Protectants used in the cryopreservation of microorganisms

Viability of commercial wine yeasts during freezer storage in glycerol-based media

Glycerol-based medium (BM) with and without the addition of 1 g/L ascorbic acid (Asc) and/or 100 mg/L (+/-)-catechin (Cat) was tested for the storage of three commercial wine yeasts at -20 degrees C. The medium supplemented with Asc was also used to store 706 strains to verify the maintenance of the liquid state. A decline in survival throughout the storage period was observed. The media containing Asc maintained viability better than the other three. The BM caused a loss of viability of 7 orders for one strain and of 6 orders for the other two. All three strains exhibited a loss of viability of 4 orders when stored in BM+Asc. Two strains decreased viability by 5 orders while one strain by 4 orders, when stored in BM+Cat. Two strains decreased viability by 6 orders while one strain by 5 orders, when stored in BM+Asc+Cat. Regarding the physical state of the medium tested on 706 yeast strains, three cases were observed: completely liquid (56.5 %), liquid with only the upper part frozen (40.4 %) without involving the yeast biomass settled at the bottom, and completely frozen (3.12 %). It is practicable to prepare a BM that remains liquid at -20 degrees C enhancing yeast viability when Asc is added as cryoprotectant.

Risk of contamination of germplasm during cryopreservation and cryobanking in IVF units

Cryopreservation of sperm, embryos and, more recently, oocytes plays an important and increasing role in assisted reproduction, due to improvements of old, and introduction of new technologies. In parallel, concerns are increasing about the technical and biological safety of these procedures. However, published data regarding the confirmed or theoretical hazards of these procedures are sparse and sometimes contradictory. The purpose of this review will summarize data and opinions about one of the most disputed risks, the potential hazard of contamination and disease transmission through cryopreservation. Special attention is concentrated on the weak points of the technology including open vitrification systems, sterilization of liquid nitrogen and safety of commonly used storage tanks including straws and cryovials. Suggestions are also made for practical measures to avoid these dangers while preserving the benefits and perspectives of new cryopreservation technologies.

Effect of the fermentation pH on the storage stability of Lactobacillus rhamnosus preparations and suitability of in vitro analyses of cell physiological functions to predict it

AIMS

To investigate how cell physiological functions can predict the stability of freeze-dried probiotics. In addition, the effect of the fermentation pH on the stability of probiotics was investigated.

METHODS AND RESULTS

Fermenter-grown (pH 5.8 or 5.0) Lactobacillus rhamnosus cells were freeze-dried and their survival was evaluated during storage at 37 degrees C, in apple juice and during acid [hydrochloric acid (HCl) and malic acid] and bile exposure. Cells grown at pH 5.0 were generally coping better with acid-stress than cells grown at pH 5.8. Cells were more sensitive to malic acid compared with HCl. Short-term stability results of Lact. rhamnosus cells in malic acid correlated well with the long-term stability results in apple juice, whereas the results of cell membrane integrity studies were in accordance with bile exposure results.

CONCLUSIONS

Malic acid exposure can prove useful in evaluating the long-term stability of probiotic preparations in apple juice. Fermentation at reduced pH may ensure a better performance of Lact. rhamnosus cells during the subsequent acid-stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

The beneficial effect of lowered fermentation pH to Lact. rhamnosus stability during storage in apple juice and the usefulness of malic acid test in predicting the stability were shown.

Microencapsulation of probiotic strains for swine feeding

Probiotics are live microorganisms which have health-promoting attributes. These bacteria must overcome biological barriers, including acid in the stomach and bile in the intestine to exert beneficial effects. The encapsulation consists in a provision of an outer layer to protect the core material from damage. Microencapsulating in calcium alginate, nowadays, is being used to bacteria immobilization owing to its easy handling, nontoxic nature, and low cost. The aims of this study were to improve the microencapsulating method for probiotic bacteria and to investigate whether the material used as coating, afford an increase on strain survival under simulated gastrointestinal conditions. Lactic acid bacteria used in this work were isolated from feces of young and healthy pigs and they were selected because of their probiotic properties. Our results showed that the optimal encapsulation process was achieved using 1 : 1 (v/v) 20% non fat milk cell suspension mixed with 1.8% sodium alginate solution. Alginate capsules hardening was carried out using 0.1 m calcium chloride solution for 30 min. This microencapsulating technique could protect the probiotic bacteria against gastric environment, allowing viable cells get to the intestinal tract. So it could be a useful way to deliver these beneficial bacteria to host.

