Biomedical subjects

N Kalogerakis

Publications and source records attributed to N Kalogerakis.

8 recordsLinked to original sources

PubMed2005

Bacterial community dynamics during in-situ bioremediation of petroleum waste sludge in landfarming sites.

In-situ bioremediation of petroleum waste sludge in landfarming sites of Motor Oil Hellas (petroleum refinery) was studied by monitoring the changes of the petroleum composition of the waste sludge, as well as the changes in the structure of the microbial community, for a time period of 14 months. The analyses indicated an enhanced degradation of the petroleum hydrocarbons in the landfarming areas. A depletion of n-alkanes of approximately 75-100% was obtained. Marked changes of the microbial communities of the landfarms occurred concomitantly with the degradation of the petroleum hydrocarbons. The results obtained from terminal restriction fragment length polymorphism (T-RFLP) analysis of polymerase chain reaction (PCR) amplified 16S rRNA genes demonstrated that bacteria originating from the refinery waste sludge and newly selected bacteria dominated the soil bacterial community during the period of the highest degradation activity. However, the diversity of the microbial community was decreased with increased degradation of the petroleum hydrocarbons contained in the landfarms. T-RFLP fingerprints of bacteria of the genera Enterobacter and Ochrobactrum were detected in the landfarmed soil over the entire treatment period of 14 months. In contrast, the genus Alcaligenes appeared in significant numbers only within the 10 month old landfarmed soil. Genes encoding catechol 2,3-dioxygenase (subfamily I.2.A) were detected only in DNA of the untreated refinery waste sludge. However, none of the genes known to encode the enzymes alkane hydroxylase AlkB, catechol 2,3-dioxygenase (subfamily I.2.A) and naphthalene dioxygenase nahAc could be detected in DNA of the landfarmed soils.

Biodegradation, Environmental↗

PubMed2001

Solid-phase microextraction versus single-drop microextraction for the analysis of nitroaromatic explosives in water samples.

This paper compares solid-phase microextraction (SPME) with a recently developed extraction method called single-drop microextraction (SDME) for the analysis of nitroaromatic explosives in water samples. The two techniques are examined in terms of procedure, chromatographic analysis and method performance. All practical considerations for both techniques are also reviewed. SPME requires dedicated apparatus and is relatively expensive, as the fiber's lifetime is limited. However, it has the advantages over SDME that it can be easily used for headspace analysis and has lower detection limits for all the target analytes. SDME requires more elaborate manual operations, thus affecting linearity and precision.

Gas Chromatography-Mass Spectrometry↗

PubMed2001

Application of solvent microextraction to the analysis of nitroaromatic explosives in water samples.

The application of solvent microextraction to the analysis of nitroaromatic explosives is presented. Extraction of 11 nitroaromatics was achieved by suspending 1 microl of organic solvent to the tip of a microsyringe in a stirred aqueous solution. Parameters such as extraction solvent, stirring rate, salt concentration and sampling time were studied and optimized. The limits of detection using bench-top quadrupole mass spectrometry and short extraction times (15 min) were found to be between 0.08 and 1.3 microg/l and the relative standard deviations ranged between 4.3 and 9.8%. Although precision and accuracy of quantification of the method are still needed, solvent microextraction proved to be a fast, simple and inexpensive tool for preconcentration and matrix isolation of nitroaromatics on a microscale.

Evaluation Studies as Topic↗

PubMed1994

Cell cycle dynamics of microcarrier cultures.

In anchorage-dependent cell microcarrier cultures knowledge of the cell's growth kinetics is necessary in order to design and successfully operate bioreactors, particularly on a large scale. However, in addition to growth kinetics, an understanding of the physiological state of the culture is also important. In this paper the cell cycle progression of Vero and MRC-5 microcarrier cultures have been observed utilizing a flow cytometer. Flow cytometry analysis enabled the differentiation of the various phases of the cell cycle as the culture moved from initial inoculation to the stationary, or confluent stage. Not only was the flow cytometer able to distinguish contact inhibited cells from noncontact inhibited cells, but the measured fraction of contact inhibition cells were found to be in agreement with fractions predicted from a previously developed cellular automation model for microcarrier cultures. Further, the data from the stationary phase was used to quantify the death rate in microcarrier cultures.

Animals↗

PubMed1994

Optimization of the physiochemical parameters for the culture of Bombyx mori insect cells used in recombinant protein production.

