Analysis of Escherichia coli Flagellin Gene Expression in Simulated Spaceflight Growth Conditions

Population growth curves of Escherichia coli (E. coli) cultures propagated in spaceflight environments demonstrate an extended log phase duration and an increased final cell concentration compared to E. coli cultures grown on Earth. We suggest that during spaceflight, a lack of convective mixing in the growth medium alters a cell’s microenvironment such that the cell at first devotes its resources primarily to motility and later shifts most of its resources to reproduction. As flagellin is the major protein component of flagella, the motility structure of E. coli, we propose that the expression of the flagellin gene (fliC) can be used as a diagnostic marker for determining if the bacterium is in fact altering its allocation of cellular resources to motility during specific growth phases. We have used semiquantitative RT-PCR to analyze the expression of fliC in cultures grown in laboratory apparatus that simulate various aspects of the spaceflight environment. The data from this pilot study indicate that fliC expression increases initially under stationary, slow clinorotation, and fast clinorotation growth conditions, peaking at mid-exponential phase and decreasing dramatically in stationary phase. These data support the hypothesis that metabolic resources are being directed towards forming the flagellum, the bacteria motile structure, before shifting resources to growth, reproduction, and maintenance.

Analysis of Escherichia coli Flagellin Gene Expression in Simulated Spaceflight Growth Conditions

SummaryPopulation growth curves of Escherichia coli (E. coli) cultures propagated in spaceflight environments demonstrate an extended log phase duration and an increased final cell concentration compared to E. coli cultures grown on Earth. We suggest that during spaceflight, a lack of convective mixing in the growth medium alters a cell’s microenvironment such that the cell at first devotes its resources primarily to motility and later shifts most of its resources to reproduction. As flagellin is the major protein component of flagella, the motility structure of E. coli, we propose that the expression of the flagellin gene (fliC) can be used as a diagnostic marker for determining if the bacterium is in fact altering its allocation of cellular resources to motility during specific growth phases. We have used semiquantitative RT-PCR to analyze the expression of fliC in cultures grown in laboratory apparatus that simulate various aspects of the spaceflight environment. The data from this pilot study indicate that fliC expression increases initially under stationary, slow clinorotation, and fast clinorotation growth conditions, peaking at mid-exponential phase and decreasing dramatically in stationary phase. These data support the hypothesis that metabolic resources are being directed towards forming the flagellum, the bacteria motile structure, before shifting resources to growth, reproduction, and maintenance.

Nonlinear Dynamics of Brewing Yeast Cell Growth in Alginate Micro-Beads

The nonlinear dynamics of brewing yeast cell growth in porous Ca-alginate matrices is considered experimentally and theoretically. The applications of alginate matrices include the reduction of internal mass transfer resistance, minimized cell leakage and growth restriction due to interactions between matrices and cell membranes comparatively to free cell culture conditions. The effects of micro-bead diameters in the range 0.3-2.0 mm on yeast cell growth were investigated. The stochastic mathematical model from the Langevin class is proposed for the interpretation of cell growth, affected by four micro-processes: micro-environmental quality changes due to nutrient diffusion into the micro-beads, cell leakage, repulsive interactions between boundary layers around the cells themselves, which contribute to the dynamics of cell growth as a negative, nonlinear feedback restriction and random kinetics effects. Such a model is used for the prediction of the optimal diameter of micro-beads, which ensures maximal final cell concentration. The results of cell growth in alginate matrices study have indicated an optimal diameter of 0.5-0.6 mm for micro-beads. Immobilized cells in these beads were not restricted significantly by mass transfer of nutrients and by cell leakage. The highest final cell concentration value indicated the largest feed-back restriction quantified by the constitutive parameter b.

Surface Pasteurization of Whole Fresh Cantaloupes Inoculated with Salmonella Poona or Escherichia coli †

Numerous outbreaks of salmonellosis by Salmonella Poona have been associated with the consumption of cantaloupe. Commercial washing processes for cantaloupe are limited in their ability to inactivate or remove this human pathogen. Our objective was to develop a commercial-scale surface pasteurization process to enhance the microbiological safety of cantaloupe. Populations of indigenous bacteria recovered from cantaloupes that were surface pasteurized at 96, 86, or 76°C for 2 to 3 min were significantly (P < 0.05) lower than those of the controls. Whole cantaloupes, surface inoculated with Salmonella Poona RM 2350 or Escherichia coli ATCC 25922 to a final cell concentration of ca. 5 log CFU/cm2 were stored at 4°C or room temperature (RT = 19 ± 1°C) for up to 72 h before processing. Treatments at 76°C for 2 to 3 min at 24 h postinoculation resulted in a reduction in excess of 5 log CFU/cm2 of Salmonella Poona and E. coli populations. Cantaloupes that were surface pasteurized and stored at 4°C for 21 days retained their firmness qualities and had no visible mold growth compared with the controls, which became soft and moldy. These results indicate that surface pasteurization will enhance the microbiological safety of cantaloupes and will extend the shelf life of this commodity as well. Storage of untreated inoculated cantaloupes at RT for 24 to 72 h postinoculation caused a significant (P < 0.05) increase in Salmonella Poona and E. coli populations compared with storage at 4°C. This indicates that cantaloupes should be refrigerated as soon as possible following harvest to suppress the growth of any possible contaminant on the rind.

Nutrient-limited yeast growth in Candida albicans: effect on yeast-mycelial transition

The yeast-mycelial transition in Candida albicans can be induced from yeast cells grown on minimal defined medium only in stationary phase. This study examined the inducibility of cultures in which growth was limited by the availability of the nutrients, glucose, NH4Cl, or galactose. The results showed that neither stationary phase nor cell cycle stage alone was a sufficient condition to support subsequent germ tube formation. In addition, final cell concentration alone was not a factor in inducibility. When a hundredfold decrease in growth was obtained by limiting any of the nutrients, a loss in inducibility was observed. However, the loss of inducibility differed with the limiting nutrient. Galactose, NH4Cl, and glucose-limited cultures showed respectively 15, 30, and 80% loss of inducibility. Thus the effect was associated with both carbon/energy and nitrogen-limited cells; however, glucose appeared to have a specific effect. These observations suggest that the metabolic state of the stationary phase yeast cell was an important factor in the subsequent ability to respond to conditions inducing germ tube formation.

Effect of Heat Treatments on Survival and Growth of a Psychrotroph and on Nitrogen Fractions in Milk1

Grade A raw milk which had initial psychrotrophic counts of less than 103/ml was inoculated with an antibiotic-resistant Pseudomonas sp. to a final cell concentration of 102, 104, or 106/ml. The inoculated milk was held at 4 C for 14 h and then exposed to the following time-temperature treatments: 72 C for 15 sec, 79 C for 15 sec, 88 C for 10 sec, and 95 C for < 5 sec. An uninoculated raw milk control was handled and analyzed along with inoculated samples. Aliquots of milk were analyzed for marked Pseudomonas sp., total psychrotrophic counts, numbers of Pseudomonas, and for distribution of nitrogen before and after each heat treatment and after storage of non-heat-treated raw milk and heat-treated samples for 7 and 14 days at 7 C. Psychrotrophic counts were significantly affected by heat treatment, initial cell inoculum, days stored, and plating media. Non-casein N, non-casein protein, total albumin, β-lactoglobulin, proteose-peptone, and globulin N were significantly decreased by heat treatment. Non-casein N, non-casein protein, β-lactoglobulin, and proteose-peptone were significantly increased by days of storage.