Serum-free solutions for cryopreservation of cells

With the development of cell-based assays and therapies, the purity of reagents used to grow and maintain cells has become much more important. In particular, the use of fetal calf serum for culturing cells presents a direct path for potential contamination of cell cultures. In recent years, much research has focused on the development of serum-free culturing systems, not only to alleviate difficulties due to availability and cost of fetal calf serum but also to prevent the transmission of potentially fatal diseases to human patients. Additionally, methods need to be developed for long-term storage of cell stocks that also reduce the risk of exposure to harmful diseases. As most methods employ fetal calf serum in their freezing formulations, solutions that avoid the use of fetal calf serum while providing equivalent or better recovery of cells upon thawing would be ideal. In this study, two vascular cell lines have been cryopreserved as adherent cell populations in two widely used cryoprotectants, dimethyl sulfoxide and 1,2-propanediol, and two vehicle solutions, Euro-Collins and Unisol-cryoprotectant vehicle specifically formulated for the maintenance of cell homeostasis at temperatures below 37 degrees C. The addition of serum to these formulations was also evaluated to determine if its presence provided any additional benefit to the cells during cryopreservation. The results demonstrated that using vehicle solutions designed for lower temperatures produced viable cells that retained cell population viability values up to 75% of unfrozen controls. These results also demonstrated that including serum in the formulation provided no additional benefit to the cells and in some cases actually produced lower cell viability after cryopreservation. In conclusion, the development of solutions designed for low-temperature storage of cells provides a viable alternative to more conventional cryopreservation protocols and eliminates the necessity of including serum in these formulations.

Efficient Cryopreservative Conditions for Cultivated Limbal and Conjunctival Epithelial Cells

PURPOSE

To examine the effects of cryopreservation on the viability of cultivated corneal limbal and conjunctival epithelial cells and to evaluate the optimal conditions for cryopreservation.

METHODS

The cultivated human limbal epithelial cells (HLECs) were stored in media including 20%, 50%, and 90% fetal bovine serum (FBS) and 10% dimethyl sulfoxide (DMSO) at -196 degrees C for 1 week. The cultivated rabbit conjunctival epithelial cells were stored in 10%, 20%, and 50% FBS with 10% glycerol or DMSO as a cryoprotectant at -196 degrees C for 1 week. After thawing, cell viability was assessed using the trypan blue vital staining and 3-[4,5-dimethylthiazol-2-yl]-2,5-dephenyl tetrazolium bromide (MTT) assay. Immunofluorescent staining was performed with cytokeratin 3/12 antibody. Colony-forming efficiency (CFE) was evaluated 2 weeks after culture.

RESULTS

HLECs cryopreserved with 50% FBS showed the highest cell viability, whereas those with 20% FBS revealed the lowest survival rate (87.1% +/- 0.8% and 79.8% +/- 4.01%, respectively; P = 0.030). CFE of HLECs was 2.13 +/- 1.35%, 2.31 +/- 2.23%, and 1.94 +/- 0.72% in cells with 20%, 50%, and 90% FBS, respectively (P > 0.05). For conjunctival epithelial cells, the cell viability was the highest with 50% FBS and 10% glycerol (95.0% +/- 4.27%), and the lowest survival rate was observed in the condition of 10% FBS and 10% DMSO (80.0% +/- 5.49%). CFE of cryopreserved conjunctival epithelial cells was 14.1% +/- 1.9% in cells with 20% FBS and glycerol and 13.5% +/- 2.0% in those with 20% FBS and DMSO (P > 0.05). HLECs expressed CK3/12 after cryopreservation in all conditions examined.

CONCLUSIONS

The best results were yielded by 50% FBS for cell viability in HLECs. Glycerol seems to be superior to DMSO in cell viability of the rabbit conjunctival epithelium after cryopreservation.

Effect of intracellular trehalose in Cryptococcus laurentii and exogenous lyoprotectants on its viability and biocontrol efficacy on Penicillium expansum in apple fruit

AIMS

To improve viability and biocontrol efficacy of Cryptococcus laurentii after freeze drying and in subsequent storage.

METHODS AND RESULTS

Viability of C. laurentii was improved after freeze drying and in subsequent storage at 4 or 25 degrees C by using skimmed milk (SM) and sugars (glucose, galactose, sucrose and trehalose) as protectants. Sugars and SM mixed together showed better protection than when they were used separately. Citric acid used as carbon source could induce accumulation of intracellular trehalose in the yeast. The yeast cells with high trehalose level (HT cells) had higher viability than those with low trehalose level (LT cells) after freeze drying and storage for 90 days. After storage for 90 days at 4 degrees C, the HT cells plus SM and sugars as protectant showed a similar biocontrol effect against blue mould rot in apple fruit caused by Penicillium expansum as fresh cells.

CONCLUSIONS

Increasing intracellular trehalose content of C. laurentii and adding exogenous protectant (sugars + SM) could improve its viability and maintain its biocontrol efficacy.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results have a potential value for commercial application of C. laurentii.

Effect of sphingosine and phorbol-12-myristate-13-acetate on the growth and dimethylsulfoxide-induced differentiation in the insect trypanosomatid Herpetomonas samuelpessoai

We investigated the effect of two modulators of protein kinase C, sphingosine and phorbol-12-myristate-13-acetate (PMA), on the growth and dimethylsulfoxide (DMSO)-induced differentiation in Herpetomonas samuelpessoai. Sphingosine did not stimulate the transformation of undifferentiated-promastigotes in differentiated-paramastigotes. PMA alone or in association with DMSO increased the number of paramastigotes in comparison to control cells. DMSO inhibited the parasite growth (35%) and several unusual morphological features resembling aberrant cell division were observed. Sphingosine did not significantly reduce the growth in contrast to PMA. Collectively, our results demonstrated that the reduction of the proliferation translates in an increase of the differentiation rate in the insect trypanosomatid H. samuelpessoai.

