Decrease In Specific Growth Rate Research Articles

A simple microbial fuel cell model for improvement of biomedical device powering times.

This study describes a Matlab based Microbial Fuel Cell (MFC) model for a suspended microbial population, in the anode chamber for the use of the MFC in powering biomedical devices. The model contains three main sections including microbial growth, microbial chemical uptake and secretion and electrochemical modeling. The microbial growth portion is based on a Continuously Stirred Tank Reactor (CSTR) model for the microbial growth with substrate and electron acceptors. Microbial stoichiometry is used to determine chemical concentrations and their rates of change and transfer within the MFC. These parameters are then used in the electrochemical modeling for calculating current, voltage and power. The model was tested for typically exhibited MFC characteristics including increased electrode distances and surface areas, overpotentials and operating temperatures. Implantable biomedical devices require long term powering which is the main objective for MFCs. Towards this end, our model was tested with different initial substrate and electron acceptor concentrations, revealing a four-fold increase in concentrations decreased the power output time by 50%. Additionally, the model also predicts that for a 35.7% decrease in specific growth rate, a 50% increase in power longevity is possible.

Differential Effect of Culture Temperature and Specific Growth Rate on CHO Cell Behavior in Chemostat Culture

Mild hypothermia condition in mammalian cell culture technology has been one of the main focuses of research for the development of breeding strategies to maximize productivity of these production systems. Despite the large number of studies that show positive effects of mild hypothermia on specific productivity of r-proteins, no experimental approach has addressed the indirect effect of lower temperatures on specific cell growth rate, nor how this condition possibly affects less specific productivity of r-proteins. To separately analyze the effects of mild hypothermia and specific growth rate on CHO cell metabolism and recombinant human tissue plasminogen activator productivity as a model system, high dilution rate (0.017 h−1) and low dilution rate (0.012 h−1) at two cultivation temperatures (37 and 33°C) were evaluated using chemostat culture. The results showed a positive effect on the specific productivity of r-protein with decreasing specific growth rate at 33°C. Differential effect was achieved by mild hypothermia on the specific productivity of r-protein, contrary to the evidence reported in batch culture. Interestingly, reduction of metabolism could not be associated with a decrease in culture temperature, but rather with a decrease in specific growth rate.

Comparative effects of dietary supplementation with maggot meal and soybean meal in gibel carp (Carassius auratus gibelio) and darkbarbel catfish (Pelteobagrus vachelli): growth performance and antioxidant responses

A 6-week growth trial was conducted to investigate the effect of dietary supplementation with maggot meal (MGM) and soybean meal (SBM) on the growth performance and antioxidant responses of gibel carp (GC) and darkbarbel catfish (DC). The basal diet was formulated to contain 114 g kg−1 fish meal (FM) and 200 g kg−1 SBM. The basal diet was supplemented with either 280 g kg−1 FM (Control), 390 g kg−1 MGM or 450 g kg−1 SBM to obtain three isonitrogenous (crude protein: 380 g kg−1) and isocaloric (gross energy: 16 kJ g−1) diets. For GC, a significant decrease in specific growth rate (SGR) was only observed in fish fed the SBM diet compared with the control (P < 0.05). Principal components analysis (PCA) of GC showed a higher similarity in antioxidant response to dietary supplementation with MGM and SBM proteins between liver and intestine, but the DC did not. The present results suggest that supplementing 390 g kg−1 MGM protein to basal diet cause an enhancement of the antioxidant capacity in GC, but supplementing 390 g kg−1 MGM and 450 g kg−1 SBM proteins to basal diets resulted in a significant attenuation of the antioxidant capacity in DC.

