Bacterial Specific Growth Rates Research Articles

Bacterioplankton of the Western Part of the Kara Sea

Data on the structural and production characteristics of bacterioplankton in the western part of the Kara Sea at the beginning and in the middle of summer are presented. In the region of the St. Anna Trough slope, the average abundance of prokaryotes for the water column was (594–708) × 103 cells/ml (26.4–36.5 mgC/m3) in June and (247–517) × 103 cells/ml (12–28 mgC/m3) at the beginning of August. On the transect along Novaya Zemlya, the average abundance of bacterioplankton in the water column was (186–554) × 103 cells/mL (8.5–30 mgC/m3) within a week after the seasonal ice and (169–443) × 103 cells/mL (8–21 mgC/m3) in the midsummer. Bacterial specific growth rate did not exceed 1.28 day–1; its high values were observed in the upper warm water layer, above the halocline, and also at the near-bottom depths. At the beginning of summer, the production of bacterioplankton tended to decrease in the northeast direction. The distribution of prokaryotes abundance was determined by temperature and water saturation with oxygen, possibly as an indirect indicator of past phytoplankton “bloom”.

Development of a feed-forward control system for medium in shake-flask culture

Shake-flask culture is used in various applications and is one of the most widely used aerobic culture methods at the laboratory scale. Most shake-flask cultures used upstream of bioprocess development use a batch mode strategy, necessitating the expansion of culture conditions in upstream bioprocess development not limited to batch mode. Hence, the development of convenient small-scale fed-batch culture methods is necessary. The aim of this study was to develop a system that can provide a feed strategy for shaking cultures using an Erlenmeyer flask with a breathable culture stopper. The developed system comprises commercial products, is equipped with a sampling unit that does not interfere with the feeding strategy when collecting culture broth during shaking culture, and is applied to a shake-flask culture of Saccharomyces cerevisiae. The set values for bacterial yield and specific growth rate were fixed at 0.5 g-dry cell/g-D-glucose and 0.2 /h, respectively, whereas the measured values were observed to be 0.55 g-dry cell/g-D-glucose and 0.22 /h, respectively (batch mode: 0.22 g-dry cell/g-D-glucose and 0.45 /h, respectively). These results indicate that the developed system enables highly accurate feed-forward control of the feeding solution without changing the conventional components used in the shake-flask culture methods.

Unstructured kinetic models with time-averaged growth approach in the biodegradation of triclosan by activated sludge culture

The concentration of triclosan in wastewater is expected to rise dramatically as a consequence of the COVID-19 pandemic. A modeling analysis of the growth kinetics of microbial culture during triclosan degradation was necessary in order to establish effective wastewater treatment. The kinetic parameters are used by engineers to aid in the design and process control of biological processes. Studies were conducted using triclosan-acclimated culture to examine biomass growth and associated substrate degradation at different initial substrate concentrations (0.35–4.9 mg L−1) to this end. Substrate inhibition was calculated from experimental growth parameters using unstructured kinetic models. Unlike other model studies, a time-averaged specific bacterial growth rate in the log phase was considered for kinetic models in this study. Overestimation of the conventional log phase calculation for unstructured kinetic model constants was eliminated when the slowdown growth part of the log growth phase was taken into account. The Haldane Model was more accurate to fitting experimental data in an excellent manner. In this case, the time-averaged specific growth rate, saturation constant, and inhibition constant were 0.56 h−1, 12.77 mg L−1, 0.52 mg L−1, respectively. A yield coefficient of 0.404 mgX.mgS−1 was calculated. The critical triclosan concentration was 2.57 mg L−1. Wastewater treatment plants can be more sensitive to the value of the critical triclosan concentration. The value for time-averaged critical specific growth rate was 0.051 h−1. Pre-or post-treatment requirements can be estimated using time-averaged critical growth rate values as a benchmarking tool in biological treatment systems.

Viral shunt in tropical oligotrophic ocean.

