinelandii on acetate and glucose.

Batch cultures of Azotobacter vinelandii were inoculated with cells pregrown on either acetate or glucose. When they were subsequently grown on a mixture of acetate and glucose, typical diauxic growth was observed, with preferential uptake of acetate in the first and glucose in the second phase of growth. Extracts from acetate-pregrown cells exhibited high acetate kinase activity in the first phase of growth. This activity decreased and activities of the two glucose enzymes glucose 6-phosphate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase increased in the second phase. Extracts from glucose-pregrown cells exhibited high initial activities of the two glucose enzymes, which decreased while acetate kinase activity increased in the first phase of growth. Again, in the second phase, activities of the two glucose enzymes increased and acetate kinase activity decreased. In any case, isocitrate dehydrogenase activity varied only slightly and unspecifically. The differences in enzyme activity and the constancy of isocitrate dehydrogenase were confirmed by experiments with either acetate- or glucose-limited chemostats. In chemostats in which both of the substrates were limiting, all of the enzymes displayed significant activities. Glucose 6-phosphate dehydrogenase activity was inhibited by acetyl coenzyme A and acetyl phosphate but not by acetate. It is proposed that diauxic growth is based on the control of enzymes involved in acetate or glucose dissimilation by which acetate or its metabolites control the expression and activity of glucose enzymes.     

Initiation of Yeast Sporulation by Partial Carbon, Nitrogen, or Phosphate Deprivation

In this paper we show that partial deprivation of a carbon source, a nitrogen source, or phosphate in the presence of all other nutrients needed for growth initiates meiosis and sporulation of Saccharomyces cerevisiae homothallic strain Y55. For carbon deprivation experiments, cells were grown in synthetic medium (pH 5.5) containing an excess of one carbon source and then transferred to the same medium containing different concentrations of the same carbon source. In the case of transfer to different acetate concentrations, the log optical density at 600 nm increased at the previous rate until the cells had used up all of the acetate, whereupon the cells entered a stationary phase and did not sporulate. The same was observed with ethanol. In contrast, at different concentrations of dihydroxy-acetone or pyruvate, cells grew at different rates and sporulated optimally at intermediate concentrations (50 to 75 mM). The response to galactose was similar but reflected the presence of a low-affinity galactose transport system and the induction of a high-affinity galactose transport system. Cells could also sporulate when a glucose medium ran out of glucose, apparently because they initiated sporulation during the subsequent lag period and then used the produced ethanol as a carbon source. For phosphate deprivation experiments, cells growing with excess ethanol or pyruvate and phosphate were transferred to the same medium containing limiting amounts of phosphate. First, they used up the intracellular phosphate reserves for rapid growth, and then they sporulated optimally when an intermediate concentration (30 μM) of phosphate had been added to the medium. For nitrogen deprivation experiments, cells grown with excess acetate, ethanol, or pyruvate and NH₄⁺ were transferred to the same medium from which all nitrogen had been removed. These cells sporulated well in acetate medium but poorly in ethanol and pyruvate media. However, the sporulation frequency in the latter media could be increased greatly by adding intermediate concentrations (1 mM) of the slowly metabolizable amino acids glycine, histidine, or phenylalanine. If one assumes that the sporulation response to partial deprivation of carbon-, nitrogen-, or phosphorus-containing compounds reflects control by a single metabolite, the intracellular concentration of this metabolite may decide at the START position (G1 phase) of the cell cycle whether a/α cells enter mitosis or meiosis.     

Very slow growth of Escherichia coli.

A recycling fermentor (a chemostat with 100% biomass feedback) was used to study glucose-limited behavior of Escherichia coli B. The expectation from mass transfer analysis that growth would asymptotically approach a limit mass determined by the glucose provision rate (GPR) and the culture's maintenance requirement was not met. Instead, growth proceeded at progressively lower rates through three distinct phases. After the fermentor was seeded, but before glucose became limiting, growth followed the usual, exponential path (phase 1). About 12 h postseeding, residual glucose in the fermentor fell below 1 microgram . ml-1 and the growth rate (dx/dt) became constant and a linear function of GPR (phase 2). The specific growth rate, mu, therefore fell continuously throughout the phase. Biomass yield and glucose assimilation (13%) were near the level for exponential growth, however, and independent of GPR over a broad range. At a critical specific growth rate (0.04 h-1 for this strain), phase 2 ended abruptly and phase 3 commenced. In phase 3, the growth rate was again constant, although lower than in phase 2, so that mu continued to fall, but growth rates and yields were praboloid functions of GPR. They were never zero, however, at any positive value of GPR. By inference, the fraction of metabolic energy used for maintenance functions is constant for a given GPR, although different for phases 2 and 3, and independent of biomass. In both phases 2 and 3, orcinol, diphenylamine, and Lowry reactive materials were secreted at near-constant rates such that over 50% as much biosynthetic mass was secreted as was retained by the cells.     