Silkworm (Bombyx mori, Bm5) cell growth at different environmental conditions was systematically studied in controlled bioreactors. The physiochemical parameters, which affect the growth of Bm5 cells, were defined and optimized. The growth rate was maximal at a medium osmolality of about 370 mosm kg-1; and more than 90% of the maximum growth rate was achieved with osmolality between 350 and 385 mosm kg-1. The optimum pH for Bm5 cell growth was from 6.10 to 6.30. Moreover, the effect of dissolved oxygen concentrations (higher than 20% air saturation) on growth was minimal. However, the maximum cell density decreased markedly with dissolved oxygen tensions less than 20%. The shear protection additive Pluronic F-68 had a very important effect on the growth of Bm5 cells in bioreactors with an optimum concentration of 0.2% (w/v). Compared to the original culture condition, the optimized conditions resulted in a twofold increase in cell yield and a reduced population doubling time from 48 to 36 h. Furthermore, the yield of a recombinant protein (CAT) was increased substantially in the optimized cultures.

Animals↗

PubMed1994

Effect of endogenous proteins on growth and antibody productivity in hybridoma batch cultures.

It has been shown that some B-cell hybridomas secrete autocrine factors in vitro which can influence cell metabolic processes. Rather than screen specifically for suspected cytokines, that may or may not affect our cell line, we have examined the lumped effects of intracellular and secreted factors on cell proliferation and monoclonal productivity in hybridoma batch cultures. Firstly, supplements of total soluble intracellular proteins combined with other intracellular metabolites were found to both decrease the specific growth rate and increase the antibody production rate at higher concentrations in batch culture. This is an important consideration in high cell density cultures, such as perfusion systems, where a reduction of growth by the presence of intracellular factors may be compensated by an increase in MAb production. In addition, flow cytometry data revealed that the average cell cycle G1 phase fraction was unaffected by the variation in the maximum specific growth rates during the exponential growth phase, caused by the addition of intracellular factors; this suggests that higher MAb productivity at lower growth rates are not a result of cell arrest in the G1 phase. Secondly, secreted extracellular proteins larger than 10,000 Daltons, which were concentrated from spent culture supernatant, were shown to have no significant effect on growth and specific MAb productivity when supplemented to batch culture at levels twice that encountered late in normal batch culture. This indicates that endogenous secreted cytokines, if at all present, do not play a major autocrine role for this cell line.

Animals↗

PubMed1992

Low-serum medium development for human diploid fibroblast microcarrier cultures.

A new medium supplement mixture, PPRF92, has been developed to enable the serial subculture of human diploid fibroblasts (MRC-5 cells) on microcarriers. Furthermore, the PPRF92 supplements enable cell growth at serum levels as low as 1%. Through an optimization programme, the PPRF92 supplements have evolved into a simple mixture with the concentrations of key components at a level that makes the overall cost very competitive with medium containing 10% foetal bovine serum (FBS). Furthermore, the PPRF92 supplement mixture is most efficacious when FBS is replaced with the cheaper, and more widely available, adult bovine serum (ABS). Although medium exchange with serum is necessary in order to achieve confluence on microcarriers, the PPRF92 mixture is only necessary at the initiation of each passage. Using the medium replenishment protocol that has been developed in our laboratory, MRC-5 cells were successfully serially passaged through 13 bead-to-bead transfers on microcarriers in DMEM/F12 medium enriched with the PPRF92 supplement mixture reported here, and 1% ABS.

Blood↗

PubMedDate not supplied

Optimum infection conditions for recombinant protein production in insect cell (Bm5) suspension culture.

The baculovirus/insect cell expression system is an efficient and practical method for the production of many active therapeutic proteins on a large scale. The advantages of suspension cultures have been demonstrated with the study of a baculovirus/insect cell (BmNPV/Bm5) expression system for the production of recombinant chloramphenicol acetyltransferase (CAT), a model heterologous protein. Key infection parameters such as infection time and multiplicity of infection were examined systematically for the maximization of protein production. Furthermore, emphasis was placed on the development of possible medium replenishment strategies, which were necessary to achieve higher volumetric protein production from the infection of high-density cell cultures without sacrificing specific protein productivity. The highest protein production was achieved with the infection of suspended cells in the mid to late exponential growth phase.

Animals↗