Viruses cause massive bacterial mortality and thus modulate bacteria-governed carbon transfer and nutrient recycling at global scale. The viral shunt hypothesis states the crucial role of viral lysis in retaining microbial carbon into food web processes, while its applicability to nature has not been well identified for over two decades. Here, we conducted nine diel surveys in the tropical South China Sea and suggested that the time scale adopted in sampling and system trophic status determine the “visibility” of the viral shunt in the field. Specifically, viral abundance (VA), bacterial biomass (BB), and bacterial specific growth rate (SGR) varied synchronously and presented the significant VA-BB and VA-SGR linkages at an hourly scale, which reveals direct interactions between viruses and their hosts. The differential responses of the viral shunt to temperature, i.e., looser VA-SGR coupling in warm and tighter VA-SGR coupling in cold environments, imply an altered carbon cycling in tropical oceans under climatic warming.

A Predictive Growth Model for Pro-technological and Probiotic Lacticaseibacillus paracasei Strains Fermenting White Cabbage.

Bacterial strains belonging to Lacticaseibacillus paracasei species are generally used as starters in food fermentations and/or as probiotics. In the current study, the growth cardinal parameters of four L. paracasei strains (IMPC2.1, IMPC4.1, P40 and P101), isolated from table olives or human source, were determined. Strains were grown in liquid medium and incubated at several temperatures (10 values from 5.5°C–40°C) and pH (15 values from 3.2 to 9.1) along the growth range. The cardinal temperature model was used to describe temperature effects on the maximum specific growth rate of L. paracasei whereas new equations were developed for the effect of pH. The estimated Tmin values ranged between −0.97°C and 1.95°C and were lower than 0°C for strains IMPC4.1 and P101. Strain P40 was able to grow in the most restricted range of temperature (from 1.95°C to 37.46°C), while strain IMPC4.1 was estimated to survive at extreme conditions showing the lowest pHmin. Maximum specific growth rates of L. paracasei IMPC2.1 in white cabbage (Brassica oleracea var. capitata) were used to calculate the correction factor (Cf) defined as the bias between the bacterial maximum specific growth rate in broth and in the food matrix. A simple bi-linear model was also developed for the effect of temperature on the maximum population density reached in white cabbage. This information was further used to simulate the growth of L. paracasei strains in cabbage and predict the time to reach the targeted probiotic level (7 log10 CFU/g) using in silico simulations. This study demonstrates the potential of the predictive microbiology to predict the growth of beneficial and pro-technological strains in foods in order to optimize the fermentative process.

Influence of the Carbon and Nitrogen Sources on Diabolican Production by the Marine Vibrio diabolicus Strain CNCM I-1629.

Recent advances in glycobiotechnology show that bacterial exopolysaccharides (EPS) presenting glycosaminoglycan (GAG)-like properties can provide a valuable source of bio-active macromolecules for industrial applications. The HE800 EPS, named diabolican, is a marine-derived anionic high-molecular-weight polysaccharide produced by Vibrio diabolicus CNCM I-1629 which displays original structural features close to those of hyaluronic acid. We investigated the impact of carbon and nitrogen substrates on both Vibrio diabolicus growth and diabolican production. Both substrates were screened by a one-factor-at-a-time method, and experimental designs were used to study the effect of glucose, mannitol, and ammonium acetate various concentrations. Results showed that the medium composition affected not only the bacterium growth and EPS yield, but also the EPS molecular weight (MW). EPS yields of 563 and 330 mg L−1 were obtained in the presence of 69.3 g L−1 glucose and 24.6 g L−1 mannitol, respectively, both for 116.6 mM ammonium acetate. MW was the highest, with 69.3 g L−1 glucose and 101.9 mM ammonium acetate (2.3 × 106 g mol−1). In parallel, the bacterial maximum specific growth rate was higher when both carbon and nitrogen substrate concentrations were low. This work paves the way for the optimization of marine exopolysaccharide production of great interest in the fields of human health and cosmetics.