Effect of sugars on D-arabitol production and glucose metabolism in Saccharomyces rouxii.

The effect of sugars on the production of d-arabitol and on the glucose catabolic pathways was investigated in the osmotrophic yeast Saccharomyces rouxii. The activity of d-arabitol dehydrogenase, which served as a measure of total d-arabitol production, increased when cells were grown in the presence of increasing glucose concentrations. Growth in sucrose had no effect on the enzyme activity. A high intracellular concentration of d-arabitol could be demonstrated when the cells were grown in a 60% glucose medium and could be eliminated by anaerobic growth or growth in the presence of 4 mg of chloramphenicol per ml. A mutant was isolated that would not grow in 60% glucose; although the regulation of d-arabitol dehydrogenase was altered in this strain, the production of d-arabitol was not eliminated. The activity of d-arabitol dehydrogenase followed the growth phases of the parent strain when the cells were preadapted to 30% glucose. If the cells were adapting from 1 to 30% glucose, a large increase in enzyme activity was detected before growth occurred. Protein synthesis was found to be involved in this increase in activity. There was an increased participation of the pentose phosphate pathway when the cells were grown in the presence of increasing glucose concentrations. The mutant strain had only an 11% pentose phosphate pathway participation compared with 20% for the parent strain in glucose. The results suggest that the active pentose phosphate pathway is involved in glucose tolerance by providing a plentiful supply of reduced nicotinamide adenine dinucleotide phosphate which is necessary for cell survival.     

A microcalorimetric study of the growth of Klebsiella aerogenes in simple salts/glucose media.

Heat output-time records or 'thermograms' produced during the aerobic growth of Klebsiella aerogenes in simple salts/glucose media with growth limiting glucose concentrations of 2.0, 1.0 and 0.5 g dm-3 were obtained using a flow-microcalorimeter fitted with an aerobic cell. These traces are interpreted in terms of the recorded oxygen tension, pH, glucose concentration and bacterial population of the culture. Heat output is greatest during the phase of exponential growth, indicating that here the organisms are most energetically inefficient. During the stationary phase aerobic processes, which give rise to a low oxygen tension, produce a smaller heat output until secondary metabolic processes are complete.     

Analysis of growth of Gluconobacter oxydans in glucose containing media

Gluconobacter oxydans oxidizes glucose via alternative pathways: one involves the non-phosphorylative, direct oxidation route to gluconic acid and ketogluconic acids, and the second requires an initial phosphorylation and then oxidation via the pentose phosphate pathway enzymes. During growth of G. oxydans in glucose-containing media, the activity of this pathway is strongly influenced by (1) the pH value of the environment and (2) the actual concentration of glucose present in the culture. At pH values below 3.5 the activity of the pentose phosphate pathway was completely inhibited resulting in an increased requirement of the organism for nutrient substances, and a poor cell yield. At pH 5.5 a triphasic growth response was observed when G. oxydans was grown in a defined medium. Above a threshold value of 5–15 mM glucose, oxidation of both glucose and gluconate by the pentose phosphate pathway enzymes was repressed, causing a rapid accumulation of gluconic acid in the culture medium. When growing under these conditions, a low affinity for the oxidation of glucose was found (K _s=13 mM). Below this threshold glucose concentration, pentose phosphate pathway enzymes were synthesized and glucose was actively assimilated via this pathway. It was shown that de novo enzyme synthesis was necessary for increased pentose phosphate pathway activity and that assimilation of gluconate by washed cell suspensions was inhibited by glucose.     