Responses of crucian carp Carassius auratus to long-term exposure to nitrite and low dissolved oxygen levels

Both nitrite (NO 2 –N) and dissolved oxygen (DO) are key water quality factors and can impact on aquatic animals' health. In this study, juvenile crucian carp Carassius auratus were exposed to different concentrations of NO 2 –N (0, 2.5, and 5 mg L −1 ) and DO (2 and 6 mg L −1 ) for 30 days. Results showed that under low DO conditions there was a decrease in specific growth rate, feeding rate, food conversion efficiency, and protein efficiency ratio. Red blood cell count (RBC) increased significantly with decreasing DO; three-way ANOVA indicated that there was a statistically significant interaction between DO and NO 2 –N on RBC. Hemoglobin content of fish exposed to low DO levels was significantly higher than that in the normal DO. Changes in the enzymatic (SOD and CAT) and non-enzymatic (GSH) antioxidants in fish liver and blood exhibited oxidative stress occurred under the conditions of low DO and high NO 2 –N. ► Under low dissolved oxygen conditions there was a decrease in growth and feeding. ► Red blood cell count increased significantly with decreasing dissolved oxygen. ► There was a significant interaction between dissolved oxygen and nitrite on RBC. ► Hemoglobin content increased significantly with decreasing dissolved oxygen. ► Oxidative stress occurred under low dissolved oxygen and high nitrite.

Responses of juvenile sea bass, Dicentrarchus labrax, exposed to acute concentrations of crude oil, as assessed by molecular and physiological biomarkers

In the present study, juvenile sea bass were exposed for 48 and 96h to an Arabian light crude oil and their responses were assessed at the molecular and physiological levels. The aim of the study was therefore to assess (i) the short term effects of crude oil exposure by the measurement of several molecular biomarkers, (ii) the consequences of this short term exposure on fish health by using growth and condition indices measured after a decontamination period of 28 and 26d in seawater. Hydrocarbon petroleum concentrations was monitored during the 96h experiments and an increase of PAH concentrations were found in fish following both exposure times. An 7-ethoxyresorufin-O-deethylase (EROD) induction was observed after 48h of exposure, while a significant decrease in the sea bass specific growth rate in length and for the RNA:DNA ratio was observed 28d after that exposure ceased. The EROD induction doubled after the 96h exposure, and a significant increase in GST activities was observed. A significant decrease in the specific growth rates, the otolith recent growth, the RNA:DNA ratio and the Fulton’s K condition index were then observed in sea bass 26d after the 96h exposure to mechanically dispersed crude oil compared to the control. The present study shows that growth and condition indices can prove useful in assessing fish health status following an oil spill. Their complementary analysis with sensitive molecular biomarkers as EROD could improve the determination of oil spill impact on fish populations.

Effect of oxygen concentration on the growth of Nannochloropsis sp. at low light intensity

In large-scale microalgal production in tubular photobioreactors, the build-up of O2 along the tubes is one of the major bottlenecks to obtain high productivities. Oxygen inhibits the growth, since it competes with carbon dioxide for the Rubisco enzyme involved in the CO2 fixation to generate biomass. The effect of oxygen on growth of Nannochloropsis sp. was experimentally determined in a fully controlled flat-panel photobioreactor operated in turbidostat mode using an incident photon flux density of 100 μmol photons m−2 s−1 and with only the oxygen concentration as variable parameter. The dissolved oxygen concentration was varied from 20 to 250% air saturation. Results showed that there was no clear effect of oxygen concentration on specific growth rate (mean of 0.48 ± 0.40 day−1) upon increasing the oxygen concentration from 20% to 75% air saturation. Upon further increasing the oxygen concentration, however, a linear decrease in specific growth rate was observed, ranging from 0.48 ± 0.40 day−1 at a dissolved oxygen concentration of 75% air saturation to 0.18 ± 0.01 day−1 at 250% air saturation. In vitro data on isolated Rubisco were used to predict the quantum yield at different oxygen concentrations in the medium. The predicted decrease in quantum yield matches well with the observed decrease that was measured in vivo. These results indicate that the effect of oxygen on growth of Nannochloropsis sp. at low light intensity is only due to competitive inhibition of the Rubisco enzyme. At these sub-saturating light conditions, the presence of high concentrations of oxygen in the medium induced slightly higher carotenoid content, but the increased levels of this protective antioxidant did not diminish the growth-inhibiting effects of oxygen on the Rubisco.

