Average Dilution Rate Research Articles

Testing the yield of a pilot‐scale bubble column photobioreactor for cultivation of the microalgaRhodomonas salinaas feed for intensive calanoid copepod cultures

A dual column photobioreactor (PBR) (2 × 47 L) with mixed CO₂/air bubbling was tested for cultivation of the microalga Rhodomonas salina as food for live feed copepods. In the continuous growth phase, the cell density was relatively stable at 2.40 ± 0.13 × 10⁶ cells/ml at an average dilution rate of 0.46 ± 0.02 per day throughout the 30‐day experiment. The produced algae had a high content of both total fatty acids (TFA) and free amino acids (FAA). Especially, the harvested algae contained a high proportion of poly‐unsaturated fatty acids that made up 80% of the TFA and of essential amino acids (35% of all FAA), implicating desirable components as feed for copepods. The current PBR was sufficient to feed a culture of the calanoid copepod Acartia tonsa at a density of 2,500 adult/L in ca. 500 L culture with a daily yield of approximately 17 × 10⁶ eggs. To be able to sustain the integrated copepods production, the suggested volume of the algae cultures should be ca. 20% of the copepod culture volume.

FROZEN SEMEN PRODUCTION PERFORMANCE OF KARAN FRIES BULLS

A study was conducted to assess semen output characteristics of 4648 ejaculates of 52 Karan Fries bulls (Holstein Friesian crossbreds with 50 to 75% exotic inheritance) maintained at Artificial Breeding Research Centre, NDRI, Karnal, India. The objective of this study was to estimate expected frozen semen dose production. Semen production data were analysed using standard statistical tools. Age of the Karan Fries bulls (KF) at the time of collection ranged from 1.90 to 8.13 years, with a mean of 3.32 ± 0.18 years. The average ejaculate volume (VOL, ml), mass activity (MA), initial motility (IM, %), sperm concentration per ml (SPC, millions) and total sperm output per ejaculate (SPCE, millions) from 52 KF bulls were 4.68 ± 0.14 (2.74 - 6.98); 2.84±0.02 (2.57 - 3.08); 65.55 ± 0.01 (61.40 - 69.65); 965.71 ± 7.61 (865 - 1067.72) and 4516.90 ± 128.34 (2600 - 6603.41, respectively). The average dilution rate for preservation was found to be 1: 12.07 ± 0.10 with a range of 1:10.81 to 13.35. The expected number of ejaculates that could be frozen per year per bull was 44.46 (21 - 90) and correspondingly expected frozen dose produced per year per bull could be 10048.39 (3500 - 24669) in Karan Fries bulls.

Isolation and characterization of an amino sugar-rich glycopeptide from the surface layer glycoprotein of Thermoanaerobacterium thermosaccharolyticum E207-71

The characterization of surface layers (S-layers) [l] of different clostridia has indicated the presence of covalently linked carbohydrate residues [2,3]. The glycan content comprises up to 20% of the S-layer material and is considerably higher than that of aerobic bacilli [4,5]. There exist great variations, not only in the glycan structures of S-layers of different species of clostridia, but also in the glycans of different strains of the same species [3]. Thermoanaerobacterium thermosaccharolyticum (formerly Clostridium thermosaccharolyticum [6]) strain E207-71 is an anaerobic, thermophilic eubacterium that was isolated from extraction juices of an Austrian beet sugar factory [7]. The bacteria were completely covered by a squarely arranged S-layer lattice consisting of glycoprotein molecules with a centre-to-centre spacing of approximately 12.3 nm when they were continuously grown in the fermenter with an average dilution rate of D = 0.10 hh’ [S]. Each morphological unit consisted of four identical subunits. SDS-polyacrylamide gel-electrophoresis (SDS-PAGE) of the purified S-layer glycoprotein showed distinct

Effects of phenol feeding pattern on microbial community structure and cometabolism of trichloroethylene

