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PubMed2004

Comparison of the toxicity of reference mycotoxins and spore extracts of common indoor moulds.

There is an unclear endangering potential by toxic influences of inhaled conidiospores and therefore the conidia of indoor mould species were cultured and toxicologically examined after their mechanical disintegration. For this purpose high-performance liquid chromatography (HPLC) and three colorimetric bioassays, the PTGT (pollen tube growth test), the MB (methylene blue) and the MTT (methylthiazoltetrazolium) assay were applied. The sensitivity of the biological methods was evaluated by using 12 reference mycotoxins and 3 structural cell wall components. Only in one extract of disintegrated spores (Aspergillus fumigatus) a mycotoxin (0.22 microg gliotoxin/6.2 x 10(8) spores) was determined. All nine spore extracts, however, turned out to be cytotoxic and in this case the MTT assay was remarkably more sensitive than the two other test methods. The IC50 values of six different spore extracts determined by the MTT assay were lower than 10(6) spores/well (well = 0.2 ml) whereas the IC50 values determined by the MB assay and PTGT were higher than 10(6) spores per 0.2 ml for each spore extract. An examination of four spore extracts, which were fractionated depending on their polarity by HPLC, showed that single substances as well as synergistic effects contribute to the toxic properties of the spores. The results of this work indicate a health hazard due to toxic effects after the inhalation of extremely high spore concentrations of indoor moulds. This risk will also exist if the spores do not contain any mycotoxins.

Air Pollution, Indoor↗
PubMed2002

Spores of Aspergillus versicolor isolated from indoor air of a moisture-damaged building provoke acute inflammation in mouse lungs.

Microbial growth in moisture-damaged buildings has been associated with respiratory health effects, and the spores of the mycotoxin producing fungus Aspergillus versicolor are frequently present in the indoor air. To characterize the potential of these spores to cause harmful respiratory effects, mice were exposed via intratracheal instillation to a single dose of the spores of A. versicolor (1 x 10(5), 1 x 10(6), 5 x 10(6), 1 x 10(7), or 1 x 10(8) spores), isolated from the indoor air of a moisture-damaged building. Inflammation and toxicity in lungs were evaluated 24 h later by assessment of biochemical markers and histopathology. The time course of the effects was investigated with the dose of 5 x 10(6) spores for up to 28 days. The exposure to the spores increased transiently proinflammatory cytokine levels (tumor necrosis factor [TNF] alpha and interleukin [IL]-6) in bronchoalveolar lavage fluid (BALF). The cytokine responses were dose and time dependent. The highest cytokine concentrations were measured at 6 h after the dose, and they returned to the control level by 3 days. Moreover, the spores of A. versicolor recruited inflammatory cells into airways: Neutrophils peaked transiently at 24 h, macrophages at 3 days, and lymphocytes at 7 days after the dosing. The inflammatory cell response did not completely disappear during the subsequent 28 days, though no histopathological changes were seen at that time point. The spores did not induce expression of inducible nitric oxide synthase in lavaged cells. Only the highest spore dose (1 x 10(8)) markedly increased serum IL-6, increased vascular leakage, and caused cytotoxicity (i.e., increased levels of albumin, total protein, lactate dehydrogenase [LDH], and hemoglobin in BALF) in the airways. In summary, the spores of A. versicolor caused acute inflammation in mouse lungs. This indicates that they have potential to provoke adverse health effects in the occupants of moisture-damaged buildings.

Acute Disease↗
PubMed2006

Airborne fungal spores in a cross-sectional study of office buildings.

Airborne fungal spores were measured in 44 office buildings in the summer and winter throughout the continental United States, as part of the Building Assessment, Survey and Evaluation (BASE) program. Six indoor air and two outdoor air samples were collected on a single day from each building. The cross-sectional and repeated measure design afforded evaluation of between-building and within-building variability of fungal spore levels in buildings. Total fungal spore concentrations in indoor air ranged from < 24 to 1000 spores/m3, except for one building with natural ventilation where indoor levels were approximately 9000 spores/m3. Indoor air concentrations of total spores did not vary significantly between winter and summer or morning and afternoon monitoring periods or among climate zones or locations within a test area. Indoor-outdoor ratios of total spore concentrations typically ranged between 0.01 and 0.1 and were approximately seven times greater in winter than summer because of relatively low outdoor levels in the winter. The indoor-outdoor ratio of total spore concentrations for a building was consistent (reliability coefficient = 0.91) among repeated measures. Distributions of rank correlation coefficients for spore types in pairs of individual indoor-outdoor and indoor-indoor samples were weakly correlated (Spearman correlation = 0.2 on average). When spore type data were aggregated among samples from the same building, the central tendency of the rank correlation coefficients increased to 0.45. Rank correlation coefficients were also proportional to the number of spore types present in the samples that were compared. The BASE study provides normative data on concentrations of fungal spores that can aid in identification of problematic levels of mold in buildings.

