Change in pyrimidine deoxyribonucleoside metabolism in cell culture caused by Mycoplasma (PPLO) contamination

Mycoplasma hyorhinis induces proinflammatory responses in mice lymphocytes

Mycoplasmas are frequent contaminants of cultured cells, leading to alterations in cellular gene expression, protein synthesis, signal transduction, and metabolic pathways. Mycoplasma hyorhinis, the major contaminant of tissue cultures, has been implicated in a variety of diseases in swine. Most human and animal mycoplasmas remain attached to the surface of epithelial cells. Nonetheless, we have recently shown that M. hyorhinis is able to invade nonphagocytic melanoma cells. In the present study, we show by confocal laser scanning microscopy, that by exposing mice splenocytes to intact M. hyorhinis, intracellular mycoplasmas were detected. Mycoplasmal components were not detected within splenocytes after exposure to heat inactivated M. hyorhinis or to a purified M. hyorhinis lipoprotein (LPP) fraction. However, incubation of the splenocytes with intact M. hyorhinis cells, heat inactivated cells or M. hyorhinis LPP fraction induced accelerated cell proliferation and the secretion of interferon gamma and interleukin 17. Thus, M. hyorhinis and its LPPs can be added to the list of infectious agents causing direct stimulation of proinflammatory responses by mammalian lymphocytes.

Presence of the arginine dihydrolase pathway in Mycoplasma

Barile, Michael F. (Division of Biologics Standards, National Institutes of Health, Bethesda, Md.), Robert T. Schimke, and Donald B. Riggs. Presence of the arginine dihydrolase pathway in Mycoplasma. J. Bacteriol. 91:189-192. 1966.-The presence of the arginine dihydrolase pathway was examined in 61 Mycoplasma strains representing at least 18 Mycoplasma species isolated from nine different sources: human, bovine, avian, murine, swine, goat, canine, sewage, and tissue cell culture origin. Some species were represented by only one or two strains. Different strains of the same species gave the same results. Ten species (56%) were positive. Many nonpathogenic Mycoplasma species (M. hominis, type 1 and 2, M. fermentans, M. salivarium, and M. gallinarum) were positive, whereas most pathogenic species (M. pneumoniae, M. gallisepticum, M. neurolyticum, and M. hyorhinis) were negative. The presence of arginine dihydrolase activity among Mycoplasma species may prove to be useful for purposes of identification and classification.

[Mycoplasma as a contaminant of cell cultures maintained in laboratories of private and official institutions]

Mycoplasma is one of the most serious contaminants of cell cultures. Its detection is very important in virology, as well as its eradication. The aim of this study was to verify the incidence of mycoplasma in cell lines maintained in seven laboratories of private, government and college institutions of the State of São Paulo, Brazil, for the purposes of research, production of reagents for diagnosis and production of biologicals for human and animal use. Of the 29 cell lines, eight were derived from human tissues and 21 from other animal species (dog, rabbit, mouse, hamster, monkey, pig, chicken and ox). Using the direct method with specific liquid and solid media for detection of mycoplasma, 48 out of the 106 cell samples tested were positive, corresponding to a contamination index of 45.28%. The incidence of contamination among the 35 cell samples of human origin was 51.43% (18 positive). Of the 71 samples originated from other species, 30 were positive (42.25%). The high incidence of contamination found calls for the adoption of measures for the prevention of this hazard: the elimination of mouth pipetting, the use of aseptic techniques and a rigid control of trypsin, serum and other components of cell culture media. The substitution of mycoplasma-free cultures for all contaminated ones and the performance of periodical tests for mycoplasma detection must also be carried out to prevent and avoid the dissemination of these organisms. Data obtained showed that contamination appeared in the 2nd (72.92%), in the 3rd (20.83%) and in the 4th passage (6.25%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Deoxycytidine on Mycoplasma-Associated Inhibition of Thymidine Incorporation and Growth in Antifolate-Containing Media