Optochin resistance in Streptococcus pneumoniae induced by frozen storage in glycerol

Susceptibility to optochin is frequently the only test used to differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci isolated from clinical specimens. The current study shows that storage of S. pneumoniae isolates in tryptic soy broth containing 15% glycerol at -70 degrees C can lead to optochin resistance. This optochin resistance was sometimes reversible by growing the bacteria in broth. Optochin-susceptible and optochin-resistant variants of individual S. pneumoniae isolates have similar pulsed-field gel electrophoresis pattern. However, optochin-resistant S. pneumoniae isolates exhibit differences in ultrastructure compared with optochin-susceptible variants. This study demonstrates that the frozen storages of S. pneumoniae in glycerol may affect the optochin phenotype. Thus, this characteristic should not be the only one used for identification of S. pneumoniae after frozen storage of isolates.

A simple and rapid method for cryopreservation of Trichomonas vaginalis

A pellet freezing method, one type of rapid freezing protocol, was established for Trichomonas vaginalis. As cryoprotectants, 5-20% dimethylsulfoxide (DMSO), ethylene glycol, propylene glycol, and glycerol were used. Of these, DMSO showed a high protective effect, with a maximum effect at a concentration of 20%. No effect of equilibration time was recognized with any of the cryoprotectants. Therefore, the optimal condition was deemed 20% DMSO without equilibration. The pellet freezing method was also compared with the conventional slow cooling protocol. The survival rate was 73 +/- 8% with the slow cooling protocol and 48 +/- 4% with the pellet freezing method. The delay in growth with the pellet freezing method was no more than 5.4 h compared with the slow cooling protocol, suggesting its validity as a technique for cryopreservation of T. vaginalis.

Glucose improves the in vitro viability of Microsporum canis and Trichophyton mentagrophytes var. mentagrophytes

We describe simple and cost-effective methods using carbohydrates to improve the in vitro viability of dermatophytes. Glucose and sucrose in different concentrations (3, 6, 9 and 12%) were used to maintain fifteen strains of M. canis and T. mentagrophytes var. mentagrophytes at 4 and -20 degrees C. The strains were phenotypically analyzed before storage and reevaluated at 1, 3, 6 and 9 months. At 1 and 3 months, any alterations in the viability or phenotype pattern of the stored strains were noted. At 6 months, both dermatophytes were 100% viable, when preserved in glucose (3, 6, 9 and 12%) at -20 degrees C. All T. mentagrophytes strains were also viable in sucrose (12%), at 4 degrees C and -20 degrees C. However, sucrose failed to improve the viability of M. canis at both temperatures. At 9 months, the higher viabilities without pleomorphism were seen for both dermatophytes preserved in glucose (9 and 12%) at -20 degrees C.

Effects of cryoprotectant agents and freezing protocol on motility of black-lip pearl oyster (Pinctada margaritifera L.) spermatozoa

Gamete cryopreservation techniques have been applied to several bivalve mollusc species. However, research activity in this area has primarily focused on cryopreserving gametes from edible oysters (Ostreiidae). Few studies have examined the effect of cryoprotectants and freezing protocols in the preservation of spermatozoa from cultured pearl oysters (Pteriidae). Pearl oyster producers are increasingly looking towards the development of improved family lines and, as a consequence, the ability to cryopreserve gametes would bring about significant benefits to the cultured pearl industry. In response to this need, we evaluated the effect of three cryoprotectant additives (CPA) on motility of spermatozoa from the black-lip pearl oyster, Pinctada margaritifera. These additives have previously been used to cryopreserve gametes of other bivalve species. The following CPA mixtures were evaluated: (1) 0.45M trehalose and 0, 0.64, 1.02 and 1.53 M dimethyl sulfoxide (Me(2)SO); (2) 0.2M glucose and 2M Me(2)SO and (3) 1.31 M propylene glycol (PG). The effects of four different freezing protocols on motility of P. margaritifera spermatozoa were also evaluated (slow, medium, medium-rapid and rapid cooling). This study showed that total motility was best retained when spermatozoa were cryopreserved in 0.45 M trehalose and 0, 0.64, 1.02 or 1.53 M Me(2)SO and frozen using slow to medium-rapid cooling rates (2.1-5.2 degrees Cmin(-1)). Rapid freezing through direct plunging of spermatozoa into liquid nitrogen resulted in the lowest overall retention of motility regardless of the CPA additive; however, CPA mixture also influenced retention of motility, with 0.2M glucose in 2M Me(2)SO and 1.31 M PG retaining the lowest levels of motility for the CPAs evaluated.