Cloning and Expression of α-Amylase Gene in Escherichia coli: Effect on Specific Oxygen Uptake Rate and Host Cell Morphology during Batch Fermentation

Cloning and expression of any heterologous gene product always impart metabolic load on the recombinant host for utilization of its metabolites that results in variations in cellular physiology. An understanding of such stress is important for robust process design and scale-up. In the present communication, an attempt has been made to explain the metabolic load imposed on the recombinant strain of Escherichia coli BL21(DE3) owing to over-expression of amyE gene, using different expression vectors of varying size. Current studies show that metabolic quotient or specific oxygen uptake rate (SOUR) of different recombinant hosts increases with an increase in vector size, showing correlation between vector size and cellular metabolic load. Further increase in SOUR on protein expression shows even higher metabolic load for protein expression than plasmid maintenance. Increase in bacterial size and decrease in specific growth rate on transformation and recombinant protein expression are cellular responses to additional metabolic load.

Effect of stocking density on growth and serum concentrations of thyroid hormones and cortisol in Amur sturgeon, Acipenser schrenckii

This study investigated the effects of different stocking densities on growth and serum concentrations of thyroid hormones and cortisol in Amur sturgeon, Acipenser schrenckii. Fish were reared at low, medium, and high stocking densities (initial experimental densities were 0.30, 0.75, and 1.78 kg m(-2), respectively) for 70 days. The results showed that high stocking density had negative effects on growth and feeding efficiency, and altered serum levels of thyroid hormones and cortisol in Amur sturgeon. A significant decrease in specific growth rate was observed as stocking density was increased. The feeding rate decreased significantly in the medium and high density groups, indicating that high stocking density reduced the food consumption of sturgeon. Food conversion ratio increased with increasing stocking density, suggesting that high stocking density might inhibit fish growth through decreasing food conversion efficiency. Serum concentrations of total triiodothyronine, free thyroxine, and free triiodothyronine were inversely related to stocking densities, whereas serum total thyroxine level of sturgeon stocked at different densities remained stable. Also, higher stocking density resulted in an elevation of serum cortisol level, indicating that the sturgeon stocked at the higher density experienced density-dependent physiological stress. These results suggest growth suppression caused by high stocking density might be related to both crowding stress and the declines in peripheral circulating levels of thyroid hormones, as well as associated with the reductions in both food consumption and food conversion efficiency.

Survival and growth of Mud crab, Scylla serrata, juveniles subjected to removal or trimming of chelipeds

The effects of removing or trimming the chelipeds at various molt stages on regeneration, molt interval (MI) and specific growth rate (SGR) were determined in mud crab Scylla serrata. These strategies in combination with provision of shelters and food were tested in relation to survival and growth. Hatchery-reared S. serrata juveniles (1.3–2.2 g body weight) in the postmolt, intermolt, and premolt stages were subjected to autotomy of two chelipeds, and trimming of dactylus and pollex. Intact crabs served as the control group. Interval from stocking to first molt was significantly longer in crabs autotomized at intermolt or premolt than in trimmed or intact crabs, but was similar to intact crabs when autotomy was done at postmolt. However, MI from first to second molts was longer compared to intact crabs when chelipeds were removed or trimmed at premolt. After the first molt, autotomy and not trimming caused significant decrease in SGR. The SGRs at the end of the test were similar to intact crabs (postmolt: 7.90 ± 0.39, intermolt: 5.64 ± 0.50) when trimming of chelipeds was done at postmolt (8.01 ± 0.75) or intermolt (4.38 ± 0.40). However, SGR was lower when premolt crabs were subjected to autotomy (4.11 ± 0.67) and trimming (5.29 ± 1.40) than when chelipeds were intact (9.45 ± 0.47). A two-factor experiment was conducted in the second phase where intermolt crabs with autotomized or trimmed chelipeds (factor A) were either fed or starved but provided with shelters or fed but without shelters (factor B). After 10 days, higher survival was obtained in crabs with autotomized (95.55 ± 2.94%) or trimmed chelipeds (93.33 ± 3.33%) than in intact crabs (73.33 ± 6.67%). Survival was not affected by factor B, but higher final mean body weights were attained in fed crabs with (0.78 ± 0.04 g) or without shelters (0.74 ± 0.04 g) than unfed ones (0.48 ± 0.04 g). A third experiment was conducted to verify these results. Crabs with trimmed or intact chelipeds were either fed or unfed. No shelters were provided. Crabs with trimmed chelipeds (88.57 ± 0%) had higher survival than intact crabs (59.76 ± 7.56%) regardless of whether they were fed or starved; and fed crabs (0.82 ± 0.04 g) had higher mean body weight than unfed crabs (0.61 ± 0.07 g) regardless of whether chelipeds were intact or trimmed. These results indicate that trimming or total removal of chelipeds are effective strategies in reducing cannibalism.