Several mycoplasma species markedly inhibit lymphokine- and mitogen-induced3H-thymidine incorporation in cultured lymphoid cells, but have negligible short-term effects on cellular DNA synthesis as assessed by cytofluorography or by cell counts. The deoxyribonucleotide precursor deoxycytidine (dC) reverses this inhibition, but has little effect on isotope incorporation in uninfected cultures. Human lymphoblastoid leukemia cell lines contaminated with mycoplasma and hypoxanthine guanosine phosphoribosyl transferase (HGPRT)-deficient subclones do not grow in conventional HAT medium, but the unselected parent lines proliferate when dC is included in the culture medium. The beneficial effect of dC on the growth of contaminated cultures in selection medium is amplified by the addition of the cytidine deaminase inhibitor tetrahydrouridine (THU). These observations and corroborating nucleotide pool analysis suggest that dC may exert its beneficial effects on cellular proliferation and isotope utilization by inhibiting a mycoplasma-associated enzyme, thymidine phosphorylase. The data also suggest that the conversion of dC to dU by the cellular enzyme cytidine deaminase reduces the ability of dC to salvage contaminated cultures in the presence of an antifolate. The addition of dC to the culture medium in various3H-thymidine incorporation assays makes possible the detection of stimulatory lymphokines despite the presence of mycoplasma contamination of the indicator cells. The normalization of nucleotide pools and cellular growth of mycoplasma-infected HGPRT (+) human leukemic cell lines with the addition of dC to HAT selection medium has made possible the use of infected HGPRT-deficient subclones as fusion partners in the generation of T-T hybridomas. Our studies also suggest that the ability of cells to grow in HAT medium only when dC is included is presumptive evidence for mycoplasma infection.

Problems and pitfalls in assessing human T-lymphocyte mutant frequencies

The measurement of 6-thioguanine-resistant frequencies in human T-lymphocytes has been used to quantitate the in vivo HPRT mutant frequency. The data so far indicate a large variability in normal healthy individuals. The reliability with which wells are identified for clonal growth in the assay was investigated using 5 different methods of scoring: visual scoring, uptake of [3H]thymidine (either by cut off point or by statistical analysis), cell count and cytogenetic analysis. None of these methods presented a viable means of scoring the assay. An examination of the statistical precision of the assay under the limitations imposed by the experimental conditions leads to the conclusion that there is a large inherent error associated with the estimated mutant frequencies. Analysis of the T-lymphocyte subpopulations by cell surface monoclonal antibodies also leads us to believe that the observed mutant frequencies may not be representative of the true in vivo mutant frequencies. If the assay is to be used as a sensitive screen for individual or population exposure to possible mutagens, a closer understanding of the biology of the assay is indicated, and a comprehensive reevaluation of the methodology required. The utility of the system for studying qualitative aspects of human mutagenesis is not in doubt.

Inhibition of [3H]thymidine incorporation by Mycoplasma arginini-infected cells due to enzymatic cleavage of the nucleoside

Culture supernatants contaminated by Mycoplasma arginini inhibit the incorporation of [3H]thymidine ([3H]dThd) by cytotoxic T lymphocyte cell lines. This study presents evidence that the inhibition of uptake of the nucleoside is due to the rapid cleavage of the exogenous [3H]dThd into thymine. Uridine and cytidine as well as dThd are degraded by the mycoplasma-contaminated supernatants, while no cleavage was observed with uninfected supernatants. Cells contaminated by mycoplasma apparently release a pyrimidine-specific nucleosidase, possibly a dThd phosphorylase, which is responsible for the inhibition.

A sensitive and quantitative microassay for the detection of mycoplasma contamination: inhibition of IL-2 dependent cell line proliferation

A simple, rapid and sensitive microassay for mycoplasma detection in cell culture is reported. The assay is based on the fact that culture supernatants from contaminated cells inhibit [3H]thymidine incorporation by an IL-2 dependent mouse cytotoxic T cell line (CTLL). The mechanism of inhibition is related to the production by several mycoplasma strains of a pyrimidine-specific nucleoside phosphorylase which can degrade the radiolabelled thymidine used for the measurement of DNA synthesis. These strains were the commonest contaminants in cultures of 24 cell lines from 5 different sources. To establish the sensitivity of the test to detect mycoplasmas we have also used the inhibition assay to monitor the clearance of mycoplasma from 2 contaminated cell lines.

