Dialysis culture of microorganisms: design, theory, and results

Dialysis rolled scaffold bioreactor allows extended production of monoclonal antibody with reduced media use

Rapidly expanding biopharmaceutical market demands more cost-effective platforms to produce protein therapeutics. To this end, novel approaches, such as perfusion culture or concentrated fed-batch, have been explored for higher yields and lower manufacturing costs. Although these new approaches produced promising results, but their wide-spread use in the industry is still limited. In this study, a dialysis rolled scaffold bioreactor was presented for long-term production of monoclonal antibodies with reduced media consumption. Media dialysis can selectively remove cellular bio-wastes without losing cells or produced recombinant proteins. The dialysis process was streamlined to significantly improve its efficiency. Then, extended culture of recombinant CHO cells for 41 days was successfully demonstrated with consistent production rate and minimal media consumption. The unique configuration of the developed bioreactor allows efficient dialysis for media management, as well as rapid media exchange to harvest produced recombinant proteins before they degrade. Taken together, it was envisioned that the developed bioreactor will enable cost-effective and long-term large-scale culture of various cells for biopharmaceutical production.

Recent advances in fed-batch microscale bioreactor design

Advanced fed-batch microbioreactors mitigate scale up risks and more closely mimic industrial cultivation practices. Recently, high throughput microscale feeding strategies have been developed which improve the accessibility of microscale fed-batch cultivation irrespective of experimental budget. This review explores such technologies and their role in accelerating bioprocess development. Diffusion- and enzyme-controlled feeding achieve a continuous supply of substrate while being simple and affordable. More complex feed profiles and greater process control require additional hardware. Automated liquid handling robots may be programmed to predefined feed profiles and have the sensitivity to respond to deviations in process parameters. Microfluidic technologies have been shown to facilitate both continuous and precise feeding. Holistic approaches, which integrate automated high-throughput fed-batch cultivation with strategic design of experiments and model-based optimisation, dramatically enhance process understanding whilst minimising experimental burden. The incorporation of real-time data for online optimisation of feed conditions can further refine screening. Although the technologies discussed in this review hold promise for efficient, low-risk bioprocess development, the expense and complexity of automated cultivation platforms limit their widespread application. Future attention should be directed towards the development of open-source software and reducing the exclusivity of hardware.

High-throughput screening for high-efficiency small-molecule biosynthesis

Systems metabolic engineering faces the formidable task of rewiring microbial metabolism to cost-effectively generate high-value molecules from a variety of inexpensive feedstocks for many different applications. Because these cellular systems are still too complex to model accurately, vast collections of engineered organism variants must be systematically created and evaluated through an enormous trial-and-error process in order to identify a manufacturing-ready strain. The high-throughput screening of strains to optimize their scalable manufacturing potential requires execution of many carefully controlled, parallel, miniature fermentations, followed by high-precision analysis of the resulting complex mixtures. This review discusses strategies for the design of high-throughput, small-scale fermentation models to predict improved strain performance at large commercial scale. Established and promising approaches from industrial and academic groups are presented for both cell culture and analysis, with primary focus on microplate- and microfluidics-based screening systems.

Enhancement of solubilization and biodegradation of polyaromatic hydrocarbons by the bioemulsifier alasan

Alasan, a high-molecular-weight bioemulsifier complex of an anionic polysaccharide and proteins that is produced by Acinetobacter radioresistens KA53 (S. Navon-Venezia, Z. Zosim, A. Gottlieb, R. Legmann, S. Carmeli, E. Z. Ron, and E. Rosenberg, Appl. Environ. Microbiol. 61:3240-3244, 1995), enhanced the aqueous solubility and biodegradation rates of polyaromatic hydrocarbons (PAHs). In the presence of 500 microg of alasan ml-1, the apparent aqueous solubilities of phenanthrene, fluoranthene, and pyrene were increased 6.6-, 25.7-, and 19.8-fold, respectively. Physicochemical characterization of the solubilization activity suggested that alasan solubilizes PAHs by a physical interaction, most likely of a hydrophobic nature, and that this interaction is slowly reversible. Moreover, the increase in apparent aqueous solubility of PAHs does not depend on the conformation of alasan and is not affected by the formation of multimolecular aggregates of alasan above its saturation concentration. The presence of alasan more than doubled the rate of [14C]fluoranthene mineralization and significantly increased the rate of [14C]phenanthrene mineralization by Sphingomonas paucimobilis EPA505. The results suggest that alasan-enhanced solubility of hydrophobic compounds has potential applications in bioremediation.