High growth rate and substrate exhaustion results in rapid cell death and lysis in the thermophilic bacterium Geobacillus thermoleovorans

Batch cultures of the thermophilic bacterium Geobacillus thermoleovorans T80 attained extremely high-specific glucose utilization rates leading to high specific growth rates, followed by extensive cell death and lysis with the onset of substrate exhaustion. The dramatic decrease in live cell numbers, as determined by flow cytometry, was accompanied by the release of soluble protein. Once the growth phase reached the point of commitment to lysis created by the impending exhaustion of substrate, the addition of extra carbon substrate did not halt the rapid death rate and lysis, although, towards the end of the exponential growth phase, the substrate was utilized producing only a small additional biomass concentration as a result of the net effect of cell growth and death. This lytic phenomenon was observed when a range of different carbon substrates (glucose, pyruvate, acetate, n-hexadecane, nutrient broth), as well as ammonium (the nitrogen source) in the presence of excess carbon source, reached near exhaustion. The rate and extent of cell death and the ensuing lysis depend on the culture growth rate. Cultures batch grown with a lower initial substrate concentration, or at a lower temperature, or at lower dilution rates for continuous-flow cultures, exhibited a lower rate and extent of cell death and lysis. Batch re-culture of the persister cells resulted in a behavior identical to that of the original culture indicating that these cells were not genetically modified. The glucose utilization, cell growth and death rates were mathematically described based on Monod kinetics and estimated values of pertinent biokinetic constants are reported.     

Mechanisms of acetate formation and acetate activation in halophilic archaea

The halophilic archaea Halococcus (Hc.) saccharolyticus, Haloferax (Hf.) volcanii, and Halorubrum (Hr.) saccharovorum were found to generate acetate during growth on glucose and to utilize acetate as a growth substrate. The mechanisms of acetate formation from acetyl-CoA and of acetate activation to acetyl-CoA were studied. Hc. saccharolyticus, exponentially growing on complex medium with glucose, formed acetate and contained ADP-forming acetyl-CoA synthetase (ADP-ACS) rather than acetate kinase and phosphate acetyltransferase or AMP-forming acetyl-CoA synthetase. In the stationary phase, the excreted acetate was completely consumed, and cells contained AMP-forming acetyl-CoA synthetase (AMP-ACS) and a significantly reduced ADP-ACS activity. Hc. saccharolyticus, grown on acetate as carbon and energy source, contained only AMP-ACS rather than ADP-ACS or acetate kinase. Cell suspensions of Hc. saccharolyticus metabolized acetate only when they contained AMP-ACS activity, i.e., when they were obtained after growth on acetate or from the stationary phase after growth on glucose. Suspensions of exponential glucose-grown cells, containing only ADP-ACS but not AMP-ACS, did not consume acetate. Similar results were obtained for the phylogenetic distantly related halophilic archaea Hf. volcanii and Hf. saccharovorum. We conclude that, in halophilic archaea, the formation of acetate from acetyl-CoA is catalyzed by ADP-ACS, whereas the activation of acetate to acetyl-CoA is mediated by an inducible AMP-ACS.Abbreviations. Hc. Halococcus - Hf. Haloferax - Hr. Halorubrum - Hb. Halobacterium An erratum to this article can be found at     

Energetics of Bacillus stearothermophilus growth: molar growth yield and temperature effects on growth efficiency.

The major growth yield of a prototrophic strain of Bacillus stearothermophilus under aerobic conditions on salts medium containing ammonium nitrate as the nitrogen source and glucose or succinate as the carbon source was maximal at the lowest growth temperature employed and decreased steadily as the temperature was raised. The temperature optima for growth yield and for growth rate were thus different. The molar growth yield values of the thermophile, especially at the lower growth temperatures, were similar to those reported for aerobically grown mesophilic bacteria, both on glucose and on succinate. At the higher growth temperatures, a lower proportion of glucose carbon was incorporated into cells and a correspondingly greater proportion was left incompletely utilized in the medium, mostly as acetate. This suggests a greater inefficiency in the coordination of the nonoxidative and oxidative phases of glucose metabolism at the gigher temperatures. Another factor causing a decreased cell yield at higher temperatures was possibly an uncoupling of energy production from respiration. The rates of respiration by intact cells of the thermophile on glucose and on succinate followed the Arrhenius relationship from 55 C to 20 C, which is some 20 C below the minimal growth temperature of the organism. The Arrhenius constant was 17.1 kcal/mol for glucose oxidation and 13.5 kcal/mol for succinate oxidation. These results are comparable to those reported for some mesophiles, and they suggest that the inability of the thermophile to grow at temperatures below about 41 C is not due to an abnormally high temperature coefficient for the uptake and oxidation of the carbon source.     