Mycoplasma contamination: a hazard of screening hybridoma supernatants for inhibition of [3H]thymidine incorporation

We have utilized a functional screen, inhibition of proliferation of mitogen activated lymphocytes, in an attempt to obtain monoclonal antibodies to soluble mediators of immune responses and to the receptors for such mediators. We have found that contamination of hybridoma cell lines with certain species of mycoplasma can interfere with such a screen. By consuming thymidine, mycoplasma can either mimic the effect of antibodies that inhibit lymphocyte proliferation or obscure the presence of antibodies that stimulate or enhance proliferation.

Uridine phosphorylase from Acholeplasma laidlawii: purification and kinetic properties

Uridine phosphorylase was purified 1,370-fold from sonicated extracts of Acholeplasma laidlawii by ammonium sulfate precipitation, DEAE-Sephadex column chromatography, hydroxylapatite chromatography, and Sephadex G-200 fractionation. The molecular weight of the enzyme as determined by gel filtration was approximately 65,000. [U-14C]ribose-1-phosphate (Rib-1-P), prepared enzymatically from [U-14C]inosine, was utilized in initial velocity studies of uridine synthesis, which indicated a sequential reaction with a KmUra of 110 microM and a KmRib-1-P of 17 microM. The kinetics of uridine cleavage were assessed at a saturating cosubstrate concentration, resulting in a KmUrd of 170 microM and a KmPi of 120 microM. These results indicate that an intracellular flux from uracil to uridine is kinetically feasible. However, such flux would be metabolically unproductive, since the low affinity of uridine kinase (KmUrd = 3.2 mM) precludes the operation of uridine phosphorylase and uridine kinase in tandem to convert uracil to UMP. We conclude that uridine phosphorylase performs only a catabolic function in A. laidlawii.

Treatment of cultured human colon carcinoma cells with fluorinated pyrimidines

The shape of the initial part of the dose-dependent response curve of LoVo cells, an established human colon carcinoma cell line, exposed for 1 hr to graded concentrations of 5-FU depended on the medium supplement, i.e., fetal calf serum (FCS), in which the cells were treated and subsequently incubated for colony-formation. At concentrations of 50--100 micrograms/ml (equivalent to peak plasma levels following an in vivo bolus dose of 15 mg/kg) cell kill was completely prevented by FCS. The serum did not contain thymidine (TdR) but had significant amounts of uridine (UR). When 5-FU was delivered in dialyzed FCS, concentrations of 50--100 micrograms/ml achieved only a modest 15% cell kill after 1 hour treatment. Regardless of medium supplement, the killing effect of 5-FU did not increase beyond concentrations greater than 2,000 micrograms/ml. Increasing the exposure interval dramatically increased the killing of LoVo cells by 5-FU, although the effects of medium supplement on the degree of cell survival persisted for about 12 hours. Virtually all of the incorporated 5-FU was transformed into 5-FUR, and a very small proportion eventually was incorporated into nucleic acids, suggesting that the killing effect of 5-FU on LoVo cells is mediated mostly by ribosidation and not by conversion into the deoxyribonucleoside. This conclusion is supported by the failure of 5-FUdR to kill LoVo cells after a treatment interval of one hour, even at concentrations of 5000 micrograms/ml; yet after the same exposure interval, 5-FUR effectively killed cells at concentrations of 50--100 micrograms/ml. TdR afforded no protection from cell kill by 5-FU. In contrast, UR was capable of protecting LoVo cells from the lethal effects of both 5-FU and 5-FUR even at concentrations as low as 10 micrograms/ml. Ftorafur exposed to LoVo cells for 1 hour had a slight killing effect (about 20--25%) at concentrations ranging up to 2000 micrograms/ml. Although the lethal effect of ftorafur was slightly increased after longer periods of incubation, it failed to reach 90% even after intervals of 48 hours. The results on cellular sensitivity that we obtained for LoVo cells treated with various fluorinated pyrimidines differ substantially from those of other investigators who used different methods to assess cell killing on nonhuman and noncolonic cell systems. The predictive relevance of these data as compared to those obtained in other systems is justified by the suboptimal results with these agents in clinical practice.