Fetal calf serum versus human serum: ultrastructural evaluation of protein support influence on human ovarian tissue cryopreservation

The aim of this study was to examine the effect of the different protein supports in the cryopreservation solution on improving human ovarian tissue preservation after frozen-thawed procedures. Biopsies of ovarian cortical tissue were obtained from 14 subjects. All specimens were cryopreserved using a slow freezing/rapid thawing method in a solution consisting of propanediol and sucrose in different proportions of 3 protein supports: 30% human serum (HS) (solution A), 20% HS (solution B), or 20% fetal calf serum (solution C). After thawing, 191 follicles and a total of 70 samples were analyzed using transmission electron microscopy (TEM). The post-thaw preservation rate of the follicles in solution A was significantly higher with respect to solution C (p < 0.05). Unlike the follicles, the stromal cell morphology was not affected by any of the solutions investigated. By comparing stromal morphology and the patient age, it was found that HS better preserved the tissue in patients over 20 years of age with respect to younger ones, which showed a wider variability in ovarian preservation. TEM evaluation showed that 30% HS is more suitable for human ovarian tissue cryopreservation, and research should be focused on defining cryopreservation protocols specific to young patients.

Single Cystosorus Isolate Production and Restriction Fragment Length Polymorphism Characterization of the Obligate Biotroph Spongospora subterranea f. sp. subterranea

ABSTRACT Spongospora subterranea f. sp. subterranea causes powdery scab in potatoes and is distributed worldwide. Genetic studies of this pathogen have been hampered due, in part, to its obligate parasitism and the lack of molecular markers for this pathogen. In this investigation, a single cystosorus inoculation technique was developed to produce large amounts of S. subterranea f. sp. subterranea plasmodia or zoosporangia in eastern black nightshade (Solanum ptycanthum) roots from which DNA was extracted. Cryopreservation of zoosporangia was used for long-term storage of the isolates. S. subterranea f. sp. subterranea-specific restriction fragment length polymorphism (RFLP) markers were developed from randomly amplified polymorphic DNA (RAPD) fragments. Cystosori of S. subterranea f. sp. subterranea were used for RAPD assays and putative pathogen-specific RAPD fragments were cloned and sequenced. The fragments were screened for specificity by Southern hybridization and subsequent DNA sequence BLAST search. Four polymorphic S. subterranea f. sp. subterranea-specific probes containing repetitive elements, and one containing single copy DNA were identified. These RFLP probes were then used to analyze 24 single cystosorus isolates derived from eight geographic locations in the United States and Canada. Genetic variation was recorded among, but not within, geographic locations. Cluster analysis separated the isolates into two major groups: group I included isolates originating from western North America, with the exception of those from Colorado, and group II included isolates originating from eastern North America and from Colorado. The techniques developed in this study, i.e., production of single cystosorus isolates of S. subterranea f. sp. subterranea and development of RFLP markers for this pathogen, provide methods to further study the genetic structure of S. subterranea f. sp. subterranea.

Preservation of micro-organisms by drying; A review

The preservation of micro-organisms by different drying methodologies has been used for decades. Freeze drying in particular is the preferred method for transporting and storing vast culture collections of micro-organism strain types. The literature on drying and preserving micro-organisms is extensive, but is often specific to one particular strain. This review attempts to draw some similar concepts and findings together in one paper, to compare different drying techniques, with specific reference to microorganisms. The main topics covered are cell growth phases and concentration, inducing drying tolerance in microbial cells, drying methods, rehydration of dried cells and packaging and storage conditions. Also, particular attention has been paid to the use of freeze drying and the protective matrices used to improve microbial cell viability after drying.

Fibres as carriers for Lactobacillus rhamnosus during freeze-drying and storage in apple juice and chocolate-coated breakfast cereals

The capability of different fibre preparations to protect the viability and stability of Lactobacillus rhamnosus during freeze-drying, storage in freeze-dried form and after formulation into apple juice and chocolate-coated breakfast cereals was studied. In freeze-drying trials wheat dextrin and polydextrose proved to be promising carriers for the L. rhamnosus strains: both freeze-drying survival and storage stability at 37 degrees C were comparable to the control carrier (sucrose). Using apple fibre and inulin carriers resulted in powders with fairly good initial freeze-drying survival but with poor storage stability at 37 degrees C. When fresh L. rhamnosus cells were added into apple juice (pH 3.5) together with oat flour with 20% beta-glucan the survival of the cells was much better at 4 degrees C and at 20 degrees C than with sucrose, wheat dextrin and polydextrose, whereas with freeze-dried cells no protective effect of oat flour could be seen. The stability of freeze-dried L. rhamnosus cells at 20 degrees C was higher in chocolate-coated breakfast cereals compared to low pH apple juice. Similar to freeze-drying stability, wheat dextrin and polydextrose proved to be better carriers than oat flour in chocolate-coated breakfast cereals. Regardless of their differing capability to adhere to fibre preparations the two L. rhamnosus strains studied gave parallel results in the stability studies with different carriers.