Comparison of growth, acetate production, and acetate inhibition of Escherichia coli strains in batch and fed-batch fermentations

The growth characteristics and acetate production of several Escherichia coli strains were compared by using shake flasks, batch fermentations, and glucose-feedback-controlled fed-batch fermentations to assess the potential of each strain to grow at high cell densities. Of the E. coli strains tested, including JM105, B, W3110, W3100, HB101, DH1, CSH50, MC1060, JRG1046, and JRG1061, strains JM105 and B were found to have the greatest relative biomass accumulation, strain MC1060 accumulated the highest concentrations of acetic acid, and strain B had the highest growth rates under the conditions tested. In glucose-feedback-controlled fed-batch fermentations, strains B and JM105 produced only 2 g of acetate.liter-1 while accumulating up to 30 g of biomass.liter-1. Under identical conditions, strains HB101 and MC1060 accumulated less than 10 g of biomass.liter-1 and strain MC1060 produced 8 g of acetate.liter-1. The addition of various concentrations of sodium acetate to the growth medium resulted in a logarithmic decrease, with respect to acetate concentration, in the growth rates of E. coli JM105, JM105(pOS4201), and JRG1061. These data indicated that the growth of the E. coli strains was likely to be inhibited by the acetate they produced when grown on media containing glucose. A model for the inhibition of growth of E. coli by acetate was derived from these experiments to explain the inhibition of acetate on E. coli strains at neutral pH.     

Function of Growth Factors for Rumen Microorganisms I. Nutritional Characteristics of Selenomonas ruminantium

Nutritional characteristics of Selenomonas ruminantium var. lactilytica isolated from a sheep rumen were studied. The organism required for growth the addition of a clarified rumen fluid to a Trypticase-yeast extract medium with either lactate or glucose as an energy source. The requirement for rumen fluid was found to be satisfied by volatile fatty acids in glucose media and by biotin in lactate media. Straight-chain saturated fatty acids with C(3) to C(10) carbon skeleton had been found to be effective. Among them, n-valerate was most effective at the lowest concentration. An abnormal morphology was observed with n-valerate-deficient glucose media. n-Valerate was essential in glucose media, and it was stimulatory in lactate media. Fermentation products from glucose were lactate, propionate, and acetate, and fermentation products from lactate were propionate and acetate. When cells were grown in a glucose medium containing n-valerate-C(14), the label was present in cell fractions. Almost all of the activity was found in lipid materials.     

Effects of trialkyllead compounds on growth, respiration and ion transport in Escherichia coli K12

Triethyllead and tripropyllead cations affected growth, energy metabolism and ion transport in Escherichia coli K12. The tripropyllead compound was more liposoluble than the triethyl analogue and was also more effective in inhibiting cell growth and the oxygen uptake of both intact cells and membrane particles. Triethyllead acetate (5 microM) inhibited growth on non-fermentable carbon sources, such as glycerol and succinate, more markedly than on glucose. At higher concentrations, triethyllead caused significant inhibition of respiration rates of intact cells; the concentration giving 50% inhibition was 60 microM for glycerol-grown cells and 150 microM for glucose-grown cells. Oxidation of succinate by membrane particles was less sensitive to inhibition by the tripropyl- or triethyllead compounds than were the oxidations of DL-lactate or NADH. Triethyllead acetate [1.9 mumol (mg membrane protein)-1] inhibited the reduction by NADH of cytochromes; evidence for more than one site of inhibition in the respiratory chain was obtained. Membrane-bound ATPase activity was strongly inhibited by triethyllead acetate in the absence or presence of Cl-. The concentration of inhibitor giving 50% inhibition [0.02 mumol (mg membrane protein)-1] was about two orders of magnitude lower than that required for 50% inhibition of substrate oxidation rates in membranes. Triethyllead acetate (1 microM) induced swelling of spheroplasts in iso-osmotic solutions of either NH4Cl or NH4Br, presumably as a result of the mediation by the organolead compound of Cl-/OH- and Br-/OH- antiports across the cytoplasmic membrane. Similar exchanges of OH- for F-, NO3- or SO4(2)- or the uniport of H+ could not be demonstrated. Comparisons are drawn between the effects of trialkyllead compounds and those of the more widely studied trialkyltin compounds.     

Comparison of growth, acetate production, and acetate inhibition of Escherichia coli strains in batch and fed-batch fermentations.