Mathematical Modeling of the growth of Acinetobacter baumannii YNWH 226 on Azo dye Congo red

Industrial effluents (Azo dyes) are brightly coloured, making their disposal into receiving waters undesirable not only because many Azo dyes and their breakdown products are toxic to aquatic life and mutagenic to humans, but also because many Azo dyes and their breakdown products are harmful to aquatic life due to the presence of aromatics and metals, chlorides, and other chemicals. Various kinetic models, including modified Gompertz, Baranyi-Roberts, modified Richards, Von Bertalanffy, modified Logistics, modified Schnute, Buchanan three-phase, and the most recently presented Huang, were used in this study. Based on statistical tests, the modified Schnute model provided the best fit, with the lowest values for RMSE and corrected Akaike Information Criteria (AICc), the greatest value for adjusted R2, and the closest to unity for both Accuracy and Bias Factor. The Modified Schnute parameters such as λ (lag time), µmax (maximum specific bacterial growth rate) and curve fitting parameters α and β (Constant), were found to be -4.39 (95% confidence interval of -77.58 to 68.79), 57.00 (95% confidence interval of -2854.30 to 2968.30), 0.78 (95% confidence interval of -0.34 to 1.89) and 0.96 (95% confidence interval of -0.85 to 2.78, respectively.

Simplified Approach to Predict Food Safety through the Maximum Specific Bacterial Growth Rate as Function of Extrinsic and Intrinsic Parameters

Currently, we assist the emergence of sensors and low-cost information and communication technologies applied to food products, in order to improve food safety and quality along the food chain. Thus, it is relevant to implement predictive mathematical modeling tools in order to predict changes in the food quality and allow decision-making for expiration dates. To perform that, the Baranyi and Roberts model and the online tool Combined Database for Predictive Microbiology (Combase) were used to determine the factors that define the growth of different bacteria. These factors applied to the equation that determines the maximum specific growth rate establish a relation between the bacterial growth and the intrinsic and extrinsic factors that define the bacteria environment. These models may be programmed in low-cost wireless biochemical sensor devices applied to packaging and food supply chains to promote food safety and quality through real time traceability.

A Computational Approach to Incorporate Metabolite Inhibition in the Growth Kinetics of Indigenous Bacterial Strain Bacillus subtilis MN372379 in the Treatment of Wastewater Containing Congo Red Dye.

A rigorous knowledge of the bacterial growth kinetics is essential for the scaling-up and optimization of biodegradation process conditions in a bioreactor. Although a great deal of literature is available on the modeling of bacterial growth kinetics considering the inhibition at high substrate-loading, the inhibition caused by toxic metabolic byproducts was not accounted in the bacterial growth kinetics. This work primarily aimed at developing a parametric bacterial growth model to account for metabolite inhibition, indicated by a decelerating log-phase growth, which was rarely discussed in the previous studies. An efficient azo-dye degrading bacterium (Bacillus subtilis MN372379) was isolated from the sludge-waste nearby a carpet-dyeing unit. The isolated bacterial strain was used to decolorize the simulated wastewater containing Congo red dye. This study proposed a computational approach to calculate specific bacterial growth rate time-averaged over the entire sigmoidal log phase (including the decelerating phase) for incorporating the effect of metabolite-inhibition, in contrast to the conventional studies where only the initial part (accelerating) of log phase was considered. The nature of metabolite inhibition was also determined and found to be non-competitive. Next, the computed time-averaged specific bacterial growth rate was incorporated into three substrate inhibition models to account for both, the metabolite and substrate inhibitions, and subsequently their kinetic parameters were also determined. Finally, the initial dye concentration and inoculum size were optimized to yield maximum dye utilization rate. This study paves the way for predicting bacterial growth kinetic with improved accuracy to enable a better optimization of bioreactors at the industrial scale.

Modelling the Growth of Enterobacter sp. on Polyethylene

Although standard, the use of linearization techniques using natural logarithm transformation is erroneous and can only give an estimated value for the measured parameter; the specific growth rate. For the first time, in this paper, we present different kinetic models such as Von Bertalanffy, Baranyi-Roberts, modified Schnute, modified Richards, modified Gompertz, modified Logistics and most recent Huang were employed to obtain values for the above constants or parameters from Enterobacter sp. growth on polyethylene. Huang model was found to be the best model with the highest adjusted R2 value and lowest RMSE value. The Accuracy and Bias Factors values were close to unity (1.0). The Huang parameters such as Ymax (bacterial growth upper asymptote), λ (lag time), µmax (maximum specific bacterial growth rate) and A or Y0 (bacterial growth lower asymptote) were found to be 1.367 (95% confidence interval of 1.322 - 1.412), 2.683 (95% confidence interval of 2.030 - 3.337), 0.322 (95% confidence interval of 0.252 - 0.392) and 0.324 (95% confidence interval of 0.278 - 0.370).