Air Microbiology↗
PubMed1985

The microsporidian spore invasion tube. IV. Discharge activation begins with pH-triggered Ca2+ influx.

The microsporidian spore extrusion apparatus activates with a calcium influx from Spraguea lophii spore wall/plasma membrane; this influx requires preconditioning with an extrasporular shift in medium pH to the alkaline in the presence of the polyanions mucin or polyglutamate. Undischarged S. lophii spores display calcium bound to the wall/plasma membrane with a characteristic calcium-chlorotetracycline fluorescence; this fluorescence declines significantly during spore discharge. S. lophii spores do not discharge when spore wall/plasma membrane calcium is removed with EGTA. Extrasporular mucin or polyglutamate and a pH shift to the alkaline appear to be necessary preconditions for the triggering of the influx of spore wall/plasma membrane-bound 45Ca2+. Ionophore A-23187 also effectively activates spore discharge without other extrasporular polyanions. Micromolar concentrations of the calcium antagonists lanthanum or verapamil prevent spore discharge, and micromolar concentrations of calmodulin inhibitors chlorpromazine and trifluroperazine prevent spore discharge. Calmodulin, visualized with a calmodulin antibody and a peroxidase conjugate, is localized particularly on the plasma membrane and the polaroplast membranes of the extrusion apparatus.

Animals↗
PubMed1991

Gene activity during germination of spores of the fern, Onoclea sensibilis: RNA and protein synthesis and the role of stored mRNA.

Pattern of 3H-uridine incorporation into RNA of spores of Onoclea sensibilis imbibed in complete darkness (non-germinating conditions) and induced to germinate in red light was followed by oligo-dT cellulose chromatography, gel electrophoresis coupled with fluorography and autoradiography. In dark-imbibed spores, RNA synthesis was initiated about 24 h after sowing, with most of the label accumulating in the high mol. wt. poly(A) -RNA fraction. There was no incorporation of the label into poly(A) +RNA until 48 h after sowing. In contrast, photo-induced spores began to synthesize all fractions of RNA within 12 h after sowing and by 24 h, incorporation of 3H-uridine into RNA of irradiated spores was nearly 70-fold higher than that into dark-imbibed spores. Protein synthesis, as monitored by 3H-arginine incorporation into the acid-insoluble fraction and by autoradiography, was initiated in spores within 1-2 h after sowing under both conditions. Autoradiographic experiments also showed that onset of protein synthesis in the cytoplasm of the germinating spore is independent of the transport of newly synthesized nuclear RNA. One-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis of 35S-methionine-labelled proteins revealed a good correspondence between proteins synthesized in a cell-free translation system directed by poly(A) +RNA of dormant spores and those synthesized in vivo by dark-imbibed and photo-induced spores. These results indicate that stored mRNAs of O. sensibilis spores are functionally competent and provide templates for the synthesis of proteins during dark-imbibition and germination.

Autoradiography↗
PubMed2000

Synthesis and characterization of the spore proteins of Bacillus subtilis YdhD, YkuD, and YkvP, which carry a motif conserved among cell wall binding proteins.