Comparison of antibacterial effect of seven 1-monoglycerides on food-borne pathogens or spoilage bacteria

The aim of this study was to compare under the same conditionsin vitrothe inhibitory effects of seven 1-monoglycerides (MAG) containing fatty acids with a medium chain on ten strains of food-borne pathogens or spoilage gram-positive and gram-negative bacteria (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Micrococcus luteus, Staphylococcus aureus, Citrobacter freundii, Escherichia coli, Proteus mirabilis, Salmonella entericaser.Enteritidis andPseudomonas aeruginosa) and on their growth indicatos. The inhibitory effect of MAGs (monocaprylin, monocaprin, monolaurin, monomyristin, monopalmitin, MAG of undecanoic and 10-undecenoic acids) at a concentration of 25 – 1500 mg·l-1was observed. Growth of bacteria in the presence of MAG was studied by means of optical density of bacteria for 24 h. The data were modelled through a Gompertz equation and the lag-time, the maximum specific growth rate and the maximal value reached were calculated. MAGs inhibited mainly the growth of gram-positive bacteria, which was shown by the extended lag-time, decrease in specific growth rate and decrease in cell density. Inhibitory effects of tested MAGs could be ranked from point of view of the minimum inhibitory concentration: MAG-C12:0 &gt; MAG-C11:0 &gt; MAG-C10:0 &gt; MAG-C14:0 &gt; MAG-C11:1 &gt; MAG-C8:0 &gt; MAG-C16:0.In vitro, no significant inhibitory effects of 1-monoglycerides, with the exception of the highest concentrations applied, on the growth of gram-negative bacteria were detected. The main contribution of this study is to compare the effects of several MAG containing fatty acids with a medium chain under the same conditions on the growth indicators of bacteria.

Effect of feed composition and temperature on food consumption, growth and gastric evacuation of juvenile Atlantic cod ( Gadus morhua L.) and haddock ( Melanogrammus aeglefinus L.)

During sea-cage rearing, Atlantic cod and haddock are fed commercial diets that have high protein content (∼ 50–58%) and are designed for optimum growth at temperatures of 10–12 °C. However, these fish spend several months at temperatures below 5 °C in Atlantic Canada, and there are data to suggest that growth could be enhanced at low water temperatures by feeding a diet with lower protein (LP) content and higher lipid. Thus, we explored how dietary protein and lipid (P/L) levels of 42/16 (low protein, LP diet) and 55/11 (high protein, HP diet) and water temperature (11, 6 and 2 °C) influenced the specific growth rate (SGR), hepatosomatic index (HSI), adjusted specific growth rate (SRG A), food consumption (FC), gross conversion efficiency (GCE) and gastric evacuation (GE) of juvenile Atlantic cod and haddock. Several temperature and species-specific effects were observed for the measured variables. Significant decreases in SGR, SGR A and FC (range 60–96%) were evident for both species when reared at 2 vs. 11 °C. The GCE of haddock was 46 and 31% (for HP and LP diets, respectively) higher than that measured for Atlantic cod at 11 °C, but 35 and 40% lower at 2 °C. With regards to the effects of dietary protein level, it was found that while feed composition did not affect growth rate (with the exception of haddock at 11 °C) or GE, GCE was significantly lower in fish fed the LP diet. These results indicate that 1) low temperatures present a particular challenge to haddock aquaculture; and 2) based on the similar growth rate, but lower GCE values, there is no advantage to feeding an LP diet even at cold temperatures.