The growth characteristics and acetate production of several Escherichia coli strains were compared by using shake flasks, batch fermentations, and glucose-feedback-controlled fed-batch fermentations to assess the potential of each strain to grow at high cell densities. Of the E. coli strains tested, including JM105, B, W3110, W3100, HB101, DH1, CSH50, MC1060, JRG1046, and JRG1061, strains JM105 and B were found to have the greatest relative biomass accumulation, strain MC1060 accumulated the highest concentrations of acetic acid, and strain B had the highest growth rates under the conditions tested. In glucose-feedback-controlled fed-batch fermentations, strains B and JM105 produced only 2 g of acetate.liter-1 while accumulating up to 30 g of biomass.liter-1. Under identical conditions, strains HB101 and MC1060 accumulated less than 10 g of biomass.liter-1 and strain MC1060 produced 8 g of acetate.liter-1. The addition of various concentrations of sodium acetate to the growth medium resulted in a logarithmic decrease, with respect to acetate concentration, in the growth rates of E. coli JM105, JM105(pOS4201), and JRG1061. These data indicated that the growth of the E. coli strains was likely to be inhibited by the acetate they produced when grown on media containing glucose. A model for the inhibition of growth of E. coli by acetate was derived from these experiments to explain the inhibition of acetate on E. coli strains at neutral pH.     

Modeling growth and off-flavours production of spoiled beer bacteria, Pectinatus frisingensis

The genus Pectinatus includes strictly anaerobic Gram-negative non-spore-forming mesophilic bacteria often referred to as beer-spoilage bacteria. Pectinatus frisingensis was chosen as the reference strain. The organisms were grown in batch cultures under stringent anaerobic conditions in a synthetic medium and with pH regulation. Various glucose and lactate concentrations were used, and a low inoculum reproduced spoilage conditions in bottled beer. Propionate and acetate are the major compounds responsible for the off-flavour of beer. Gompertz curves were fitted to acid-biomass production and glucose consumption; thereby the lag-phase, production rate and final concentrations were derived. Volatile fatty acids production began 19 h after biomass growth. There was no lineareffect of substrate on final concentration of propionate, acetate and biomass. An additive model is proposed for the prediction of bacterial growth and acid production on both glucose and lactate.     

Influence of nitrate on oxalate- and glyoxylate-dependent growth and acetogenesis by Moorella thermoacetica

Oxalate and glyoxylate supported growth and acetate synthesis by Moorella thermoacetica in the presence of nitrate under basal (without yeast extract) culture conditions. In oxalate cultures, acetate formation occurred concomitant with growth and nitrate was reduced in the stationary phase. Growth in the presence of [(14)C]bicarbonate or [(14)C]oxalate showed that CO(2) reduction to acetate and biomass or oxalate oxidation to CO(2) was not affected by nitrate. However, cells engaged in oxalate-dependent acetogenesis in the presence of nitrate lacked a membranous b-type cytochrome, which was present in cells grown in the absence of nitrate. In glyoxylate cultures, growth was coupled to nitrate reduction and acetate was formed in the stationary phase after nitrate was totally consumed. In the absence of nitrate, glyoxylate-grown cells incorporated less CO(2) into biomass than oxalate-grown cells. CO(2) conversion to biomass by glyoxylate-grown cells decreased when cells were grown in the presence of nitrate. These results suggest that: (1) oxalate-grown cells prefer CO(2) as an electron sink and bypass the nitrate block on the acetyl-CoA pathway at the level of reductant flow and (2) glyoxylate-grown cells prefer nitrate as an electron sink and bypass the nitrate block of the acetyl-CoA pathway by assimilating carbon via an unknown process that supplements or replaces the acetyl-CoA pathway. In this regard, enzymes of known pathways for the assimilation of two-carbon compounds were not detected in glyoxylate- or oxalate-grown cells.     

Adhering ability of Stenotrophomonas maltophilia is dependent on growth conditions

The growth conditions are known to influence the bacterial adhesion to different kinds of surfaces. In the present study the adhering ability of Stenotrophomonas maltophilia, on growth in nutrient rich media (Tryptic Soy Broth (TSB)) and minimal media (Luria Bertani (LB)) was checked by viable cell count and spectrophotometric method. TSB grown S. maltophilia showed higher adhesion compared to bacteria grown in LB broth, to both biotic and abiotic surfaces. However, when bacteria were grown in LB broth supplemented with different concentrations of glucose, under aerobic conditions, the bacteria grown at lower glucose concentration (2 gm/l) showed maximum adhesion to abiotic surfaces (polystyrene microtiter plate) compared to biotic surfaces (mouse trachea, mouse tracheal mucus and HEp-2 cells line). Maximum adhesion to biotic surfaces was seen with cells grown at 4 gm/l of glucose concentration. On the contrary if the cell was grown under microaerophilic conditions maximum adhesion to abiotic and biotic surfaces was achieved with bacteria grown at 1 gm/l and 2 gm/l of glucose concentration respectively. A negative correlation was observed between glucose concentrations and pH of media, the latter declined faster under microaerophilic conditions as compared to aerobic condition.