We have previously reported that YaaH and YrbA are spore proteins of Bacillus subtilis that are required for spore resistance and/or germination and that they have a motif conserved among so-called cell wall binding proteins [Kodama et al. (1999) J. Bacteriol. 181, 4584-4591, Takamatsu et al. (1999) J. Bacteriol. 181, 4986-4994]. In this study, we analyzed the expression of ydhD, ykuD, and ykvP genes, which encode putative proteins containing the same motif. Transcription of ydhD was dependent on SigE, and the mRNA was detectable from 2 h after the cessation of logarithmic growth (T(2) of sporulation). ykuD was transcribed by SigK RNA polymerase from T(4) of sporulation. Both SigK and GerE were essential for ykvP expression, and this gene was transcribed from T(5) of sporulation. Inactivation of these genes by insertion of an erythromycin resistance gene did not affect vegetative growth, spore resistance to heat, chloroform, and lysozyme, or spore germination in the presence of L-alanine or in a mixture of L-asparagine, D-glucose, D-fructose, and potassium chloride. The His tag fusions of YdhD, YkuD, and YkvP downstream of their natural promoter regions were introduced into a multicopy plasmid. These fusion proteins were produced during sporulation in B. subtilis transformants and were detected in mature spores, indicating that YdhD, YkuD, and YkvP are all proteins intrinsic to spores. Excessive YkuD and YkvP in the sporulating cells did not affect spore resistance or germination. The cells producing excessive YdhD also did not show impaired spore resistance, but their germination properties were changed: the spores revealed reduced response to L-alanine and some of them germinated even without germinants. Escherichia coli b-lactamase, whose signal sequence had been genetically replaced by the cell wall binding motif of YaaH, was produced in sporulating cells, and Western blot analysis indicated that the fused protein was assembled into spores. We speculate that the conserved motif functions as a kind of signal sequence involved in assembly of these proteins on forespores.

Amino Acid Motifs↗
PubMed1984

The role of surface charge in ionic germination of Clostridium perfringens spores.

The surface charge against pH behaviour of spores of Clostridium perfringens type A was determined using a colloid titration method in the pH range 4-9. The native spores as well as various ionic forms of the spores loaded with divalent cations were found to be negatively charged. A positive colloid, MGCh, inhibited the ionic germination of the spores and this inhibition was highly dependent on pH. However, another positive colloid, GCh, did not inhibit the germination. Chemical modification of carboxyl groups on the spore surface by use of a water-soluble carbodiimide with two nucleophiles, glycine ethyl ester and taurine, caused spores not only to have little or no colloidal charge but also to lose the ability to germinate. The modification of carboxyl groups in the spore coat protein also resulted in elimination of, or marked reduction in its negative charge. These results suggest that carboxyl groups in the spore coat protein are the major negatively charged species on the spore surface. The role of surface charge in the ionic germination of the spores is discussed.

Amino Acids↗
PubMed2001

The role of antibodies to Bacillus anthracis and anthrax toxin components in inhibiting the early stages of infection by anthrax spores.

Vaccines which are efficacious against anthrax, such as the human vaccine, Anthrax Vaccine Absorbed (AVA), contain the protective antigen (PA) component of the anthrax toxins as the major protective immunogen. Although AVA protects against inhalational anthrax, the immune responses to and role in protection of PA and possibly other antigens have yet to be fully elucidated. Sera from animals immunized with a toxin-producing, unencapsulated live vaccine strain of Bacillus anthracis have been reported to have anti-spore activities associated with the antitoxin humoral response. The authors performed studies to determine whether anti-PA antibody (Ab)-containing preparations stimulated spore uptake by phagocytes and suppressed the germination of spores in vitro. AVA- and PA-immune sera from several species enhanced the phagocytosis by murine peritoneal macrophages of spores of the virulent Ames and the Sterne vaccine strains. Antitoxin Abs appeared to contribute significantly, although not solely, to the enhanced uptake. Rabbit antisera to PA purified from either Sterne or a PA-producing pX01-cured recombinant, affinity-purified anti-PA IgG, and monkey antisera to AVA were used to assess the role of anti-PA ABS: Rabbit anti-PA Abs promoted the uptake of spores of the PA-producing strains Sterne, Ames and RP42, a mutant of Sterne producing only PA, but not of the pX01-Sterne-1 strain, Ames strain, or RP4, a mutant of Sterne with deletions in the loci encoding PA and the oedema factor (EF) toxin component and producing only the lethal factor toxin component. Rabbit anti-PA and monkey anti-AVA Abs also significantly inhibited spore germination in vitro compared to preimmune serum or medium. Spore-associated proteins recognized by anti-PA Abs were detected by electron microscopy and confirmed by immunoblotting of spore coat extracts. Thus, the anti-PA Ab-specific immunity induced by AVA has anti-spore activity and might have a role in impeding the early stages of infection with B. anthracis spores.

Animals↗
PubMed2002

Killing of spores of Bacillus subtilis by peroxynitrite appears to be caused by membrane damage.