Dialysis culture enables more accurate determination of MIC of benzylpenicillin for Borrelia burgdorferi than does conventional procedure

A constant benzylpenicillin (penicillin G) concentration for determination of the MIC for strains of Borrelia burgdorferi was achieved by dialysis culture. The strains were grown in dialysis membrane bags with daily transfer to tubes with freshly added benzylpenicillin. The MICs decreased by one or several dilution steps compared with the conventional procedure.

Measurement of minimum substrate concentration (Smin) in a recycling fermentor and its prediction from the kinetic parameters of Pseudomonas strain B13 from batch and chemostat cultures

The minimum substrate concentration required for growth, Smin, was measured for Pseudomonas sp. strain B13 with 3-chlorobenzoate (3CB) and acetate in a recycling fermentor. The substrates were provided alone or in a mixture. Smin values predicted with kinetic parameters from resting-cell batches and chemostat cultures differed clearly from the values measured in the recycling fermentor. When 3CB and acetate were fed as single substrates, the measured Smin values were higher than the individual Smin values in the mixture. The Smin in the mixture reflected the relative energy contributions of the two substrates in the fermentor feed. The energy-based maintenance coefficients during zero growth in the recycling fermentor were comparable for all influent compositions (mean +/- standard deviation, 0.34 +/- 0.07 J mg [dry weight]-1 h-1). Maintenance coefficient values for acetate were significantly higher in chemostat experiments than in recycling-fermentor experiments. 3CB maintenance coefficients were comparable in both experimental systems. The parameters for 3CB consumption kinetics varied remarkably with the experimental growth conditions in batch, chemostat, and recycling-fermentor environments. The results demonstrate that the determination of kinetic parameters in the laboratory for prediction of microbial activity in complex natural systems should be done under conditions which best mimic the system under consideration.

Survival ofEscherichia coli andYersinia enterocolitica in stream water: Comparison of field and laboratory exposure

Experiments were done to compare the influence of three aquatic exposure methods on the behavior of pathogenic and nonpathogenic enteric bacteria (Yersinia enterocolitica andEscherichia coli). Bacterial suspensions were exposed to stream water in membrane diffusion chambers in situ as well as in the laboratory using a large vessel of stream water and in enclosed bottles. The persistence of culturability of the bacterial suspensions was dependent upon the method of aquatic exposure. This difference was most apparent during the initial six days of each experiment. A steady decline in colony forming units was seen after a short stationary period in chambers in situ, while there was an abrupt increase in bacteria within chambers exposed in the laboratory. A rapid initial decrease was observed in the experimental variation using bottles, accompanied by higher levels of injury inE. coli and reduced expression of plasmid-borne virulence phenotypes inY. enterocolitica. However, there were no changes in the plasmid profiles of either organism throughout the 21-day duration of the experiments. In addition, the survival and injury of pathogenic and nonpathogenic strains of both test bacteria was very similar with aquatic exposure. These results suggest that the response of enteric bacteria in aquatic environments is influenced by experimental design as well as other factors and that the comparison of survival data should only be attempted when similar methods are used.

