The role of temperature and carbon dioxide climatic stress factors on the growth kinetics of Escherichia coli.

AIMS: The global level of carbon dioxide and temperature in the atmosphere is expected to increase, which may affect the survival of the stress-adapted bacteria. In this study, the effect of temperature and dissolved carbon dioxide on the growth rate of Escherichia coli-eGFP tagged strain was studied, thus assessing its response to induced environmental stress factors. METHODS AND RESULTS: A kinetic assay has been performed using a microplate reader with a spectrofluorometer to determine the specific growth rates. Polynomial models were developed to correlate the environmental conditions of temperature and carbon dioxide with Escherichia coli BL21 (DE3) growth in culture media and dairy by-products. At a temperature of 42°C, as the dissolved CO2 increased, a decrease in µmax by 0.76 h-1 was observed. In contrast, at 27°C, this increase led to an increase in µmax by 0.99 h-1. Moreover, a correction factor was added when applying the model to dairy whey samples. CONCLUSIONS: The application of this developed model can be considered a useful tool for predicting the growth of Escherichia coli using climate projections.

Investigation of assimilable organic carbon (AOC) in flemish drinking water.

The aim of the study was to investigate the drinking water supplied to majority of residents of Flanders in Belgium. Over 500 water samples were collected from different locations, after particular and complete treatment procedure to evaluate the efficiency of each treatment step in production of biologically stable drinking water. In this study assimilable organic carbon (AOC) was of our interest and was assumed as a parameter responsible for water biostability. The influence of seasons and temperature changes on AOC content was also taken into account. The AOC in most of the non-chlorinated product water of the studied treatment plants could not meet the biostability criteria of 10 mug/l, resulting in the mean AOC concentration of 50 microg/l. However, majority of the examined chlorinated water samples were consistent with proposed criteria of 50--100 microg/l for systems maintaining disinfectant residual. Here, mean AOC concentration of 72 microg/l was obtained. Granular activated carbon filtration was helpful in diminishing AOC content of drinking water; however, the nutrient removal was enhanced by biological process incorporated into water treatment (biological activated carbon filtration). Disinfection by means of chlorination and ozonation increased the water AOC concentration while the ultraviolet irradiation showed no impact on the AOC content. Examination of seasonal AOC variations showed similar fluctuations in six units with the highest values in summer and lowest in winter.

Investigation of microbially available phosphorus (MAP) in flemish drinking water.

Several researchers have reported phosphorus growth limitations of heterotrophic bacteria instead of main energy source--organic carbon. Usually this phenomenon was noticed in waters with high organic carbon content, where phosphorus concentration was deficient to maintain the growth on level suggested by high organic carbon amount. We analysed the microbially available phosphorus (MAP) and assimilable organic carbon (AOC) in several drinking waters in Flanders, Belgium. Our aim was the investigation whether organic carbon or phosphorus is the restricting nutrient in specific water and determination of the impact of some treatment processes on MAP content. We obtained a wide range of MAP concentrations being from 0.3 to 15.2 microg P-PO(4)/l in finished drinking water. In a treatment unit applying ozone, MAP was found to be the nutrient that limits bacterial growth instead of organic carbon. Moreover, ozone caused slight MAP decrease. Granular activated carbon (GAC) filtration was able to diminish further the MAP content significantly but not below a certain level. The biofilm monitor supplied with the MAP-limited water resulted in significantly lower biofilm formation rate (BFR) value than the same installation fed with AOC-limited water.