Some radiobiological consequences of mycoplasma contamination of mammalian cells in tissue culture

Cells of the mouse Ehrlich ascites carcinoma grown in vitro became contaminated with an arginine-splitting mycoplasma. The slopes of the radiation dose-survival curves of the contaminated cells, assayed by colony-forming ability, were extremely variable; eventually it became impossible to grow colonies at all. Experiments on the feeder cell requirement showed that, whereas for clean cells the maximum plating efficiency was obtained within a range of 5 X 10(4) and 4 X 10(5) feeder cells in a 5 cm dish, contaminated cells would only produce colonies in the presence of between 10(4) and 3 X 10(4) feeder cells. Doubling the concentration of arginine in the medium allowed contaminated cells to grow with maximum plating efficiency within an increased range of 10(4) and 4 X 10(5) feeder cells. The mycoplasmas were apparently behaving as feeders, reducing the requirement for added feeder cells, but also depleting the medium of essential arginine. The cells were eventually decontaminated by passing them through a mouse as an ascites tumour.

Differences in incorporation of nucleic acid bases and nucleosides by various Mycoplasma and Acholeplasma species

Eight species representative of the serological diversity of the Mycoplasmatales were tested for their ability to incorporate radiolabeled nucleic acid precursors into acid-insoluble material. Cultures in complex growth medium were centrifuged and resuspended in minimal essential medium (Eagle). For Acholeplasma laidlawii, labeling occurred mainly during the first 4 h of incubation, with substrate saturation at 20 micron. All organisms tested incorporated uracil, adenine, and guanine; none incorporated cytosine. Thymine was incorporated only by bovine group 7, Mycoplasma putrefaciens, and Mycoplasma pneumoniae (strain 3546), but deoxynucleosides enhanced thymine incorporation in A. laidlawii, Mycoplasma gallisepticum, M. pneumoniae (strain AP-164), and Mycoplasma hyorhinis. Nucleoside incorporation (adenosine, guanosine, uridine, cytidine, and thymidine) was not observed for the arginine-utilizing species, Mycoplasma hominis and Mycoplasma arginini, whereas all other organisms tested incorporated nucleosides. The incorporation pattern provides additional metabolic evidence to support the biochemical and antigenic diversity of these organisms. The recognition of differences in incorporation of nucleic acid precursors is important not only to the specific labeling of these organisms, but also to the study of metabolism and transport.

Adenosine phosphorylase activity in a mutant HEp-2 cell line contaminated with Mycoplasm hyorhinis

Metabolic studies in HEp-2/MP,MIR cells (an adenosine kinase, hypoxanthine phosphoribosyltransferase negative mutant) indicated the presence of adenosine phosphorylase activity. This activity, unknown in established mammalian cell lines, resulted in the glycosidic cleavage of both adenosine and the antiviral drug arabinosyladenine. The activity was observed readily in the presence or absence of the adenosine deaminase inhibitor conformycin. Isopycnic separation of [3H] thymidine-labeled DNA species in CsCl density gradients resulted in the appearance of two distinct peaks. The heavier peak coincided with [14C]thymidine-labeled marker DNA of human origin, whereas the lighter peak was within the range associated with mycoplasmal DNA. Testing by commercial laboratories confirmed the presence of mycoplasma in HEp-2/MP,MIR cells. The contaminant was identified as Mycoplasma hyorhinis, a porcine mycoplasma. Following gamma-irradiation (3000 rads) to block cellular mitosis, the mucoplasma-contaminated HEp-2/MP,MIR cells were cocultivated with mycoplasma-free wild-type HEp-2 cells which did not exhibit adenosine phosphorylase activity. Following serial cocultivation in a medium designed to favor the survival of the wild-type cells, adenosine phosphorylase activity was found in the previously uninfected cells. Studies of this nature emphasize the need for investigators to carefully monitor their cell lines for mycoplasma.