Production of toxic antigens in dialyzed cultures of microorganisms

Data on the production of clostridial toxins in dialyzed cultures are summarized. Principal modifications of this cultivation technique suitable for both research and production are shown. If toxins are released from the cells by autolysis (neurotoxins of Clostridium tetani, C. botulinum; lethal factors of C. novyi and C. sordellii), a 10-fold increase of the antigen concentration in filtrates of dialyzed cultures is found in comparison with normal cultures. If toxins are excreted already during growth (lethal factors of C. perfringens type A, C. septicum), the positive effect of the technique is less significant. A dialyzed culture ensures a well-balanced production of toxic filtrates that contain highly concentrated, relatively pure and strongly immunogenic antigens.

In vitro amplification of toxic shock syndrome toxin-1 by intravaginal devices

Super-absorbent tampons and an exotoxin of Staphylococcus aureus have been associated with the recent emergence of toxic shock syndrome (TSS). In the majority of cases, when a TSS strain of S. aureus was cultivated in the presence of various tampons and a contraceptive sponge, increased amounts of toxic shock syndrome toxin-1 (TSST-1) were observed to be produced into the blood medium by the bacterium. The amplification of toxin by these products adds support to the epidemiologic data in establishing the causal link between tampons and TSS.

Survival of natural sewage populations of enteric bacteria in diffusion and batch chambers in the marine environment

The survival of natural populations of Escherichia coli and enterococci in sewage was measured in large-volume diffusion chambers in an estuary and a salt marsh. The 5-liter chambers, with polycarbonate membrane sidewalls, were found to be suitable for up to week-long experiments. Decay rates, measured monthly from February to August 1978, ranged from 0.042 to 0.088 h(-1) (time for 90% of the population to die = 25 to 55 h) for E. coli and 0.019 to 0.083 h(-1) (time for 90% of the population to die = 29 to 122 h) for enterococci and were significantly correlated with temperature. In contrast to the diffusion culture experiments, the decay of E. coli in batch culture did not correlate with temperature. Enterococci survived longer than E. coli in the Narragansett Bay (estuary) experiments, but survived less well in the more eutrophic salt marsh. The effect of light on survival was examined with light/dark experiments and sampling at frequent intervals over the diel cycle. Diel changes in survival were not evident in the Narragansett Bay experiments. E. coli, however, exhibited a diel pattern of growth during the day and death at night in the salt marsh. There was no significant difference in decay rates between light and dark diffusion chambers, nor were decay rates correlated with light intensity. In concurrent batch experiments, survival was significantly greater in the dark for both organisms. These results suggest that the effect of light is complex and that conditions in batch culture may modify the survival of enteric bacteria. Observations made in diffusion chambers may more closely follow the in situ survival of enteric microorganisms.

Quantitative microbiological monitoring of hemodialysis fluids: evaluation of methods and demonstration of lack of test relevance in single-pass hemodialysis machines with automatic dialysate proportioning with reverse osmosis-treated tap water

Two methods for estimating the quantity of microorganisms present in hemodialysis fluid, a blood agar surface-spread plate method and a total-count water tester device impregnated with modified standard plate count agar (Millipore Corp., Bedford, Mass.), were evaluated. Both methods exhibited comparable precision; however, colony counts obtained with the total-count water tester were consistently and unacceptably low. The need for routine quantitative microbiological monitoring of hemodialysis fluids such as that recommended by the American Public Health Association was not supported by the results of this study. Such testing was not of value in predicting untoward reactions for patients undergoing hemodialysis, nor did quantitative testing of hemodialysis fluids identify the buildup of potentially hazardous levels of contamination within hemodialysis systems. Finally, the kinds of organisms found in hemodialysis systems, i.e., gram-negative water-borne bacilli, were elucidated.

In situ and laboratory studies of bacterial survival using a microporous membrane sandwich

A new device and procedure for the study of bacterial survival in an aquatic environment are described. The device uses two appressed presterilized microporous membranes to expose a bacterial cell suspension to the environment at a cell concentration that closely resembles those levels found in natural aquatic ecosystems. The device has been used under laboratory controlled conditions and in situ to study and compare bacterial survival times. In laboratory studies, Escherichia coli and Streptococcus faecalis survived the longest at 12 degrees C, pH 5, and in the presence of iron or calcium ions and cysteine. Cells in mid-stationary growth phase survived longer than those in mid- or late-logarithmic phase, whereas those maintained for a year or more as stock cultures survived for shorter period of time than did recent environmental isolates. In situ studies indicate that 5% of the starting number of E. coli and S. faecalis cells may survive longer than 96 h at 16 degrees C in potable lake water, whereas survival times in polluted lake water were approximately 12 h.

