Studies on N-limited growth of diatoms in dialysis culture

N-limited growth of Skeletonema costatum (Grev.) Cleve in dialysis culture has been studied. The division rate of exponentially growing cells was independent of the nitrate concentration in the growth medium in the range from 886 down to 0.25 μM N-salt, while no growth beyond one division took place in cultures to which no nitrogen salt was added. The half saturation constant, K₃, for growth must, therefore, be in the range 0–0.13 μM, provided the growth-nutrient relationship is hyperbolic for S. costatum.Contrary to growth rate, cellular chlorophyll and protein were markedly reduced in media poor in nitrogen salts. A dialysis culture chamber was used to demonstrate that the measurement of half saturation constants for S. costatum was influenced by stirring, the stirred culture growing almost twice as fast as the unstirred control under identical conditions. The ability of diatoms to grow rapidly at low nitrogen levels was used to remove nutrients from sewage enriched media. Removal efficiencies corresponding to 80 and 90 % were obtained for nitrate and ammonia, respectively, using the diatom Phaeodactylum tricornutum Bohlin. It was found that both this diatom and S. costatum as well as Thalassiosira pseudonana Hust (Hasle) tolerated ammonia up to at least 450 μM with no deleterious effects on growth rate.     

Removal of amantadine hydrochloride by dialysis in patients with renal insufficiency.

Two patients with Parkinson''s disease and renal insufficiency had excessively high concentrations of amantadine hydrochloride in the blood. The amounts of the drug removed by hemodialysis and peritoneal dialysis were small. However, since extrarenal elimination is negligible in such patients, frequently repeated dialysis may be required to remove the drug.     

Inhibition of growth of tubercle bacilli by ali-esterase inhibitors in various culture media

Summary The effect of the potent ali-esterase inhibitor E 600 (paraoxon) on the growth of tubercle bacilli is potentiated by the addition of Tween 80 to the medium. This may be due to a change in the permeability of the bacteria for the inhibitor. Growth of tubercle bacilli from sputa is also inhibited by E 600 in the haemolysed human blood medium of Price. Cultures of tubercle bacilli in media with E 600 begin to grow after some time, when the inhibitor has broken down. The results obtained by the method of Price indicate that growth of the cultures does not originate from a few resistant cells but from the whole population which may have regained the ali-esterase activity essential to their growth.     

Model for bacterial culture growth rate throughout the entire biokinetic temperature range.

The "square-root" relationship proposed by Ratkowsky et al. (J. Bacteriol. 149:1-5, 1982) for modeling the growth rate of bacteria below the optimum growth temperature was extended to cover the full biokinetic temperature range. Two of the four parameters of this new nonlinear regression model represent minimum and maximum temperature bounds, respectively, for the predicted growth of the culture. The new model is easy to fit and has other desirable statistical properties. For example, the least-squares estimators of the parameters of the model were almost unbiased and normally distributed. The model applied without exception to all bacterial cultures for which we were able to obtain data. Results for 30 strains are reported.     

Continuous observations of bacterial gliding motility in a dialysis microchamber: The effects of inhibitors

Use of a dialysis microchamber has allowed continuous observations on the same set of gliding bacteria during changes in the composition of the perfused medium. This procedure has revealed the presence of an adaptive, cyanide-insensitive metabolic pathway, which allows cyanide-treated Flexibacter BH3 to begin gliding again at a reduced rate when glucose is the substrate. In addition, it has revealed that individual flexibacter cells can maintain their gliding motility for up to 20 h in the absence of exogenous substrate.Gliding in Flexibacter BH3 was prevented by those inhibitors blocking the electron transport process. Inhibitors of glucose metabolism did not prevent motility, since the flexibacters obviously metabolize endogenous substrate under such circumstances. Proton ionophores, which induce membrane depolarization, rapidly inhibited gliding in Flexibacter BH3. This inhibition was irreversible in the case of gramicidin S. Gliding was not inhibited by cytochalasin B or antiactin antibody. High concentrations of Ca²⁺ were particularly inhibitory to the gliding process. The significance of these results is discussed in relation to a possible mechanism of gliding involving the generation of rhythmical contractions in the outer cell membrane of Flexibacter BH3.Abbreviations used CCCP carbonyl cyanide m-chlorophenyl hydrazone - DNP p-dinitrophenol - GMCS gramicidin S - HQNO 2-heptyl-4-hydroxyquinoline N-oxide - PCMB p-chloromercuribenzoate - CM complete Lewin's medium - BS Lewin's basal salts     

Model for the feedback control system of bacterial growth. II. Growth in continuous culture