Flat panel airlift photobioreactors for cultivation of vegetative cells of microalga Haematococcus pluvialis

The novel flat panel airlift photobioreactor (FP-ALPBR) was proposed as an alternative system for the cultivation of Haematococcus pluvialis NIES-144. Changes in the efficiency of the system were tested in response to variations in two engineering parameters: the ratio between the downcomer and riser cross-sectional areas ( A d / A r ) and the size of the system (as determined by the length of the panel) and to one operating parameter: the superficial gas velocity ( u sg ). The best growth performance was obtained by operating the system at a superficial velocity of 0.4 cm s −1 and with a downcomer-to-riser cross-sectional area ratio of 0.4. The 17-l FP-ALPBR system was capable of giving reasonable growth characteristics with a maximum cell density of 4.1 × 10 5 cell ml −1 and specific growth rate of 0.52 day −1 being achieved. A similar level of performance was obtained from the 90-l FP-ALPBR system, i.e., cell density = 40 × 10 4 cell ml −1 but with a slight decrease in specific growth rate to 0.39 day −1. The performances of these two differently sized FP-ALPBRs were compared with two conventional cylindrical airlift photobioreactors (C-ALPBRs) of different dimensions. The 90-l FP-ALPBR exhibited reasonably good performance when compared with the two 17-l systems (both C- and FP-ALPBRs); however, the best growth rate was observed using the 3-l C-ALPBR. Semi-continuous cultures, which could be periodically harvested at a reasonably high growth rate, were successfully created. Of all the systems investigated in this study, the 90-l FP-ALPBR was found to be the most cost-effective, as it could cultivate 18 g of alga for approximately US$ 21.

The effect of low-intensity coherent extremely high frequency electromagnetic radiation on growth parameters for Enterococcus hirae bacteria

It is found that for Enterococcus hirae ATCC9790 bacteria grown in anaerobic conditions, one-hour exposure to low-intensity (radiant power of 0.06 mW/cm2) coherent extremely high frequency electromagnetic radiation (from 45 to 53 GHz), or millimeter electromagnetic radiation, leads to an appreciable increase in latent growth time and to a decrease in specific growth rate; herein, the effects intensify as the frequency increases from 49 to 53 GHz. The result is enhanced at an increase in the radiation duration from 30 min to 1 h; however, a further increase in the exposure time up to 2 h does not lead to intensification of the effect. It is shown that the effect of extremely high frequency electromagnetic radiation on Enterococcus hirae does not depend on pH of the medium (pH 6.0 or 8.0). It may be expected that these bacteria have protective or reparation mechanisms that compensate long-term action of this radiation; it is not improbable that various mechanisms of pH regulation are present as well.

Effects of post-induction feed strategies on secretory production of recombinant streptokinase in Escherichia coli

The effects of post-induction nutrient feed rates, on recombinant streptokinase production in fed-batch processes, were investigated using various feed profiles. Recombinant streptokinase was produced using a secretory expression system and was induced by a temperature up-shift, using a temperature-sensitive λ PL promoter. The specific growth rates decreased sharply upon induction of recombinant protein expression, thus necessitating a variable feed strategy in the post-induction phase. The various feed profiles employed in the post-induction phase included constant feed rates, linearly increasing feed rate and exponentially varying feed rates. Significant differences were obtained in the specific activity of streptokinase produced in these fed-batch processes. A maximum activity per unit biomass of 4.96 × 10 6 and 4.43 × 10 6 IU/g DCW was achieved for exponentially decreasing feed and linearly increasing feed, respectively. The decrease in specific growth rate during the post-induction phase was also less pronounced in these cases in comparison to other fed-batch experiments. It was observed that streptokinase productivity is governed by the nutrient feed rate per unit biomass at a critical juncture after induction. The highest activity per unit biomass was obtained when the nutrient feed rate per unit biomass was around 0.7–0.8 g glucose (g DCW) −1 h −1, between 2 and 4 h after induction.