During an infection of a higher eukaryote, dormant spores of a Bacillus species have been previously shown to be present in cells that can generate the toxic agent peroxynitrite (PON). Dormant spores of Bacillus subtilis were much more resistant to killing by PON than were growing cells, and spore-coat alteration or removal greatly decreased PON resistance. Spores were not killed by PON through DNA damage and lost no dipicolinic acid (DPA) during PON treatment. However, PON-killed spores lost DPA during subsequent heat treatments that caused much less DPA release from untreated spores. Although dead, the PON-killed spores germinated and initiated metabolism but never went through outgrowth; the great majority of germinated PON-killed spores also took up propidium iodide, indicating that they had suffered significant membrane damage and were dead. Together these data suggest that spore killing by PON is through some type of damage to the spore's inner membrane.

Bacillus subtilis↗
PubMed1989

Recovery of spores of Clostridium difficile altered by heat or alkali.

The effect of heating or alkali-treatment on spore recovery in ordinary growth medium was examined for four strains of Clostridium difficile. Heating spores at 80 degrees C for 10 min produced 95.50-99.95% decreases in the recovery rates. Treatment with 0.1 N NaOH for 15 min produced 99.47 and 99.83% decreases in spore recovery rates for two of the four strains. The influence of either addition of lysozyme after treatment with sodium thioglycollate (thioglycollate-lysozyme method) or addition of sodium taurocholate (taurocholate method) on recovery of heat- or alkali-treated C. difficile spores was also examined. Viable spores of all strains altered by heating at 90 degrees C or 100 degrees C for 10 min could not be recovered at all by the taurocholate method. Nor did this method allow recovery of alkali-altered spores treated with greater than 0.2 N NaOH for 15 min. On the other hand, 10-47% of altered spores heated at 90 degrees C for 10 min were recovered by the thioglycollate-lysozyme method, and alkali-altered spores treated with 0.1-0.3 N NaOH for 15 min were as completely recovered by this method as untreated spores. These results indicate that the thioglycollate-lysozyme method is more effective than the taurocholate method for recovery of the heat- or alkali-altered C. difficile spores.

Clostridium↗
PubMed1994

Monoclonal antibodies for Streptomyces lividans and their use for immunomagnetic capture of spores from soil.

Monoclonal antibodies were produced to Streptomyces lividans spore surface antigens. One particular hybridoma cell line, 43H6, produced a monoclonal antibody that reacted exclusively with Streptomyces cluster group 21 in an enzyme-linked immunosorbent assay (ELISA). Antibody 43H6 was found to be of subclass IgG1, kappa light chain. Western blot (immunoblot) analysis revealed that 43H6 recognized a major outer spore polypeptide of about 37,000 Da. The epitope was stably maintained in S. lividans spores over at least seven sporulation cycles on laboratory medium and for at least 14 weeks in sterile soil systems. The species group specificity of antibody 43H6 was exploited in the development of an immunocapture technique for the isolation of streptomycetes from soil. Magnetic beads coated with antibody 43H6 were mixed with soil samples seeded with S. lividans spores. Spore-bead complexes were recovered using magnets. Treatment of beads with blocking agents and the inclusion of detergents in the recovery system lessened non-specific binding of spores to beads and improved recovery. In buffer solutions decreasing the spore concentration increased the recovery values for a fixed bead concentration. At a spore concentration of 5 x 10(7) ml-1 the recovery was 4.3% whilst at 5 x 10(2) ml-1 it was 76% for a fixed bead concentration of 0.6 mg ml-1. Using a bead concentration of 2 mg per 10 g soil, approximately 30% of the target spore population of 10(6) c.f.u. was recovered from sterile soil and 4% from non-sterile soil. This method offers a rapid means of selectively recovering and concentrating Streptomyces spores from soil samples.

Antibodies, Bacterial↗
PubMed1992

Disruption of the sporulation-specific gene spiA in Dictyostelium discoideum leads to spore instability.

The spiA gene of Dictyostelium is expressed specifically in prespore cells and spores during culmination, the final stage of development during which prespore and prestalk cells undergo terminal differentiation to form spores and stalk. We have used homologous recombination to delete this gene and have characterized the resulting phenotype. The spiA- strains develop normally and produce spores that are indistinguishable from those of wild-type strains by transmission and scanning electron microscopy. Mutant spores have normal viability when assayed soon after the completion of development, but, as the spiA- spores age, they lose viability more rapidly than those of the spiA+ parent. The drop in viability is more pronounced when spores are submerged in dilute buffer at a concentration that does not allow germination; after 11 days submerged, the viability of spiA- spores is 10(5)-fold reduced, whereas that of the parent is decreased only 10-fold. Reinserting an intact copy of the spiA gene into a spiA- strain restores the stability of its spores. The product of the spiA gene, Dd31, was identified on Western blots as a 30-kD protein using an antibody raised against a fusion protein containing a portion of the coding sequence. Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner. This location is consistent with its observed role in maintaining stability of the spores.