Cometabolism of trichloroethylene (TCE) by phenol-fed enrichments was evaluated in four reactors with distinct phenol feeding patterns. The reactors were inoculated from the same source, operated at the same average dilution rate, and received the same mass of phenol over time. Only the timing of phenol addition differed. Reactor C received phenol continuously; reactor SC5 received phenol semicontinuously--alternating between 5 h of feed and 3 h without feed; reactor SC2 alternated between 2 h of feed and 6 h without feed; and reactor P received a single pulse every 24 h. The structure of the enrichments and their capacity for TCE transformation were analyzed. In long-term operation, reactors C and SC5 were dominated by fungi, had higher levels of predators, were more susceptible to biomass fluctuations, and exhibited reduced capacity for TCE transformation. Reactors P and SC2 were characterized by lower levels of fungi, higher bacterial biomass, higher concentrations of TCE-degrading organisms, and higher rates of TCE transformation. After 200 days of operation, rates of TCE transformation increased 10-fold in reactor P, resulting in TCE transformation rates that were 20 to 100 times higher than the rates of the other reactor communities. The cause of this shift is unknown. Isolates capable of the highest rates of TCE transformation were obtained from reactor P. We conclude that cometabolic activity depends upon microbial community structure and that the community structure can be manipulated by altering the growth substrate feeding pattern.

A dense cell culture system for microorganisms using a stirred ceramic membrane reactor incorporating asymmetric porous ceramic filters

A stirred ceramic membrane reactor (SCMR) incorporating asymmetric porous ceramic tubes was found to be effective for maintaining high filtrate flux over a long period of filtering culture. Alumina ceramic filters with mean pore diameters of 0.5 μm at the surface and 25 μm in the inner rough phase were fitted inside a jarfermentor. Filtering performance was enhanced by stirring the culture broth at a higher rate. Membrane fouling was also prevented by stirring. Using this bioreactor system, a dense cell culture of Lactococcus lactis, which is damaged by metabolites produced in the culture supernatant, was attempted by the filtering culture method with the aid of an automatic feeding and filtering system. Preliminary tests on the medium composition in batch cultures showed that the cell growth was severely impaired by excessive consumption of substrates such as glucose, Polypepton, and yeast extract. Even in a fed-filtering culture, the cell concentration was as low as 38 g/l with 56% viability after a 220-h cultivation period with the feeding of a substrate solution containing 12 g/l glucose and 4 g/l yeast extract powder. A high cell concentration of 141 g/l with 94% viability after 238-h cultivation was achieved by fed-filtering massive amounts of a diluted substrate solution containing 6 g/l glucose and 2 g/l yeast extract. Both the yield and productivity of cells were also increased by controlling the feeding of the diluted fresh medium and filtering the supernatant of the dense cell culture. The filtrate volume reached sixty-four times that of the original working volume in the fermentor. The average dilution rate was 0.3 h−1 through the filtering culture. These results showed that the long-lasting and high permeability capacity of the SCMR system fitted with an asymmetric membrane enabled facilitated increases in the concentration and productivity of the cells by continuously removing inhibitory by-products at a high dilution rate.

Heat flux measurements for the fast monitoring of dynamic responses to glucose additions by yeasts that were subjected to different feeding regimes in continuous culture.

Heat measurements have been successfully as an analytical tool for the study of the dynamics of energy metabolism of Saccharomyces cerevisiae and Candida utilis grown in continuous culture under fluctuating substrate supply. A low average dilution rate (D = 0.05 h-1) was maintained either by adding the medium as continuously (dropwise) as possible or (blockwise) by adding the medium at high speed during a short period (D = 0.5 h-1 for 40 s) and not at all during the following period (D = 0.00 h-1 for 360 s). The resulting biological activity was monitored on-line with conventional (O2 and CO2) off-gas analyses, DOT measurements, and heat flux measurements. In C. utilis cultures, the biomass-specific maximum oxygen consumption rate (qO2,max), the biomass yield (Ys,x), and the dynamic responses to a glucose pulse and to a change in feeding regime were not significantly affected by different preceding feeding regimes. In contrast, S. cerevisiae grown in continuous culture with blockwise feed showed a 50% increase in qO2,max and a 25% drop in Ys,x compared to the culture grown with dropwise feed. The dynamic response to a glucose pulse (0.6 g L-1) was slower for the continuous (dropwise) than for the blockwise grown S. cerevisiae. With a second testing method for the dynamic response of the yeasts, the feeding regime was changed. The blockwise fed S. cerevisiae proved to be better "trained" to cope with sudden changes in glucose supply and, therefore, was more "shockproof" toward a change in feeding regime. This clearly points to major differences in the intracellular metabolic flux control between the yeasts. These findings are of relevance for industrial baker's yeast production, where reactor mixing times of one to several minutes are not uncommon. The observed, heat production, together with the dissolved oxygen concentration, appeared to give the fastest response to actual changes in the culture. It is suggested that heat measurements can be a very useful tool to monitor and control the growth of S. cerevisiae in laboratory and industrial fermenter operations.