Growth Mathematical Modelling of the Effect of Cyanide on Pseudomonas putida (Naun-16)

Gold mining companies have been known to use cyanide to extract gold from minerals. The indiscriminate use of cyanide presents a major issue in the environment. The used of linearisation methods using natural logarithm transformation is inaccurate, even though is standard and can just give an estimated value for the sole parameter measured; the specific growth rate. In this study, various cyanide concentrations ranging from 0 - 350 mg/L was used. Seven different mathematical models such as such as modified Logistics, modified Gompertz, modified Richards, modified Schnute, Baranyi-Roberts, Von Bertalanffy and most recent Huang were used to get values for the above constants or parameters from bacterial growth Pseudomonas putida on cyanide. The best model was found to be modified Logistics with the lowest AICc and RMSE value. The modified Logistics parameters such as Ymax (bacterial growth upper asymptote), λ (lag time), µmax (maximum specific bacterial growth rate) and A or Y0 (bacterial growth lower asymptote) were found to be 2.41 (95% confidence interval of 2.37 - 2.45), -3.16 (95% confidence interval of -4.64 to -1.68) and 0.12 (95% confidence interval of 0.11 to 0.13). This is the first report of growth mathematical modelling of the effect of cyanide on Pseudomonas Putida (Naun-16).

Diesel degrading bacterial endophytes with plant growth promoting potential isolated from a petroleum storage facility.

Thirteen (13) endophytic bacterial strains were isolated from Echinochloa crus-galli (Cockspur grass) and Cynodon dactylon (Bermuda grass) growing in an oil-contaminated site at a petroleum storage and transportation facility. Of the 13 strains assessed for their potential to degrade monoaromatic compounds (phenol, toluene, and xylene) and diesel and for their plant growth promoting (PGP) ability (phosphate solubilization, siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production), isolate J10 (identified as Pseudomonas sp. by 16S rRNA gene sequencing) was found to the best diesel biodegrader with the best PGP traits. The Monod model used for Pseudomonas sp. J10 growth kinetics on diesel fuel as the sole carbon source showed that the maximum specific bacterial growth rate was 0.0644h- 1 and the half velocity constant (K s ) was estimated as 4570mg L- 1. The overall growth yield coefficient and apparent growth yield were determined to be 0.271g h- 1 and 0.127g cells/g substrate, respectively. Pseudomonas sp. J10 removed 69% diesel in four days as determined by gas chromatographic (GC) analysis. These findings could assist in developing an endophyte assisted efficient diesel biodegradation system using Pseudomonas sp. J10 isolated from Echinochloa crus-galli.

Mathematical Modelling of the Growth of Caulobacter crescentus on Caffeine

Caffeine is a purine alkaloid naturally found in many species of plant and can be degraded by bacteria. Prolong caffeine consumption is well-known to have serious adverse effects. The used of linearization technique using natural logarithm transformation, though standard, is erroneous and can just give an estimated value for the sole parameter measured; the specific growth rate. In this paper, for the first time we present different kinetics models such as Von Bertalanffy, Baranyi-Roberts, modified Schnute, modified Richards, modified Gompertz, modified Logistics and most recent Huang were used to get values for the above constants or parameters from Caulobacter crescentus bacterium growth on caffeine. Huang model was found to be the best model with the highest adjusted R2 value with the lowest RMSE value. The Accuracy and Bias Factors values were close to unity (1.0). The Huang parameters such as Ymax (bacterial growth upper asymptote), λ (lag time), µmax (maximum specific bacterial growth rate) and A or Y0 (bacterial growth lower asymptote) were found to be 1.367 (95% confidence interval of 1.322 - 1.412), 2.683 (95% confidence interval of 2.030 - 3.337), 0.322 (95% confidence interval of 0.252 - 0.392) and 0.324 (95% confidence interval of 0.278 - 0.370).