Effects of increased suspended sediment on growth rate and gill condition of two southern Appalachian minnows

Despite the recognition that increased suspended sediment concentration (SSC) is a correlate of imperilment for native riverine fishes, research is limited on the effects of SSC on small non-game species. This study quantifies the impact of suspended sediment on fish growth and gill condition of two stream-dwelling minnows. Specific growth rate (i.e., percent change in mass per day) and gill condition (i.e., lamellar thickness and interlamellar area) were measured in young-of-year whitetail shiners, Cyprinella galactura, and federally threatened spotfin chubs, Erimonax monachus, exposed for 21 days to increased SSC (0, 25, 50, 100, and 500 mg L−1). Exposure to elevated SSC caused a significant decrease in specific growth rate in both species and at all life stages tested. The effect of increased SSC was greatest in spotfin chubs, which exhibited a 15-fold decrease in specific growth rate at the highest treatment (500 mg L−1). Effects of increased SSC were least for 8–9-month-old whitetail shiners, which had growth rates similar to controls for 25, 50, and 100 mg L−1 treatments. These minnows exhibited a greater response to increasing SSC than salmonids at low to moderate SSC, and a lesser response at higher sediment levels. Gill damage was minimal at the three lowest treatment levels, moderate at 100 mg L−1 and severe at 500 mg L−1, indicating that respiratory surfaces of upland minnows may be much more sensitive than other species. Specific growth rate decreased significantly with increasing gill lamellar thickness, suggesting that respiratory impairment is one mechanism responsible for negative impacts of excessive sediment on small riverine fishes.

Responses of the photosynthetic machinery of Spirulina maxima to induced reactive oxygen species

The photosynthetic machinery of Spirulina maxima was studied when subjected to induced reactive oxygen species (ROS) to examine the organism's responses to stress. Significant decreases in both photosynthetic efficiency and growth rate were observed. Exposure to 0.01 mmol H(2)O(2)/(g cell), which induced the lowest specific intracellular ROS level (siROS) led to a 15% decrease in specific growth rate; an increase in siROS by 70-fold led to a 25% decrease in specific growth rate. Similarly, siROS induced by 0.01 mmol H(2)O(2)/(g cell) led to 15% inhibition in photosynthetic efficiency, while an increase in siROS by 40- or 70-fold led to about 60% inhibition in photosynthetic efficiency. To further understand the effects of induced ROS on photosynthetic machinery, we performed a detailed pigmentation analysis as well as analyzed Phycobilisomes (PBS), Photosystem II (PSII), and Photosystem I (PSI), the three important components of cyanobacterial photosynthetic apparatus. We found carotenoids (beta-carotene and lutein) to be most sensitive to siROS. Also, specific levels of phycocyanin and allophycocyanin, which are important PBS pigments, decreased significantly in response to H(2)O(2). Further, electron transport assays revealed that ROS cause damage primarily to PSII, whereas they do not significantly affect PSI in comparison; siROS induced by 0.01 mmol H(2)O(2)/(g cell) led to a 15% inhibition of PSII, and increase in siROS by 9-, 40-, and 70-fold led to 22%, 36%, and 46% inhibition, respectively.

Bcl-2 over-expression reduced the serum dependency and improved the nutrient metabolism in a NS0 cells culture

The over-expression of Bcl-2 has greatly improved the culture period, specific growth rate, and maximum viable cell density of NS0 cells culture under low serum condition. Further analysis of these data suggests that a saturation model of the Monod type can be used to represent the relationships of specific growth rate and initial serum concentration. The μmax andKs for the Bcl-2 cell line is 0.927 day−1 and 0.947% (v/v) respectively, which are 21% greater and 7% lower respectively than its control counterpart. Study on the amino acid supplementation revealed that Bcl-2 cell lines possess greater improvement in the specific growth rate and maximum viable cell density compared to the control cell lines. A further increase in the amino acid supplementation has resulted a 17% decrease in specific growth rate and no improvement in maximum viable cell density in the control culture. However, the Bcl-2 cell line exhibited a better growth characteristic in this culture condition compared to that of control cell lines. The higher specific growth rate and maximum viable cell density of the Bcl-2 cell line in medium fortified with serum and MEM EAA suggested a more efficient nutrient metabolism compared to that in the control cell line. The low serum and amino acid utilisation rate and the higher cell yield may prove to be important in the development of serum/protein free culture.