Adenosine phosphyorylase activity as distinct from inosine-guanosine phosphorylase activity in Sarcoma 180 cells and rat liver

Adenosine phosphorylase (EC 2.4.2.-) activity present in Sarcoma 180 cells grown in culture and in rat liver, is shown to be distinct from inosine-guanosine phosphorylase by several criteria: (a) treatment of Sarcoma 180 cell extract with p-chloromercuribenzoate inhibited the two activities to a different extent, (b) adenine selectively protected the adenosine phosphorylase activity of Sarcoma 180 and rat liver extract against heat inactivation, while hypoxanthine selectively protected inosine-guanosine phosphorylase activity, (c) at nearly saturating substrate concentrations and using Sarcoma 180 extract, the rates of ribosylation of a mixture of adenine + hypoxanthine or adenine + guanine, but not of hypoxanthine + guanine, were found to be almost equal to the sum of their individual rates as measured separately, (d) inosine selectively inhibited the ribosylation of hypoxanthine and guanine catalysed by Sarcoma 180 and rat liver extract while 2-chloroadenosine selectively inhibited the ribosylation of adenine and N6-furfuryladenine, (e) pH vs. activity curves were similar with hypoxanthine or guanine as the substrate but they were markedly different from the curve with adenine as the substrate. The potential role of adenosine phosphorylase activity in vivo is discussed.

Differences in the incorporation of bromodeoxyuridine by human lymphoblastoid cell lines

Long term human lymphoblastoid lines differ in their ability to grow in medium containing bromodeoxyuridine (BrdU) and to incorporate analog into their DNA. Eight Burkitt's lymphoma cell lines divided at least twice in BrdU-containing medium and made DNA in which over 90% of the thymidine residues were substituted with analog in both strands. Three infectious mononucleosis-derived lines and 24 lines transformed in vitro were inhibited by BrdU after one cell division and made only hybrid DNA in which one strand was substituted with analog. One out of eight normal individuals from whom long term lines were prepared gave cell lines which divided at least twice in BrdU and gave DNA in which both strands were substituted with analog. It would appear that intrinsic cellular factors regulate the response to BrdU and that Burkitt's tumor lines are characterized by their ability to make stable doubly substituted DNA containing a high proportion of halogenated analog.

Comparison of methods for the detection of Mycoplasmal contamination of cell cultures: a review

Several reviews in recent years have emphasized the problems created by mycoplasmal contamination of cultured cells (1-5). Because of the hazards of interpreting data derived from mycoplasma contaminated cells, most cell biologists routinely screen their cultures for the presence of these organisms. In recent years, the limitations of standard microbiological testing for mycoplasmas have become increasingly apparent and have led to the development of several new biochemical techniques for detection of these organisms. The aim of this review is to describe and compare available detection techniques and to evaluate their relative efficacy. Those properties of mycoplasmas that are relevant to their role as cell culture contaminants will be briefly discussed.

Mycoplasmas and cell cultures

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Taxonomic comparison of the amino termini of microbial cell proteins

A comparison was made of the distribution of amino terminal end groups in the cellular proteins of a number of microbes. Among the procaryotes, methionine is a highly variable but virtually ubiquitous major protein end group. This is consistent with its possible role as a general amino acid initiator of protein biosynthesis in the procaryotes. Generally, however, alanine is the most abundant of the major end groups, followed in decreasing order by serine, threonine, the acidic amino acids, and occasionally lysine. No other new major end-groups were found. Among 15 representatives of the Enterobacteriaceae, retention of the initiating methionine terminus of the cellular protein varies considerably at a tribal level and is randomized at a familial level. The profiles of the five remaining end groups, however, are strikingly uniform, and are, for example, close to but significantly different from those of the Erwineae. Among the taxonomically more heterogeneous Bacillaceae, end-group profiles vary more and are sometimes unrelated. End-group analysis is thus particularly useful as a molecular criterion of taxonomy in assessing familial homogeneity. Free NH(2) termini in eucaryote cell proteins are fewer, and they have increased acidic amino acid components and no methionine; they are otherwise similar to those of the procaryotes.