Cage Culture Turbidostat: a Device for Rapid Determination of Algal Growth Rate

The present cage culture turbidostat consists of a growth chamber and a control unit. The microorganisms (photoautotrophic algae) are kept in the growth chamber by porous membranes (pore size 1 to 3 μm) which retain the algae but allow efficient exchange of the growth medium. Flow rate and composition of the medium can therefore be varied independently of algal population density. A reciprocating pumping mode of the medium is introduced to obtain more gentle clearance of membranes than that provided by rotation or stirring in other membrane fermentors. Pulsed light and a light-emitting diode/light-sensitive transistor couple are used to monitor the turbidity of the culture, independent of external light needed for growth. The control unit keeps the turbidity constant by frequent activation of the dilution pump. Theoretical analysis of growth in the turbidostat shows that integrated activation time of the dilution pump is proportional to the growth rate of the organism. Theoretical analysis was also used to determine minimum flow-rate and nutrient concentration of medium to cover the requirement of the algae. Experiments with three different marine diatoms were carried out, and they demonstrated that the growth rate could be determined every hour and that the cultures could be kept at constant turbidity over 10 to 14 days at least.

Expression of Rhizobial Nitrogenase: Influence of Plant Cell-Conditioned Medium

Conditioned medium was obtained from suspension cultures of soybean ( Glycine max L. Merrit) cells after incubating them for 4 to 8 days with rhizobia which were separated from the soybean cells by two dialysis bags, one within another. This conditioned medium from the plant cell side (PCM) of the two membranes was used to elicit and influence nitrogenase activity (acetylene reduction) in rhizobia. When conditions for obtaining PCM from the soybean cell suspension cultures were varied, it could be shown that freshly grown rhizobia were able to induce active compounds in the PCM. These compounds caused acetylene reduction activity in test rhizobia under conditions where control rhizobia, containing various substrates, showed little or no acetylene reduction activity. Rhizobia that were already capable of acetylene reduction could not induce such compounds in the PCM when this was included with test rhizobia. The PCM from soybean cultures was also found to aid the expression of nitrogenase activity in suspension cultures of rhizobia normally associated with either peas, lupins, broad beans, or clovers. This is the first communication indicating nitrogenase activity in freeliving cultures for various species of rhizobia.

Dialysis Continuous Process for Ammonium-Lactate Fermentation of Whey: Mathematical Model and Computer Simulation

A mathematical model was developed to describe a dialysis process for the continuous fermentation of whey lactose to lactic acid, with neutralization to a constant pH by ammonia. In the process, whey of a relatively high concentration is fed into the fermentor circuit at a relatively low rate so that the residual concentration of lactose is low. The fermentor effluent contains ammonium lactate, bacterial cells, and residual whey solids and could be used as a nitrogen-enriched feedstuff for ruminant animals. Only water is fed into the dialysate circuit at a relatively high rate. The dialysate effluent contains purified ammonium lactate and could be converted to lactic acid and ammonium sulfate for industry. The fermentation was specifically modeled as a set of equations representing material balances and rate relationships in the two circuits. Dialysis continuous fermentations, in general, were modeled by combining these equations and by using dimensionless parameters. The generalized model was then solved for the steady state and used to simulate the specific fermentation on a digital computer. The results showed the effects of various material and operational and kinetic parameters on the process and predicted that it could be operated efficiently.