Growth kinetics of EDTA biodegradation by Burkholderia cepacia

A pure culture of an EDTA-degrading strain was isolated from the Taiwan environment. It was identified as Burkholderia cepacia, an aerobic bacterium, elliptically shaped with a length of 5–15 μm. The degradation assay showed that the degradation efficiency of Fe-EDTA by B. cepacia was approximately 91%. Evaluation of kinetic parameters showed that Fe-EDTA degradation followed substrate inhibition kinetics. This is evident from the decrease in specific growth rate with an increase in the initial substrate concentration greater than 500 mg/l. To estimate the kinetic parameters – μmax, K S and K I , five substrate–inhibition models were used. From the results of non-linear regression, the value of μmax ranged from 0.150 to 0.206 d−1, K S from 74 to 87 mg/l, and K I from 890 to 2289 mg/l. The five models were found to underestimate the maximum specific growth rate by 1.5–3.7. Therefore, predictions based on these models would result in lower predicted value than those from the experimental kinetic data.

The effect of temperature and pH on the growth of lactic acid bacteria: a pH-auxostat study

The growth of Streptococcus salivarius subsp. thermophilus, Lactococcus lactis subsp. lactis, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus and Lactobacillus paracasei was studied in a pH-auxostat. The computer-controlled smooth change of pH or temperature was used to study the effect of pH and temperature on the culture characteristics (specific growth rate μ, growth yield Y ATP and specific lactate production rate Q ATP). The behaviour of μ and Q ATP with an increase of temperature suggested that ATP production capacity was an important factor in determining the maximum growth rate of lactic acid bacteria (LAB). The decrease of Y ATP with increase of temperature resulted in the decrease of specific growth rate while Q ATP remained constant or even increased. With the decrease of pH, decrease of both Y ATP and Q ATP was observed. S. thermophilus St20 having the highest maximum specific growth rate of 2.2 h −1 at 44 °C was the most acid sensitive strain. The L. paracasei E1H3 having the lowest μ max was the most tolerant strain to pH change. The behaviour of mixed culture of L. bulgaricus and S. thermophilus in milk in a pH-auxostat with pH-decrease was in agreement with the pure culture experiments of the same species. The study showed that pH-auxostat with smooth controlled change of pH and temperature is an effective method for determination of technological characteristics and comparative physiological study of LAB.

Kinetics of chlorophenol degradation by benzoate-induced culture of Rhodococcus erythropolis M1

A pure culture of Rhodococcus erythropolis was isolated with the ability to degrade 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol. Degradation of 2-chlorophenol by the uninduced culture of Rhodococcus erythropolis began after a prolonged lag period and complete mineralization of the substrates took 45 days. With the aim of reducing the lag period and subsequently improving the rate of degradation, the cells of the isolate were induced with benzoate, phenol, toluene and catechol individually. Benzoate-induced cells showed the highest rate of degradation and were thus used for the study of the degradation kinetics of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol. Complete mineralization of these substrates was achieved up to a concentration of 300, 100 and 50 mg l−1 respectively. Degradation of the chlorophenols was initiated without any significant lag and took the remarkably short time periods of 84, 64 and 144 h for the highest concentrations of the substrate. Evaluation of kinetic parameters showed chlorophenol degradation to follow substrate inhibition kinetics. This is evident from the decrease in specific growth rate, growth yield and substrate uptake rate with increase in the initial substrate concentrations. Toxicity of the chlorophenols was observed to depend on the position of chlorine on the benzene ring and the degree of chlorination.