Mycoplasmal deoxyribonuclease activity in virus-infected L-cell cultures

Cell-free extracts of Mycoplasma hominis and medium from 72-hr broth cultures had deoxyribonuclease activity like that of deoxyribonuclease I. Mg(++) stimulated activity, and the pH optimum was between 8.0 and 9.0. Double-stranded or heatdenatured deoxyribonucleic acid (DNA) served as a substrate, and oligonucleotides were produced. Cell-free extracts of L cells infected with M. hominis or M. hominis plus equine abortion virus (equine herpes virus, EAV) had greatly increased activity over that of extracts of L cells or of L cells infected with EAV alone. In the absence of M. hominis, however, extracts had little activity, most of which was in virus-infected cell cultures. Activity was found in the culture medium only in those systems in which M. hominis was present. It is concluded that M. hominis can contribute significant deoxyribonuclease activity to virus-infected as well as virusfree cell cultures. Perhaps the most interesting question arising concerns the ability of EAV, a DNA virus, to replicate successfully despite the presence of deoxyribonuclease activity at the site of replication (the nucleus).

New assay procedure for separation of mycoplasmas from virus pools and tissue culture systems

Presence of mycoplasma organisms in tissue culture systems and virus pools was detected by titration of the contaminated material on agarose-suspended BHK21/13S cells. The use of this method permitted isolation of mycoplasmas which could not be detected by standard assay methods. Mycoplasma colonies at concentrations ranging from 10(4) to 10(6) colony-forming units/ml in agarose-BHK21/13S media could be distinguished from virus plaques, and the two populations of microorganisms could be easily disassociated either by electron microscopy or by biological methods. All isolated mycoplasmas were identified in growth inhibition tests as belonging to the GDL group. The growth inhibition test on agarose-BHK21/13S cell suspension plates could also be applied directly to those strains which could not be isolated by standard assay procedures.

Compraison of mycoplasmas associated with human tumors, leukemia, and tissue cultures

Leach, R. H. (Wellcome Research Laboratories, Beckenham, Kent, England), and M. Butler. Comparison of mycoplasmas associated with human tumors, leukemia, and tissue cultures. J. Bacteriol. 91:934-941. 1966.-Mycoplasmas originally isolated by various workers from tissue cultures prepared from or inoculated with tumor or leukemic cells fell into four groups; each related to existing species or serotypes. These were Mycoplasma pulmonis, M. fermentans, M. hominis, and the GDL serotype, the last two being well known as contaminants of uninoculated cell lines. All the test strains were able to grow well in certain tissue cultures, and some caused cytopathic effects and acidity. These observations are discussed in terms of the relationship of these strains to the malignant tissues with which they were originally associated. The variable results obtained in certain biological tests on these strains emphasized the need for standardization of the conditions under which such tests may be employed to assist in identification of Mycoplasma species.

ULTRASTRUCTURE OF A MYCOPLASMA (NEGRONI) ISOLATED FROM HUMAN LEUKEMIA

Hummeler, Klaus (The Children's Hospital of Philadelphia, Philadelphia, Pa.), Natale Tomassini, and Leonard Hayflick. Ultrastructure of a mycoplasma (Negroni) isolated from human leukemia. J. Bacteriol. 90:517-523. 1965.-A strain of mycoplasma isolated in tissue cultures from human leukemic bone marrow was cultivated in cell-free media for 23 passages. Concentrates of broth cultures were investigated under the electron microscope in thin sections and negative contrast. The ultrastructure of the mature mycoplasma cells and their elementary bodies is described. It was found that the elementary bodies, particularly in the negative contrast preparations, bear a close resemblance to viruslike particles seen in tissues and plasmas of leukemic patients.