A mathematical model is developed that describes substrate limited bacterial growth in a continuous culture and that is based upon the conceptual framework elaborated in a previous paper for describing the feedback control system of cell growth [S. Bleecken, (1988). J. theor. Biol. 133, 37.] Central to the theory are the ideas that the limiting substrate is converted into low molecular weight building blocks of macromolecular synthesis which again are converted into biomass (RNA and protein) and that the rates of RNA and protein synthesis are controlled by the intracellular concentration of building blocks. It is shown that a continuous culture can be simulated by two interconnected feedback control systems the actuating signals of which are limiting substrate concentration and the intracellular concentration of building blocks, respectively. Three types of steady-states are found to appear in a continuous culture, besides the well-known stable steady-state of the whole culture there exist two batchlike steady-states of the biotic part of the culture which are metastable. The model is used to analyse the steady-states and their stability properties as well as the dynamic responses of biomass, RNA, protein, building block and substrate concentrations to changes in environmental conditions. Especially the inoculation of a continuous culture and the effects of step changes in dilution rate, inlet substrate concentration and growth temperature are studied in detail. Relations between the growth behaviour of a single cell and that of a continuous culture are derived. The RNA to protein ratio is introduced as a rough measure of the physiological state of cells and it is shown that a cell reacts to environmental changes with a simple pattern of basic responses in growth rate and physiological state. There are reasons to assume that the model presented is the minimal version of a structured model of bacterial growth and represents an optimum compromise between biological relevance and mathematical practicability.     

The inhibition of bacterial growth by ochratoxin A.

A series of bacterial species was examined for their sensitivity to ochratoxin A. Only grampositive bacteria could be inhibited, generally at a pH lower than 7.0. Bacillus subtilis did not show any reduction of growth rates in presence of ochratoxin A, but had a prolonged lag phase. With Staphylococcus pyogenes var. aureus and Streptococcus faecalis, a prolonged lag phase and a reduction of the growth rate was observed. Most sensitive was Streptococcus faecalis in the exponential-growth phase. The inhibition could be diminished by changing the pH to neutral, or by addition of yeast extract, tetrahydrofolate, or MgSO4. With MgSO4 a complete abolition of the inhibitory effect was achieved, but not with CaCl2. During growth inhibition, protein and RNA synthesis were reduced simultaneously, but not DNA synthesis. Even with the very high concentration of 1 mg/ml, no lethal effect was observed.     

Biodegradation of methyl tert-butyl ether by a pure bacterial culture.

Biodegradation of methyl tert-butyl ether (MTBE) by the hydrogen-oxidizing bacterium Hydrogenophaga flava ENV735 was evaluated. ENV735 grew slowly on MTBE or tert-butyl alcohol (TBA) as sole sources of carbon and energy, but growth on these substrates was greatly enhanced by the addition of a small amount of yeast extract. The addition of H(2) did not enhance or diminish MTBE degradation by the strain, and MTBE was only poorly degraded or not degraded by type strains of Hydrogenophaga or hydrogen-oxidizing enrichment cultures, respectively. MTBE degradation activity was constitutively expressed in ENV735 and was not greatly affected by formaldehyde, carbon monoxide, allyl thiourea, or acetylene. MTBE degradation was inhibited by 1-amino benzotriazole and butadiene monoepoxide. TBA degradation was inducible by TBA and was inhibited by formaldehyde at concentrations of >0.24 mM and by acetylene but not by the other inhibitors tested. These results demonstrate that separate, independently regulated genes encode MTBE and TBA metabolism in ENV735.     

Biodegradation of methyl tert-butyl ether by a bacterial pure culture.

A bacterial strain, PM1, which is able to utilize methyl tert-butyl ether (MTBE) as its sole carbon and energy source, was isolated from a mixed microbial consortium in a compost biofilter capable of degrading MTBE. Initial linear rates of MTBE degradation by 2 x 10(6) cells ml(-1) were 0.07, 1.17, and 3.56 microg ml(-1) h(-1) for initial concentrations of 5, 50, and 500 microg MTBE ml(-1), respectively. When incubated with 20 microg of uniformly labeled [(14)C]MTBE ml(-1), strain PM1 converted 46% to (14)CO(2) and 19% to (14)C-labeled cells within 120 h. This yield is consistent with the measurement of protein accumulation at different MTBE concentrations from which was estimated a biomass yield of 0.18 mg of cells mg MTBE(-1). Strain PM1 was inoculated into sediment core material collected from a contaminated groundwater plume at Port Hueneme, California, in which there was no evidence of MTBE degradation. Strain PM1 readily degraded 20 microg of MTBE ml(-1) added to the core material. The rate of MTBE removal increased with additional inputs of 20 microg of MTBE ml(-1). These results suggest that PM1 has potential for use in the remediation of MTBE-contaminated environments.     

Study of the oxygen effect during growth of a bacterial culture

In study of the oxygen effect in relation to the growth curve ofEscherichia coli B, its size was found to be correlated to the stage of growth at which the bacteria were irradiated. The lowest dose reduction factor value (DRF = 1.5) was found with bacteria irradiated at the outset of the logarithmic phase and the highest value (DRF = 2.7) with bacteria in the stationary phase. This phenomenon was observed both in a culture cultivated under aerobic conditions prior to irradiation and in a culture cultivated under anaerobic conditions. The cultivation conditions influenced only the radiosensitivity of the bacteria.     

Removal of ampholines by hollow fiber dialysis: Application to dextransucrase

Ampholines must be removed from proteins that have been purified using isoelectric focusing chromatography before hydrolysis since ninhydrin positive fragments result. Hollow fiber dialysis was shown to be a fast and efficient method for the removal of ampholines from dextransucrase after isoelectric focusing. The purified protein was then subjected to amino acid analysis.