Dialysis Continuous Process for Ammonium-Lactate Fermentation of Whey: Experimental Tests

Laboratory experiments were conducted to validate theoretical predictions describing a dialysis continuous process for the fermentation of whey lactose to ammonium lactate, in which the fermentor contents are poised at a constant pH by adding ammonia solution and dialyzed through a membrane against water. Dried sweet-cheese whey was rehydrated to contain 230 mg of lactose per ml, supplemented with 8 mg of yeast extract per ml, charged into a 5-liter fermentor without sterilization, adjusted in pH (5.3) and temperature (44°C), and inoculated with Lactobacillus bulgaricus. The fermentor and dialysate circuits were connected, and steady-state conditions were established. A series of such conditions was managed nonaseptically for 94 days to study the process and to demonstrate efficiency and productivity. As time progressed, the fermentation remained homofermentative and increased in conversion efficiency, although membrane fouling necessitated dialyzer cleaning about every 4 weeks. With a retention time of 19 h, 97% of the substrate was converted into products. Relative to nondialysis continuous or batch processes for the fermentation, the dialysis continuous process enabled the use of more concentrated substrate, was more efficient in the rate of substrate conversion, and additionally produced a second effluent of less concentrated but purer ammonium lactate.

Comparison ofin Situ andin Vitro survival ofCandida albicans in seawater

The survival in seawater of several laboratory and field isolates ofCandida albicans was investigated. Initial studies were madein vitro (flasks) to confirm previous reports. Frequent sampling of viable cells showed that flask experiments, even repeated, produced varied patterns of survival in this closed system. As an alternative, multiple experiments were run in untreated seawater in dialysis bags and plexiglas chambers at ambient temperature (17‡ to 22‡C) in flowing seawater. Die-off rates of all cultures tested in dialysis bags were very rapid in the first day and may have been related to high levels of dissolved organic carbon in the tubing. Distilled water-or acid-washed bags did not yield significantly higher survival rates in all cases. When plexiglas chambers closed with Nuclepore membranes were used, survival rates decreased to 5% to 15% of the original population after 6 days. Chamber data were more uniform and represented approximately a twofold increase in survival over that shown previously inin vitro (flask) studies. Some evidence was obtained in all three test systems for the greater survival rate of a field isolate ofC. albicans compared with that noted for a laboratory (ATCC) strain. The results are considered to more accurately depict the survival ofC. albicans in summer temperate recreational waters.

Dialysis technique for containment of microbial populations inoculated into food systems

A technique utilizing dialysis tubing was developed for the containment of microbial populations introduced into a food system. The entrapment of the inoculum was accomplished while reducing interference with interactions between the sample and the surrounding environment.

Quantitative requirements for exponential growth of Alcaligenes eutrophus

Quantitative nutrient requirements for unrestricted autotrophic growth of Alcaligenes eutrophus were determined. Minimum saturating concentrations of Mg2+, SO42-, PO43-, Fe3+, and Na2+ for an optical density increase of 2 were 10(-4) M 8 X10(-5) M, 5 X 10(-4) to 6 X 10(-4) M, 10(-5) M, and 10(-7) to 2 X 10(-7) M, respectively. Trace metal requirements for cobalt, chromium, and copper were also demonstrated, but minimum concentrations could not be determined because other reagents contributed a high background of these metals. Under certain conditions an apparent response to zinc was observed, although other experiments suggest the zinc salt contained another metal that was required for growth. Poly-beta-hydroxybutyrate biosynthesis was shown to be initiated by a magnesium or sulfate deficiency as well as by a nitrogen or phosphate deficiency.

Survival of bacteria in seawater using a diffusion chamber apparatus in situ

A microbiological survival chamber for in situ environmental studies involving microorganisms of public health significance was developed. The autoclavable chamber was provided with a supportive base for proper flow orientation and a battery-powered stirring mechanism for continuous internal agitation. The performance of the chamber and its ancillary units was evaluated in estuarine waters by diffusion studies and survival tests with eight species of bacteria isolated from environmental sources. Polycarbonate filter membranes were found superior to cellulosic filter membranes. Continuous mixing enhanced diffusion and ensured uniform cell suspension. Salmonella enteritidis and Klebsiella pneumoniae exhibited somewhat greater viability than Escherichia coli under similar conditions. Of three indicator organisms tested, Streptococcus faecalis was the most persistent. In general, the data obtained indicate the usefulness of the chamber in measurements of microbial survival in the natural marine environment.