Effect of the cryopreservation conditions on the viability of the rumen ciliate Diploplastron (Metadinium) affine

AIMS

To study the viability of Diploplastron (Metadinium) affine after its cryopreservation at two cooling rates, and the effect of procedure conditions on viability.

METHODS AND RESULTS

There were differences in viability between cooling rates (1 and 4 degrees C min(-1)) at 15 or 5 degrees C, but not after thawing. When the equilibrium temperature (25 or 5 degrees C), the cryopreservant (glycerol or dimethyl sulfoxide [DMSO]) and the use of membrane protector were tested, there were no differences caused by the cryopreservant or the membrane protector. However, the equilibrium at 25 degrees C increased the viability (P = 0.005) compared with 5 degrees C.

CONCLUSIONS

Viability after thawing was 0.10-0.19. Adding the cryopreservant (either glycerol or DMSO) at 25 degrees C instead of 5 degrees C improves viability of D. affine after thawing.

SIGNIFICANCE AND IMPACT OF THE STUDY

Conditions of cryopreservation are largely dependent on the species of rumen protozoa. Number of viable cells after thawing would indicate the possibility of culture recovery for D. affine.

Involvement of two specific causes of cell mortality in freeze-thaw cycles with freezing to -196 degrees C

The purpose of this study was to examine cell viability after freezing. Two distinct ranges of temperature were identified as corresponding to stages at which yeast cell mortality occurred during freezing to -196 degrees C. The upper temperature range was related to the temperature of crystallization of the medium, which was dependent on the solute concentration; in this range mortality was prevented by high solute concentrations, and the proportion of the medium in the vitreous state was greater than the proportion in the crystallized state. The lower temperature range was related to recrystallization that occurred during thawing. Mortality in this temperature range was increased by a high cooling rate and/or high solute concentration in the freezing medium and a low temperature (less than -70 degrees C). However, a high rate of thawing prevented yeast mortality in this lower temperature range. Overall, it was found that cell viability could be conserved better under freezing conditions by increasing the osmotic pressure of the medium and by using an increased warming rate.

Cryopreservation of Holospora undulata, a bacterial parasite of the ciliate Paramecium caudatum

We investigated cryopreservation of horizontal transmission stages of Holospora undulata, a micronucleus-specific bacterial parasite of Paramecium caudatum. Unlike in previous studies on related Holospora species, protocols using glycerol as cryoprotectant failed entirely. In contrast, freezing with dimethyl sulfoxide (Me2SO) conserved infectiousness of nearly all replicate inocula, although infection success was considerably lower than that of fresh inocula. Infection probability was enhanced by increasing the Me2SO concentration from 5 to 10%, and by freezing at -196 degrees C rather than -80 degrees C. Prolonged storage of up to 3 months had no significant effect on the viability of the inocula.

Effect of protective agents, freezing temperature, rehydration media on viability of malolactic bacteria subjected to freeze-drying

AIMS

The effects of protective agents, rehydration media and freezing temperature on the viabilities of Lactobacillus brevis and Oenococcus oeni H-2 when subjected to freeze-drying were investigated.

METHODS AND RESULTS

Several protectants and rehydration media were tested to improve the survival after freeze-drying. The cells were also frozen at -65 and -20 degrees C to check the effect of freezing temperature on the viability.

CONCLUSIONS

The best protectant and rehydration medium to obtain the highest viability after freeze-drying varied with the species of bacteria. Yeast extract (4.0%) and sodium glutamate (2.5% ) gave maximum viability of L. brevis and O. oeni (67.8% and 53.6% respectively). The highest survival of L. brevis and O. oeni were obtained when rehydrated with 10% sucrose and MGY medium respectively. When the bacterial cells were frozen quickly (-65 degrees C) than slowly (-20 degrees C), L. brevis and O. oeni both showed increased viability after freeze-drying.

SIGNIFICANCE AND IMPACT OF THE STUDY

The viabilities of L. brevis and O. oeni after freeze-drying were shown to be strain specific and dependent on protective agents, rehydration media and freezing temperature.

Influence of fermentation time, cryoprotectant and neutralization of cell concentrate on freeze-drying survival, storage stability, and acid and bile exposure of Bifidobacterium animalis ssp. lactis cells produced without milk-based ingredients

AIMS

To investigate the stability of Bifidobacterium animalis ssp. lactis VTT E-012010 (=Bb-12) during freeze-drying, storage and acid and bile exposure. The effect of harvesting time and composition and pH of the cryoprotectant on the survival was evaluated. The procedure was performed by using a milk-free culture medium and cryoprotectants to produce cells for nonmilk-based applications.

METHODS AND RESULTS

Bifidobacterial cells were grown in fermenters in general edible medium for 15 or 22 h. The cell mass was freeze-dried either as non-neutralized or neutralized using sucrose, betaine or reconstituted skim milk (control) as cryoprotectants. For stability studies freeze-dried powders were stored at 37, 5 and -20 degrees C for 2-6 months. In addition, acid and bile tolerance of the powders was tested. Sucrose-formulated B. animalis ssp. lactis preparations had an excellent stability during storage at refrigerated and frozen temperatures for 5-6 months. They also had a good survival during storage at 37 degrees C for 2 months as well as during exposure to pH 3 and 1% bile acids. No difference was observed between 15 and 22 h grown cells or between non-neutralized and neutralized cells. Betaine proved to be a poor cryoprotectant compared with sucrose.