Mathematical Modelling of the Growth Curve of Vibrio sp. Isolate MZ Grown in Seawater Medium

Pollution in the environment is deteriorating the ecology due to human activities in a large array of industrial and agricultural sectors. Bioassay of polluted waters using bioluminescent bacterium has been touted as one of the most economical, rapid and sensitive tests. The growth of the bacterium on seawater medium exhibited a typical sigmoidal profile. To extract important growth parameters useful for further modelling exercise, various primary growth models were utilized in this study such as Modified Logistic, modified Gompertz, modified Richards, modified Schnute, Baranyi-Roberts, von Bertalanffy, Huang and the Buchanan three-phase model. The best performance was Huang model with the lowest value for RMSE, AICc and the highest value for adjusted R2. The AF and BF values were also excellent for the model with their values were the closest to 1.0. The Huang parameters, which include A or Y0 (bacterial growth lower asymptote), m (maximum specific bacterial growth rate),  (lag time) and Ymax (bacterial growth upper asymptote) were 7.866 (95% confidence interval of 7.850 to 7.883), 0.329 (95% confidence interval of 0.299 to 0.359), 1.543 (95% confidence interval of 1.303 to 1.784) and 8.511 (95% confidence interval of 0.299 to 0.359).

Relationship between Escherichia coli growth rate and bacterial susceptibility to ciprofloxacin.

The effect of Escherichia coli growth rate on its susceptibility to ciprofloxacin was investigated using bacteria grown on different carbon sources and harboring mutations in genes encoding tricarboxylic acid cycle enzymes. A 1-h treatment of the wild type (wt) grown on glucose, succinate, malate, α-ketoglutarate or acetate with 0.3 μg ml-1 ciprofloxacin decreased the number of surviving cells (CFU ml-1), 560, 110, 74, 62 and 5 times, respectively. Among the mutants tested, sucB strain, which grew 1.75 times slower than wt, was 7.4-fold more tolerant to 0.3 μg ml-1 of ciprofloxacin than wt. Strong inverse correlations between log(CFU ml-1) after 1-h exposure to 0.3 and 3.0 μg ml-1 ciprofloxacin and the specific growth rate prior to antibiotic treatment (r = - 0.93 and -0.96, respectively) were observed. Data from the current and previous studies on the inhibitory effect of ciprofloxacin on cultures exhibiting a wide range of growth rates (0.01-1.3 h-1) were collated. Statistical analysis revealed a significant inverse correlation between log(CFU ml-1) after exposure to 3.0 μg ml-1 of ciprofloxacin and the specific bacterial growth rate prior to antibiotic exposure (r = -0.92). These data may be used in a design of antibiotic treatment protocols.

Aerobic degradation and metabolite identification of the N-heterocyclic indole by the Pseudomonas putida strain mpky-1 isolated from subtropical mangrove sediment

Aerobic biodegradation and metabolite identification of indole by the Pseudomonas putida strain mpky-1 isolated from coastal sediment of the Inner Deep Bay of Hong Kong was investigated in this study. This strain had 99.1% similarity with P. putida known. The biochemical degradation pathway of indole involved an initial hydroxylation reaction at the C-2 position to form oxindole followed by a second hydroxylation at the C-3 position to isatin prior to the cleavage of the 5-member carbon ring. This bacterium grew better at 22oC though it was capable of growth at low temperature (15oC in this study) with a longer lag phase. Both the bacterial specific growth rate and the biodegradation rate increased from 0.0035 hr-1 to 0.0249 hr-1 and from 15oC to 30oC, respectively. P. putida mpky-1 grew quicker at pH 6.4 (specific growth rate, 0.0115 hr-1) than pH 7.4 (specific growth rate, 0.0066 hr-1) and pH 8.4 (specific growth rate, 0.036 hr-1) although the lag time of bacterial growth at pH 7.4 and pH 8.4 (15.01 hr and 15.00 hr, respectively) was very similar. The decrease in bacterial growth rate was observed when salinity increased from 5‰ to 30‰. P. putida mpky-1 may adapt to the Mai Po and Inner Deep Bay and degrade indole due to the polluted condition.