In situ morphology of nitrifying-like bacteria in aquaculture systems

The in situ microbiota from several aquaculture facilities with active nitrification was examined by transmission electron microscopy of thin sections for the presence of bacteria that contained intracytoplasmic membranes characteristic of the nitrifying bacteria. Colonies of bacteria with the cellular morphology of a species of Nitrosomonas were found to be present in both the culture water and in the biological filter slime of a freshwater chinook salmon (Oncorhynchus tshawytscha) culture system. bacteria in the water possessed the normal nitrosomonas type of ultrastructure, whereas similar bacteria in the slime had an aberrant morphology due to multiple invaginations of the cell wall and cyto-membranes and a significantly greater number of ribosomes. These nitrosomonas-like bacteria lysed during enrichment in commonly used media. Bacteria with the morphology of species of Nitrosomonas and Nitrosococcus were also observed in colonies in the surface slimes of marine culture systems for striped bass (Morone saxatilis) and quahaug (Mercenaria mercenaria).

Bioengineering problems connected with the use of conventional and unconventional raw materials in fermentation. A review

Some bioengineering problems connected with the use of conventional and unconventional raw materials in fermentation research and industry are reviewed. They include the effect of the physical state of different substrates (solid, liquid, gaseous) and considerations of physico-chemical processes, especially the identification of limiting steps. A new concept of classification of fermentors with respect to the macromixing properties is suggested and its applicability for different substrates is considered.

Influence of environmental stress on enumeration of indicator bacteria from natural waters

The problems associated with recovery of pure cultures of Escherichia coli and Streptococcus faecalis from stream environments were examined utilizing membrane filter chambers. It was observed that upon exposure to the aquatic environment a significant proportion of cells lost their ability to produce colonies on a selective medium, yet retained this capability on a nutritionally rich, nonselective medium. Discrepancies in colony-forming units between nonselective and selective media indicated that a substantial portion of bacterial cells may become physiologically injured due to the environmental stress imposed by the aquatic environment. The extent of injury was observed to vary considerably among the eight different stream environments, since the amount of injury was not uniform for all types of water environments examined. It was observed that the injury acquired by a population of E. coli, during exposure to the aquatic environment, could be rapidly repaired in a nutritionally rich, nonselective medium. As the injured population of cells was exposed to the rich, nonselective broth, increasing proportions of cells were able to repair themselves such that they became insensitive to inhibitory agents in selective media.

Factors that influence microbial contamination of fluids associated with hemodialysis machines

Studies were conducted on the microbiological quality of fluids associated with different types of dialysis systems located in six dialysis centers and 14 homes. Included were (i) single-pass systems employing either parallel flow (Kiil or Gambro) or capillary cartridge dialyzers and (ii) recirculating single-pass and batch recirculating systems using coil dialyzers. Microbiological assays were performed on the water used to prepare dialysis fluid, the concentrated dialysate, and either pre- and postdialyzer dialysate (single-pass systems) or the dialysate contained in storage reservoirs and recirculating cannisters (recirculating systems). The levels of microbial contamination consisting of gram-negative bacteria were directly related to the type of dialysis system, method of water treatment, distribution system, and in some instances, the type of dialyzer. Recirculating single-pass and batch recirculating systems consistently contained significantly higher levels of contamination than single-pass systems. These results were directly related to the design of recirculating systems which permits carbon- and nitrogen-containing waste products dialyzed from the patient to accumulate, be used as nutrients by microorganisms, and subsequently allow for 2- to 4-log increases in contamination levels during a dialysis treatment. In contrast, levels of contamination in single-pass machines were related more to the quality of the water used to prepare dialysis fluid and the adequacy of cleaning and disinfection procedures than to the design of the system.