CONCLUSIONS

Fermentation time and neutralization of cell concentrate before freeze-drying had no impact on the storage stability and bile and acid tolerance of freeze-dried bifidobacterial cells. The nonmilk-based production protocol using sucrose as a cryoprotectant yielded powdery preparations with excellent stability in adverse conditions (storage at elevated temperatures and during acid and bile exposure).

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that it is feasible to develop nonmilk-based production technologies for probiotic cultures. This provides new possibilities for the development of nondairy-based probiotic products.

Bio-banking in microbiology: from sample collection to epidemiology, diagnosis and research

Millions of biological samples, including cells of human, animal or bacterial origin, viruses, serum/plasma or DNA/RNA, are stored every year throughout the world for diagnostics and research. The purpose of this review is to summarize the resources necessary to set up a bio-banking facility, the challenges and pitfalls of sample collection, and the most important techniques for separation and storage of samples. Biological samples can be stored for up to 30 years, but specific protocols are required to reduce the damage induced by preservation techniques. Software dedicated to biological banks facilitate sample registration and identification, the cataloguing of sample properties (type of sample/specimen, associated diseases and/or therapeutic protocols, environmental information, etc.), sample tracking, quality assurance and specimen availability. Bio-bank facilities must adopt good laboratory practices and a stringent quality control system and, when required, comply with ethical issues.

Cryopreservation of brain mitochondria: a novel methodology for functional studies

Often, comparative studies involving large number of animals or human post-mortem tissue samples are precluded, especially those requiring structurally and functionally intact cells and/or organelles. The ability to 'bank' such samples for storage and restore or 'reanimate' them at a later time without causing damage to the structure and/or function becomes imperative. However, to date, such attempts have produced conflicting results. We here demonstrate for the first time that isolated rat brain mitochondria can be successfully cryopreserved and restored for later use. We added a well characterized cryoprotectant 10% (v/v) dimethyl sulfoxide (DMSO) to purified rat cortical mitochondria and allowed them to cool at a uniform rate of approximately 1 degree C/min and stored them at -80 degrees C. Freshly isolated as well as reanimated brain mitochondria were analyzed for respiration. Structural integrity of cryopreserved mitochondria was also verified by electron microscopy. Mitochondrial membrane marker levels were assessed along with cytochrome c levels. Intact structure and function of the cryopreserved brain mitochondria observed allows us the opportunity to store mitochondria for longer periods of time as well as perform metabolic studies as needed. This will considerably expand the time-frame required for carrying out functional analysis in large comparative studies.

Non-transmission of bacterial and viral microbes to embryos and semen stored in the vapour phase of liquid nitrogen in dry shippers

Cryopreservation and storage of germplasm is an important factor in the prevention of disease transmission by embryo transfer and artificial insemination. Here we report the results of an investigation on transmission of selected bacterial and viral pathogens by the vapour phase of liquid nitrogen (VPLN) to embryos and semen in dewars designed for short-term storage and transportation of biological specimens. In this study transmission of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, BVDV, and BHV-1 was examined from: (1) contaminated dry shippers to germplasm; (2) between contaminated and non-contaminated cryopreserved germplasm; and (3) between stock culture of pathogenic agents and germplasm. Contaminated and non-contaminated samples of embryos and semen were stored in proximity in the vapour phase LN in open containers for 7 days prior to testing for the presence of microbes. The results showed that there was no cross-contamination from either the contaminated dewars to germplasm or between contaminated and non-contaminated samples of embryos and semen during 7 days storage under LN vapours. The outcome of our investigation indicates that VPLN is a safe means for short-term storage of embryos and semen in dry shipper dewars commonly used for transportation of bovine germplasm.

Regeneration of cryoresistance of in vitro rumen ciliate cultures

The purpose of this study was to investigate factors affecting mechanical- and cryo-resistance of the rumen ciliates Entodinium caudatum (E.c.), Entodinium furca monolobum (E.f.m.), Entodinium simplex (E.s.), Diplodinium denticulatum (two clones, D.d.01 and D.d.02), Diploplastron affine (D.a.) and Epidinium ecaudatum forma caudatum (E.e.c.) after long-term in vitro cultivation. Following prolonged in vitro cultivation (more than six months), the ciliates were very sensitive to both centrifugation and 5% (v/v) dimethylsulphoxide, with motility decreased to: 39 and 23% for E.c., 66 and 32% for E.f.m., 46 and 27% for D.d. 01, 64 and 41% for D.a., and 44 and 28% for E.e.c., respectively. Thus, cryopreservation was unsuccessful. The effect of supplementing the ciliate growth medium with rumen fluid, glycine-betaine, proline, myo-inositol, linoleic acid, Sel-Plex or insulin, together with the effect of the source of rumen fluid on ciliate resistance to centrifugation, dimethylsulphoxide and freezing was also tested. The omission of rumen fluid from the growth medium resulted in the loss of cryoresistance after one-month cultivation. Supplementing the growth environment with a combination of glycine-betaine, proline, linoleic acid, Sel-Plex, insulin plus improved quality rumen fluid significantly enhanced survival of the ciliates after the freezing-thawing procedure (from 1 to 33% survival in un-supplemented vs. supplemented for E.c., P<0.01; 4-40% E.f.m., P<0.01; 0-17% D.d., P<0.05; 5-7% D.a. and 4-36% E.e.c., P<0.01).