Animals↗
PubMed1985

Germination of the decoated spores of Bacillus megaterium.

Decoated spores of Bacillus megaterium ATCC 12872 were prepared by extracting the inner coat components with an alkaline solution containing sodium dodecyl sulfate and dithiothreitol (SDS-DTT) from outer coat-deficient mutant spores, which were produced from one of the mutants isolated and named MAE-05 by us. The decoated mutant spores germinated as well as the intact spores of the mutant and the parent, indicating that the outer and inner spore cats cannot be essential structures for the initiation of germination. When the SDS-DTT-treated MAE-05 spores were converted to H-spores by incubation in citrate-phosphate buffer (pH 3.5) at 30 C for 3 hr, they lost their germinability by glucose and KNO3. Ca-spores, prepared by treating H-spores with 10 mM calcium acetate at 37 C for 60 min, regained the germinability. Experiments on the interaction of 45Ca with the cortex and the inner membrane isolated from H-spores suggested that the calcium present in the inner membrane might be related to germinability.

Bacillus megaterium↗
PubMed1983

Mechanism of chemical manipulation of the heat resistance of Clostridium perfringens spores.

The mechanism of chemical manipulation of the heat resistance of Clostridium perfringens type A spores was studied. Spores were converted to various ionic forms to base-exchange technique and these spores were heated at 95 degrees C. Of the four ionic forms, i.e. Ca2+, Na+, H+ and native, only hydrogen spores appeared to have been rapidly inactivated at this temperature, when survivors were enumerated on the ordinary plating medium. However, the recovery of the survivors was improved when the plating medium was supplemented with lysozyme, and more dramatically when the heated spores were pretreated with alkali followed by plating in the medium containing lysozyme. In contrast to crucial damage to germination, in particular to spore lytic enzyme, no appreciable amount of DPA was released from the heat-damaged H-spores. These results suggest that a germination system is involved in the thermal inactivation of the ionic forms of spores, and that exchangeable cation load plays a role in protection from thermal damage of the germination system within the spore. An enhancement of thermal stability of spore lytic enzyme in the presence of a high concentration of NaCl was consistent with the hypothesis.

Calcium↗
PubMed2005

Relationship between physiochemical properties, aggregation and u.v. inactivation of isolated indigenous spores in water.

AIMS: The objective of the study was to compare ultraviolet (u.v.) inactivation kinetics of indigenous aerobic spores in surface water with their laboratory-cultured spore isolates and to investigate the relationship between physicochemical characteristics and u.v. inactivation kinetics of spore isolates. METHODS AND RESULTS: Lake water samples were analysed for the presence of indigenous aerobic spores. Different bacterial isolates from the heterogeneous indigenous population were genetically characterized, resporulated and examined for hydrophobicity, surface charge, particle size distribution and survival at different u.v. 254 nm fluence levels. Cultured isolated spores exhibited a three-stage inactivation curve consisting of shoulder, first order and tailing regions whereas indigenous spores exhibited only one stage of linear kinetics. Hydrophobicity of the Bacillus spore isolates was inversely related to the extent of u.v. inactivation before tailing occurred. CONCLUSIONS: Tailing in the u.v. inactivation curves results from aggregation of a portion of the spore population because of hydrophobic interactions, supporting the link between aggregation of spores, hydrophobicity and u.v. inactivation. SIGNIFICANCE AND IMPACT OF THE STUDY: Evidence of the link between spore physicochemical parameters and u.v. disinfection performance furthers the understanding of factors that affect inactivation of microbes in natural waters supplied to drinking water treatment plants.

Bacillus↗
PubMed2006

Synthesis of alpha-glucans in fission yeast spores is carried out by three alpha-glucan synthase paralogues, Mok12p, Mok13p and Mok14p.