Comparative effects of Ni(II) and Cu(II) ions and their combinations on redox potential and hydrogen photoproduction by Rhodobacter sphaeroides

The aim of the present work was the study of comparative effects of Cu(II) and Ni(II) and their mixture on growth, redox potential, hydrogen (H2) yield and ATPase activity in phototrophic purple bacteria R. sphaeroides MDC6522 from Jermuk mineral spring in Armenia. It was ascertained, that Cu2+ and Ni2+ have different effects on bacterial specific growth rate: in the presence of 5μM Cu2+ growth rate was ~3.2-fold lower in comparison with control (no addition), and increased ~1.5-fold in medium with 5μM Ni2+. These changes may be resulted by action of the ions on redox potential (Eh). Low concentrations of Ni2+ had an enhancing effect on the Eh drop and H2 production. The increase of concentration from 1 to 5μM enhanced the stimulatory effect of Ni2+. H2 yield in R. sphaeroides (72h of growth) was enhanced ~3-fold with 5μM Ni2+, whereas in the presence of 5μM Cu2+ H2 yield was ~1.2 fold lower in comparison with control. Cu2++Ni2+ combinations effects were differed from the effect when ions used separately. When Cu2+ and Ni2+ were added together, the Ni2+ stimulatory effect disappeared, which indicated that heavy metal ions mixture may have different action mechanisms. Moreover, N,N′-dicyclohexylcarbodiimide-sensitive ATPase activity of R. sphaeroides membrane vesicles has been increased in the presence of both ions, but in the presence of Сu2+ the influence was feebly marked in comparison with Ni2+. The results suggest an interaction between these ions and the FOF1-ATPase. Thus, the results obtained point out discrimination between Cu2+ and Ni2+ and their combinations effects and reveal new regulatory pathways to enhance H2 yield in R. sphaeroides.

Bacterial production in subarctic peatland lakes enriched by thawing permafrost

Abstract. Peatlands extend over vast areas of the northern landscape. Within some of these areas, lakes and ponds are changing in size as a result of permafrost thawing and erosion, resulting in mobilization of the carbon-rich peatland soils. Our aims in the present study were to characterize the particle, carbon and nutrient regime of a set of thermokarst (thaw) lakes and their adjacent peatland permafrost soils in a rapidly degrading landscape in subarctic Québec, Canada, and by way of fluorescence microscopy, flow cytometry, production measurements and an in situ enrichment experiment, determine the bacterial characteristics of these waters relative to other thaw lakes and rock-basin lakes in the region. The soil active layer in a degrading palsa (peatland permafrost mound) adjacent to one of the lakes contained an elevated carbon content (51 % of dry weight), high C : N ratios (17 : 1 by mass), and large stocks of other elements including N (3 % of dry weight), Fe (0.6 %), S (0.5 %), Ca (0.5 %) and P (0.05 %). Two permafrost cores were obtained to a depth of 2.77 m in the palsa, and computerized tomography scans of the cores confirmed that they contained high concentrations (> 80 %) of ice. Upon thawing, the cores released nitrate and dissolved organic carbon (from all core depths sampled), and soluble reactive phosphorus (from bottom depths), at concentrations well above those in the adjacent lake waters. The active layer soil showed a range of particle sizes with a peak at 229 µm, and this was similar to the distribution of particles in the upper permafrost cores. The particle spectrum for the lake water overlapped with those for the soil, but extended to larger (surface water) or finer (bottom water) particles. On average, more than 50 % of the bacterial cells and bacterial production was associated with particles > 3 µm. This relatively low contribution of free-living cells (operationally defined as the < 1 µm fraction) to bacterial production was a general feature of all of the northern lakes sampled, including other thaw lakes and shallow rock-basin lakes (average ± SE of 25 ± 6 %). However, a distinguishing feature of the peatland thaw lakes was significantly higher bacterial specific growth rates, which averaged 4 to 7 times higher values than in the other lake types. The in situ enrichment experiment showed no difference between organic carbon or phosphorus enrichment treatments at day 5 relative to the control, however there was an apparent increase in bacterial growth rates between days 1 and 5 in the soil and the carbon plus phosphorus enrichments. Collectively these results indicate that particles, nutrients and carbon are released by degrading permafrost peatland soils into their associated thermokarst lakes, creating favorable conditions for production by particle-based as well as free-living aquatic bacterial communities. The reduced bacterial concentrations despite high cellular growth rates imply that there is control of their population size by loss-related factors such as grazing and viral lysis.