Growth and enrichment of pentachlorophenol-degrading microorganisms in the nutristat, a substrate concentration-controlled continuous culture

The nutristat, a substrate concentration-controlled continuous culture, was used to grow pentachlorophenol (PCP)-degrading microorganisms. The PCP concentration control system consisted of on-line measurement of the PCP concentration in the culture vessel with a tangential filter and a flowthrough spectrophotometer. With PCP concentrations between 45 and 77 microM, a stable situation was established in the nutristat, with an average dilution rate of 0.035 +/- 0.003 h-1. Compared with those of fed-batch cultures and chemostat cultures, the growth rates of microorganisms in the PCP nutristat were significantly higher, leading to considerable time savings in the enrichment procedure. In addition, PCP accumulation to severe inhibitory levels in the culture is prevented because the set point determines the (maximum) PCP concentration in the culture. The use of the nutristat as a tool for the growth of bacteria that degrade toxic compounds is discussed.

Extractive acetonobutylic fermentation by coupling ultrafiltration and distillation

An extractive acetonobutylic fermentation process is developed by integrating bioproduction, Ultrafiltration, and distillation, providing simultaneous retention of biomass, selective removal of inhibitors from the permeate, as well as separation and purification of acetone-butanol-ethanol solvents. Successive batch fermentations were performed with normal pressure distillation (98 degrees C), which permitted prolonging and enhancing (by a factor of 3) solvent production, with very few volume exchanges of medium (average dilution rate ws 0.002 h(-1)), and recovering on-line concentrated solvents. Different operating conditions were also tested in order to study the presence of extracellular autolytic enzymes as inhibition factors: It was shown that, (1) extracellular autolytic activity remains low during the larger part of fermentations, even without enzyme-inactivating thermotreatment in the distillation boiler, and (2) high-temperature distillation causes deleterious effects to the culture medium for long duration treatments. Progressive improvements of the process were achieved, first, by managing continuous runs, providing a minimum renewal of the culture medium and, mainly, by decreasing temperature and pressure of distilation. Solvent productivity then reached 2.6 g/L h for a 0.036 h(-1) average dilution rate, corresponding to a feed concentration of 156 g/L glucose actually consumed.

Phenotypic variability of the sensitivity to cycloserine of Klebsiella aerogenes NCTC 418, growing in chemostat culture.

The susceptibility of Klebsiella aerogenes to cycloserine varied according to the growth conditions. In batch culture, cells were less susceptible to the antibiotic when glycine was present in the medium, presumably due to competition between glycine and cycloserine for the uptake system by which glycine, D-alanine and cycloserine are transported into the cell. In the chemostat at average dilution rates, ammonia-limited cultures were more susceptible to the antibiotic than were glucose-limited cultures. Under phosphate-limiting conditions cultures were at least ten times less susceptible. Under ammonia and phosphate limitation the susceptibility increased with increasing growth rate. The sensitivity of glucose-limited cells was independent of the growth rate. A high-affinity uptake system for cycloserine (as measured by D-alanine transport) was present in ammonia- and glucose-limited cells, but not in phosphate-limited cells. Thus, the phenotypically defined alterations in the susceptibility of the bacterium to cycloserine could be correlated with variations in its uptake system for the antibiotic.