Experimental microbial contamination and disinfection of dry (vapour) shipper dewars designed for short-term storage and transportation of cryopreserved germplasm and other biological specimens

Cryopreservation, storage and transport of cryopreserved germplasm without the risk of disease transmission is of great concern to animal and human health authorities. Here we report on the efficacy of microbial decontamination of the liquid nitrogen (LN) dry (vapour) shippers used for short-term storage and transportation of germplasm and other biological specimens. Dry shippers containing either a hydrophobic or a non-hydrophobic LN absorbent were experimentally contaminated with high titers of cultures of Pseudomonas aeruginosa, Escherichia coli, Staphylococus aureus, bovine viral diarrhea virus (BVDV) and bovine herpesvirus-1 (BHV-1). Biocidals with broad spectrum antimicrobial activity and gas vapours of formalin and ethylene oxide were used for disinfection of the dewars. Among the biocidals used, treatment with sodium hypochlorite solution, the quaternary ammonium-based disinfectants and peracetic acid were the most effective and useful for dry shippers with a hydrophobic LN absorbent. None of the bacterial or viral microorganisms were detected in samples of semen and embryos stored in dry shippers following their disinfection with these biocides. An application of some other disinfectants, due to their foaming properties or to the permeability of the absorbent hydrophobic membrane (HM) was not effective or may have caused irreversible damage to the LN absorbent. Gas sterilization by ethylene oxide in contrast to formalin was fully effective for both types of dry shippers.

Parasite cryopreservation by vitrification

Parasitic protozoa and helminths and parasitic/vector insects each have distinct requirements for cryopreservation. Most parasitic protozoa respond to cryopreservation stresses similarly to other single cell suspensions, but few species are currently routinely cryopreserved by protocols specifically designed for vitrification. With slow equilibrium cooling, some protozoa osmotically dehydrated by solutes concentrated in the residual unfrozen fraction will survive by vitrifying. Several species of helminths, together with insect embryos cannot be cryopreserved by slow cooling protocols and have an absolute requirement for vitrification. Studies incorporating slow cooling and stepped cooling of both protozoa and helminths, particularly the intraerythrocytic stages of malaria and the schistosomula larvae of Schistosoma mansoni have aided in the design of vitrification protocols for parasites. For helminths, the most widely used cryopreservation protocol, originally successful for cryopreserving S. mansoni schistosomula, consists of the addition of ethanediol in two steps, followed by rapid cooling (approximately 5100 degrees C min(-1)) to -196 degrees C. This technique exploits the temperature-dependent differential in permeability of the cryoprotectant additive (CPA) to first permeate into the organism at 37 degrees C followed by a dehydration-mediated internal CPA increase in concentration resulting from incubation in a second higher CPA concentration at 0 degree C. Samples are rapidly warmed/diluted (approximately 14,000 degrees C min(-1)) to recover the organisms from liquid nitrogen storage. Variations on this technique have also been successful in cryopreserving the larvae and adult worms of filariae, muscle stage larvae of Trichinella spp., the infective stages of gastro-intestinal nematode parasites and insect embryos. Other protocols where the dehydration step precedes CPA addition have been used to cryopreserve entomogenous nematode larvae by vitrification. Techniques that utilize high concentrations of CPA cocktails and slower cooling, developed for the vitrification of mammalian embryos, have been applied to the cryopreservation of parasitic protozoa, but with limited success to date. Where cryopreservation by classical slow cooling methods is possible, vitrification has enhanced the levels of survival obtained. And vitrification has enabled the successful cryopreservation of those parasitic species not able to be cryopreserved by traditional methods. Since a limited number of parasitic organisms has been cryopreserved using vitrification protocols, there is considerable scope for further improvement in the cryopreservation techniques used for many parasitic species.