Fission yeast possesses a family of (1,3)-alpha-glucan synthase-related genes; one of them, mok1+/ags1+, plays an essential function in morphogenesis during vegetative growth. Here we show that three mok1+ paralogues -mok12+, mok13+ and mok14+- are required for sporulation to succeed, acting at different stages of the spore wall maturation process. Mutation of mok12+ affected the efficiency of spore formation and spore viability. Deletion of mok13+ does not affect spore viability but the spores showed reduced resistance to stress conditions. mok14Delta mutant spores failed to accumulate the amylose-like spore wall-specific polymer. mok12+, mok13+ and mok14+ expression was restricted to sporulating cells and the proteins localized to the spore envelope but with different timing. mok11+ was also induced during the sporulation process although its deletion did not show apparently a sporulation defect. In vegetative cells, beta-glucans are more abundant than alpha-glucans (55% versus 28%). In spores, the situation was the opposite, alpha-glucans accounted for 46% while beta-glucans were approximately 38% of the total polysaccharides. We found at least two types of alpha-glucan polymers, Mok12p and Mok13p, were involved in the synthesis of the greater part of alpha-glucan in the spores envelope, a polymer that is mainly digested with alpha-1,3 glucanase, while Mok14p, homologous to starch synthases, was required for the synthesis of the iodine-reactive polymer that is made of alpha-1,4 glucose residues.

Amylose↗
PubMed2004

Assessment of the aerosolization potential for fungal spores in moldy homes.

UNLABELLED: The airborne fungal concentration measured with air samplers during specific time intervals may not adequately represent the indoor air quality because of the sporadic nature of spore release from sources. The conventional source evaluation (e.g. swab and tape sampling) characterizes the mold source but does not relate to the fraction of spores that can be aerosolized from a contaminated material. As an alternative to these methods, we have recently developed and laboratory-tested a novel Fungal Spore Source Strength Tester (FSSST). It allows assessing the potential of aerosolization of fungal spores from contaminated surfaces under the most favorable release conditions. In this study, the FSSST was used to characterize the release of spores from four building materials in mold-problem homes. The spores of different species were efficiently aerosolized by the FSSST, exhibiting a total spore release rate ranging approximately from 10(2) to 10(3) cm2/min. For all tested materials, <2% of the spores on the contaminated surface were released during the tests. The airborne spore concentration estimated from the release rate data was found in most cases to be significantly greater than the concentration actually measured in these environments with simultaneous air sampling. The results suggest that the FSSST can be used for the assessment of maximum potential exposure to airborne spores released from identified sources in homes. PRACTICAL IMPLICATIONS: A recently developed FSSST was found to be suitable to measure the aerosolization potential of indoor fungal sources at the most favorable release conditions. The FSSST generates the data that allows assessing the strength of mold sources in homes with respect to their maximum ability to contaminate indoor air with fungi. The novel approach bridges two conventional methods, the air sampling and the direct source evaluation (e.g. swab sampling), thus providing a better representation of the airborne fungal exposure than these methods individually. The device prototype can be used for evaluating the effectiveness of environmental interventions by taking samples before and after the intervention. As a broader application, the FSSST can be utilized for assessing the release of various hazardous biological and non-biological particles from contaminated surfaces.

Air Microbiology↗
PubMed1981

Physiological effects of ultraviolet light on Dictyostelium discoideum spore germination.

The spore germination in Dictyostelium discoideum consists of four stages: activation, postactivation lag, swelling and emergence. Ultraviolet irradiation (total fluence of 250 J/m(2)) of spores at any time prior to late spore swelling allows full swelling, but inhibits the emergence of myxamoebae. In the case of freshly activated spores, a UV exposure time of 30 s (total fluence of 50 J/m(2)) is sufficient to reduce emergence to about 6% when measured after 24 h of incubation. This same fluence results in about 10% viability as measured by plaque forming ability. Experiments utilizing "fractionated exposures' result in the same percentage inhibition of emergence as that found for "single exposures' provided the total fluence is equivalent. The higher fluences (250 J/m(2)) which completely prevent emergence, do not affect the endogenous oxygen uptake of spores during swelling. Ultraviolet light irradiated spores respond to the same activation and deactivation treatments as control unirradiated spores. Ultraviolet irradiation after late spore swelling allows emergence to occur in only a small fraction of the population. This fraction of cells which can emerge after UV treatment is said to have passed a "competence point', which is believed to be the time when all the events necessary for emergence have been completed. Though the sites of UV inactivation in spores can only be postulated at present, it is apparent that the initial stages of germination (activation, postactivation lag and spore swelling) occur independently of the UV sensitive sites. The final stage of germination (emergence), however, is dependent on UV sensitive functions.

Dictyostelium↗