Optimizing strategy for Escherichia coli growth and hydrogen production during glycerol fermentation in batch culture: Effects of some heavy metal ions and their mixtures

Hydrogen (H2) is well-known effective, ecologically clean and renewable fuel. Bacterial H2 production is a promising one and its use in industrial level is expected to increase in the nearest future to establish sustainable and renewable energy source. Escherichia coli wild type BW25113 growth yield was shown to be stimulated 1.3–1.5-fold by nickel (Ni2+), iron (Fe2+, Fe3+) ions and by some metal ion mixtures: Ni2++Fe2+ + molybdenum (Mo6+), Ni2++Fe3+, Ni2++Fe2+ and Mo6++Fe3+ in low concentrations (<0.05mM) stimulated the growth during glycerol (10gL−1) fermentation up to stationary phase at pH 6.5; Ni2++Fe2+ mixture showed the maximal effect. However, the same concentrations of these metals and their mixtures had no effects or slightly inhibited bacterial specific growth rate: it was suppressed ∼1.2-fold upon Ni2+, Fe3+, Mo6+ and Ni2++Mo6+ mixture supplementation. H2 production by E. coli from glycerol was observed with the yield of 0.75±0.02mmolL−1. Moreover, H2 yield was markedly stimulated 1.7–3-fold in the presence of Ni2++Fe3+, Ni2++Fe3++Mo6+ and Fe3++Mo6+ mixtures, but not sole metals: maximal stimulation was established by Fe3++Mo6+ mixture with the concentrations of 0.05mM and 0.02mM, respectively. While copper (Cu+, Cu2+) ions in low concentration (0.1mM) had H2 production suppressing effect. The results point out that some heavy metal ions and their mixtures can stimulate E. coli growth, as well as enhance bio-hydrogen production. Discrimination between Fe2+ and Fe3+ was important for H2 production. Some interaction of Ni2+ with Fe2+ was suggested to be effective factor increasing bacterial biomass and determining activity of H2 producing hydrogenases together with Fe3+. Mo6+ was significant for H2 production. The results obtained were important to develop H2 production biotechnology using glycerol as cheap substrate and optimizing the technological conditions by some heavy metals and their mixtures at low concentrations.

Coupling Between Heterotrophic Nanoflagellates and Bacteria in Fresh Waters: Does Latitude Make a Difference?

Recent studies reported comparatively lower heterotrophic bacteria (HB) abundances in tropical regions, indicating that factors involved in bacterial losses could be more relevant in the tropics. Heterotrophic nanoflagellates (HNF) are considered the main predators of HB in aquatic ecosystems, and one should expect higher abundances in the tropics because of differences in the food web configuration (absence of large daphnids). However, there are no comprehensive studies comparing HB and HNF abundances in a latitudinal gradient. We hypothesized that HB abundance would be lower in the tropics because HNF abundance would be higher, resulting in a tighter HNF–HB coupling. To test this hypothesis, we compiled a large dataset of HB and HNF abundances from tropical and temperate freshwater environments. We found that both HB and HNF abundances were lower in the tropical region, and that HNF-HB coupling does not differ between temperate and tropical regions. The lower HNF abundance and lack of coupling may be explained by a strong top-down control on HNF and/or their herbivory preference. Besides, no relationship was found between bacterial specific growth rate and either chlorophyll-a and HB abundance, indicating that bacterial losses may have an important role in tropical freshwaters. Thus, we found that HNF is likely not the main controllers of HB abundance, and that grazing by ciliates and cladocerans, together with the physiological effects of higher temperatures, may explain the high bacterial loss rates in the tropics.