Preferential interaction of dimethyl sulfoxide and phosphatidyl choline membranes

The interaction free energy of dimethyl sulfoxide (DMSO) and two types phospholipid membranes has been assessed from measurements of vapor pressure. The lipids were phosphatidyl cholines with respectively (14:0/14:0) (DMPC) and (16:0/18:1) (POPC) fatty acid chains. The results were expressed in terms of the iso-osmolal preferential interaction parameter, Gamma(mu1), which remained negative under all experimental conditions investigated here. This shows that water-membrane interactions are more favorable than DMSO-membrane interactions. This condition is known as preferential exclusion of DMSO (or preferential hydration of the membrane), and implies that the local (interfacial) concentration of the solute is reduced compared to the bulk. At room temperature and 1 m DMSO, Gamma(mu1) was -0.3 to -0.4 for both lipids. This corresponds to a sizable reduction in the DMSO concentration in a zone including at least the first two hydration layers of the membrane. Possible origins of the preferential exclusion are discussed. As a direct consequence of the pronounced preferential exclusion, DMSO generates an osmotic stress at the membrane interface. This tends to stabilize lipid phases of low surface areas and to withdraw water from multilamellar stacks of membranes. Based on this, we suggest that the preferential exclusion of DMSO explains both the modulation of phase behavior and the constriction of multilamellar aggregates induced by this solute.

Glycine betaine as a cryoprotectant for prokaryotes

Osmoprotectants are low molecular weight, hydrophilic, nontoxic molecules that assist a cell under osmotic stress to stabilize its concentration of internal solutes. These properties are similar to compounds used as cryoprotectants for the preservation of prokaryotic cells during freezing. This study tested the ability of a common compatible solute, glycine betaine (GB), to act as a cryoprotectant. In a series of freeze-drying studies using a variety of prokaryotes, GB performed as well, or better than, two commonly used cryoprotectants, sucrose/bovine serum albumin (S/BSA) and trehalose/dextran (T/D). GB did especially well maintaining cell viability after long-term storage (simulated equivalent of 20 years) for microorganisms like Neisseria gonorrhoeae and Streptococcus pneumoniae. GB was tested for its ability to preserve members of the genus Acidothiobacillus, a difficult genus to preserve. For two strains of Acidithiobacillus ferrooxidans that were preserved using liquid drying, GB performed as well as S/BSA. Results were more mixed for two strains of Acidithiobacillus thiooxidans; one strain could be preserved with S/BSA but not GB, the other strain gave low recoveries with both cryoprotectants. GB also proved to be a useful cryoprotectant for liquid nitrogen preservation yielding equivalent results to the cryopreservative, glycerol for halophilic archaea, and neutrophilic Fe-oxidizing bacteria. These results indicate that GB is a simple and useful cryoprotectant that works for a wide range of prokaryotic organisms under different cryopreservation regimens.

Thermal properties of ethylene glycol aqueous solutions

Preventing ice crystallization by transforming liquids into an amorphous state, vitrification can be considered as the most suitable technique allowing complex tissues, and organs cryopreservation. This process requires the use of rapid cooling rates in the presence of cryoprotective solutions highly concentrated in antifreeze compounds, such as polyalcohols. Many of them have already been intensively studied. Their glass forming tendency and the stability of their amorphous state would make vitrification a reality if their biological toxicity did not reduce their usable concentrations often below the concentrations necessary to vitrify organs under achievable thermal conditions. Fortunately, it has been shown that mixtures of cryoprotectants tend to reduce the global toxicity of cryoprotective solutions and various efficient combinations have been proposed containing ethanediol. This work reports on the thermal properties of aqueous solutions with 40, 43, 45, 48, and 50% (w/w) of this compound measured by differential scanning calorimetry. The glass forming tendency and the stability of the amorphous state are evaluated as a function of concentration. They are given by the critical cooling rates v(ccr)above which ice crystallization is avoided, and the critical warming rates v(cwr) necessary to prevent ice crystallization in the supercooled liquid state during rewarming. Those critical rates are calculated using the same semi-empirical model as previously. This work shows a strong decrease of averaged critical cooling and warming rates when ethanediol concentration increases, V(ccr) and V(cwr) = 1.08 x 10 (10) K/min for 40% (w/w) whereas V(ccr) = 11 and V(cwr) = 853 K/min for 50% (w/w). Those results are compared with the corresponding properties of other dialcohols obtained by the same method. Ethylene glycol efficiency is between those of 1,2-propanediol and 1,3-propanediol.

Cell size and water permeability as determining factors for cell viability after freezing at different cooling rates

This work studied the viabilities of five types of cells (two yeast cells, Saccharomyces cerevisiae CBS 1171 and Candida utilis; two bacterial strains, Escherichia coli and Lactobacillus plantarum; and one human leukemia K562 cell) as a function of cooling rate during freezing. The range of investigated cooling rates extended from 5 to 30,000 degrees C/min. Cell viability was classified into three ranges: (i) high viability for low cooling rates (5 to 180 degrees C/min), which allow cell water outflow to occur completely and do not allow any intracellular crystallization; (ii) low viability for rapid cooling rates (180 to 5,000 degrees C/min), which allow the heat flow to prevail over water outflow (in this case, cell water crystallization would occur as water was flowing out of the cell); (iii) high viability for very high cooling rates (>5,000 degrees C/min), which allow the heat flow to be very rapid and induce intracellular crystallization and/or vitrification before any water outflow from the cell. Finally, an assumption relating cell death to the cell water crystallization as water is flowing out of the cell is made. In addition, this general cell behavior is different for each type of cell and seems to be moderated by the cell size, the water permeability properties, and the presence of a cell wall.