Hemodialysis culture of Serratia marcescens in a goat-artificial kidney-fermentor system

Hemodialysis was employed to simulate in vivo conditions for growth in mammalian blood, but without phagocytosis, by using the goat and Serratia marcescens as a host-parasite model. The blood stream was shunted surgically via prosthetic tubing from a carotid artery through the hollow-fiber membranes in an artificial kidney hemodialyzer and back into a jugular vein. The dialysate solution concurrently was pumped from a modular fermentor through the hemodialyzer jacket outside of the membranes and back into the fermentor. Hemodialysis between the two circuits was maintained continuously. When equilibrium was attained, bacteria inoculated into the dialysate circuit multiplied first exponentially at the maximal rate and then arithmetically at a lesser rate equally well under aerobic or anaerobic conditions. When a population of about 10(9) viable bacteria/ml was exceeded, the goat reacted acutely with signs of general toxemia, pyrexia, and leukopenia, apparently because of dialyzable toxic material produced by the culture. The maximal molecular size of the toxic material was defined relative to a rigid globular protein of 15,000 in molecular weight and 1.9 nm in hydrodynamic radius or to a flexible fibrous polyglycol of 5,500 in molecular weight and 2.6 nm in hydrodynamic radius, based on determinations of the membrane porosity threshold for dialysis.

Survival of coliform bacteria in natural waters: field and laboratory studies with membrane-filter chambers

Chambers with membrane-filter side walls were designed for studies of the survival of coliform bacteria in natural and artificial waters. Experiments were carried out in the field and in the laboratory. The initial uptake rate of inorganic ions, total carbon, and glucose into the chamber was greater than twice as fast as the accumulation of each into dialysis tubing. When the survival of a water-isolated fecal coliform bacterium was examined in two adjacent mountain streams, it was found that the organism persisted longer in Bozeman Creek than in Middle Creek. These data may be a reflection of the water chemistry because the concentration of inorganic constituents of the former was greater. Laboratory studies of the survival of a fecal coliform bacterium in artificial and natural water with continuous flow were used to determine the effect of chemical composition, temperature, and pH. The relation of this type of data to the use of fecal coliform bacteria as indicators of health hazard in water is discussed.

Clostridium perfringens. I. Sporulation in a biphasic glucose-ion-exchange resin medium

A biphasic culture medium suitable for cultivation and sporulation of Clostridium perfringens, C. botulinum, and C. sporogenes was devised. The medium designed for use in a disposable, compartmented, plastic film container contained peptones, yeast extract, minerals, an anion exchange resin, and glucose in 4% agar as the solid phase and (NH(4))(2)SO(4) and 0.1% agar as the liquid phase. With the biphasic system, it was not necessary to use active cultures as inocula. Growth was at least equal to that obtained in conventional media, and spore production of 9 out of 12 strains of C. perfringens equalled or usually exceeded that of conventional media.

The diffusion capsule, a novel device for the addition of a solute at a constant rate to a liquid medium. Its application to metabolic regulation

The diffusion capsule consists of a cylindrical container that can be completely filled with a solution and sealed with a small semi-permeable membrane at one end. In use, the capsule is immersed in an agitated liquid. Experiments on concentrated solutions in the capsule showed that, contrary to diffusion theory, the rate of diffusion of solute (sugars or amino acids) out of the capsule remained virtually constant until about 65% of the solute had diffused out of the capsule. Thus the device has been used to maintain constant material feed rates for periods exceeding 30h. The capsule is a simple and compact substitute for a pump and is superior to a pump for small feed rates in many applications. The capsule greatly extends the scope of the shake-flask culture technique for micro-organisms in that substrate-limited growth, possibly the aspect of greatest interest, is readily achieved simply by dropping in the flask a capsule containing the substrate. Diffusion feed should facilitate study of the metabolism of toxic substrates: also it is likely to provide an improved means for supplying a pulse of tracer to a culture.