Data on the influence of temperature on the growth of Escherichia coli in a minimal medium containing glucose as the sole carbon source for the joint computation of growth yields and rates at each temperature from 27 to 45°C.

Temperature is a key factor influencing microbial growth rates and yields. In literature, the influence of temperature on growth is studied either on yields or rates but not both at the same time. Moreover, studies often report the influence of a specific set of temperatures using rich culture media containing complex ingredients (such as yeast extract) which chemical composition cannot be precisely specified. Here, we present a complete dataset for the growth of Escherichia coli K12 NCM3722 strain in a minimal medium containing glucose as the sole energy and carbon source for the computation of growth yields and rates at each temperature from 27 to 45°C. For this purpose, we monitored the growth of E. coli by automated optical density (OD) measurements in a thermostated microplate reader. At each temperature full OD curves were reported for 28 to 40 microbial cultures growing in parallel wells. Additionally, a correlation was established between OD values and the dry mass of E. coli cultures. For that, 21 dilutions were prepared from triplicate cultures and optical density was measured in parallel with the microplate reader (ODmicroplate) and a UV-Vis spectrophotometer (ODUV-vis) and correlated to duplicate dry biomass measurements. The correlation was used to compute growth yields in terms of dry biomass.

Chronic impact of sulfamethoxazole on the metabolic activity and composition of enriched nitrifying microbial culture.

This study investigated the chronic impact of sulfamethoxazole (SMX) on activated sludge sustaining an enriched nitrifying biomass. For this purpose, a laboratory scale fill and draw reactor was operated with 100 mg COD/L of peptone mixture and 50 mg N/L of ammonia at a sludge age of 15 days. Additionally, the biomass was exposed to a daily SMX dose of 50 mg/L once the reactor reached steady-state conditions. The reactor performance and microbial composition were monitored for 37 days with conventional parameters and molecular techniques based on the gene for ammonia monooxygenase subunit A (amoA) and the prokaryotic 16S rRNA gene. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene cloning analyses suggested a microbial community change concurrent with the addition of SMX. Specifically, quantitative polymerase chain reaction analyses (qPCR/RT-qPCR) revealed a significant reduction in the levels and activity of ammonia oxidizing bacteria (AOB). However, the acclimation period ended with high amoA mRNA levels and improved nitrification efficiency. Partial degradation of SMX by heterotrophic bacteria was also observed.

Modelling aerobic stabilization of domestic and industrial sludge using a multi-component biomass model.

The objective of the study was to investigate the achievable limits of aerobic sludge stabilization applied on waste-activated sludge generated in domestic, tannery, and pharmaceutical wastewater treatment plants. Stabilization study involved monitoring of conventional parameters and model evaluation of oxygen uptake rate and particulate components of waste sludge. Multi-component biomass approach was adopted based on death-regeneration mechanism. The results showed that sludge stabilization efficiency ranged between 25% and 30%, which was closely related to the fate of different particulate fractions of biomass, that is, viable biomass, hydrolysable particulates, and microbial metabolic products. Model calibration exercises yield in rate coefficient ranges of 0.18-0.32/day for biomass decay and 0.60-0.65/day for hydrolysis of non-biomass components. Degradation rates of particulate metabolic products were estimated as 0.035, 0.04, and 0.01/day for domestic, tannery, and pharmaceutical sludge, respectively. Relatively low degradation rates compared to conventional biological treatment processes confirmed reduced microbial activity in the course of aerobic stabilization.

Chronic impact of tetracycline on nitrification kinetics and the activity of enriched nitrifying microbial culture.

This study evaluated the chronic impact of tetracycline on biomass with enriched nitrifying community sustained in a lab-scale activated sludge system. For this purpose, a fill and draw reactor fed with 100 mg COD/L of peptone mixture and 50 mg N/L of ammonia was sustained at a sludge age of 15 days. At steady-state, the reactor operation was continued with a daily tetracycline dosing of 50 mg/L for more than 40 days, with periodic monitoring of the microbial composition, the nitrifying bacteria abundance, as well as the amoA and 16S rRNA gene activity, using molecular techniques. Changes in the kinetics of nitrification were quantified by modelling concentration profiles of major nitrogen fractions and oxygen uptake rate profiles derived from parallel batch experiments. Activated sludge modeling results indicated inhibitory impact of tetracycline on the growth of nitrifiers with a significant increase of the half saturation coefficients in corresponding rate equations. Tetracycline also inactivated biomass components of the enriched culture at a gradually increasing rate with time of exposure, leading to total collapse of nitrification. Molecular analyses revealed significant changes in the composition of the microbial community throughout the observation period. They also showed that continuous exposure to tetracycline inflicted significant reduction in amoA mRNA and 16S rRNA levels directly affecting nitrification. The chronic impact was much more pronounced on the ammonia oxidizing bacteria (AOB) community. These observations explained the basis of numerical changes identified in the growth kinetics of nitrifiers under stress conditions.

Acute impact of erythromycin and tetracycline on the kinetics of nitrification and organic carbon removal in mixed microbial culture.

The study evaluated acute impact of erythromycin and tetracycline on nitrification and organic carbon removal kinetics in mixed microbial culture. Acclimated biomass was obtained from a fill and draw reactor fed with peptone mixture selected as synthetic substrate and operated at a sludge age of 10 days. Acute inhibition was tested in batch reactors involving a control unit started solely with substrate and the others with additional doses of each antibiotic. Modeling indicated that both steps of nitrification were totally blocked by erythromycin. Tetracycline inhibited and retarded nitrification kinetics at 50 mg/L and stopped nitrite oxidation at 200 mg/L, leading to nitrite accumulation. Both antibiotics also affected organic carbon removal by inducing partial inactivation of the heterotrophic community in the culture, increased substrate storage and accelerated endogenous respiration, with a relatively slight impact on heterotrophic growth. Major inhibitory effect was on process stoichiometry, leading to partial utilization of organic substrate.

Is ammonification the rate limiting step for nitrification kinetics?

This study investigated relative magnitude of hydrolysis and ammonification by separate analysis of ammonia release and nitrification mechanisms. A peptone mixture was used as substrate in two parallel experiments seeded with nitrifying biomass conducted with and without nitrification inhibitor. Results were evaluated by means of model analysis of the ammonia and the oxygen uptake rate (OUR) profiles. A dual hydrolysis mechanism with maximum rate coefficients of 6.3 and 0.5/day characterized the peptone mixture and a kinetic balance was established for the ammonia release mechanism with a corresponding ammonification rate of 0.08 m(3)/g COD day. The experiments also showed a low soluble ammonia nitrogen generation that was rapidly depleted, confirming the existence of ammonification. These rate coefficients were verified using model calibration of the OUR profile related to simultaneous carbon removal and nitrification. Results indicated that ammonification would not be rate limiting for wastewaters such as domestic sewage, with lower hydrolysis kinetics.