Computer Simulation of Clostridium botulinum Strain 56A Behavior at Low Spore Concentrations

It is generally assumed that spore behavior is independent of spore concentration, but recently published mathematical models indicate that this is not the case. A Monte Carlo simulation was employed in this study to further examine the independence assumption by evaluating the inherent variance in spore germination data. All simulations were carried out with @Risk software. A total of 500 to 4,000 iterations were needed for each simulation to reach convergence. Lag time and doubling time from a higher inoculum concentration were used to simulate the time to detection (TTD) at a lower inoculum concentration under otherwise identical environmental conditions. The point summaries of the simulated and observed TTDs were recorded for the 26 simulations, with kinetic data at the target inoculum concentration. The ratios of the median (R_m = median_obs/median_sim) and 90% range (R_r = 90% range_obs/90% range_sim) were calculated. Most R_m and R_r values were greater than one, indicating that the simulated TTDs were smaller and more homogeneous than the observed ones. R_r values departed farther from one than R_m values. Ratios obtained when simulating 1 spore with 10,000 spores deviated the farthest from one. Neither ratio was significantly different from the other when simulating 1 spore with 100 spores or simulating 100 spores with 10,000 spores. When kinetic data were not available, the percent positive observed at the 95th percentile of the simulated TTDs was obtained. These simulation results confirmed that the assumption of independence between spores is not valid.     

A Quantitative Dynamic Simulation of Bremia lactucae Airborne Conidia Concentration above a Lettuce Canopy

Lettuce downy mildew, caused by the oomycete Bremia lactucae Regel, is a major threat to lettuce production worldwide. Lettuce downy mildew is a polycyclic disease driven by airborne spores. A weather-based dynamic simulation model for B. lactucae airborne spores was developed to simulate the aerobiological characteristics of the pathogen. The model was built using the STELLA platform by following the system dynamics methodology. The model was developed using published equations describing disease subprocesses (e.g., sporulation) and assembled knowledge of the interactions among pathogen, host, and weather. The model was evaluated with four years of independent data by comparing model simulations with observations of hourly and daily airborne spore concentrations. The results show an accurate simulation of the trend and shape of B. lactucae temporal dynamics of airborne spore concentration. The model simulated hourly and daily peaks in airborne spore concentrations. More than 95% of the simulation runs, the daily-simulated airborne conidia concentration was 0 when airborne conidia were not observed. Also, the relationship between the simulated and the observed airborne spores was linear. In more than 94% of the simulation runs, the proportion of the linear variation in the hourly-observed values explained by the variation in the hourly-simulated values was greater than 0.7 in all years except one. Most of the errors came from the deviation from the 1:1 line, and the proportion of errors due to the model bias was low. This model is the only dynamic model developed to mimic the dynamics of airborne inoculum and represents an initial step towards improved lettuce downy mildew understanding, forecasting and management.     

Bacillus megaterium spore germination is influenced by inoculum size

AIMS: The effect of spore density on the germination (time-to-germination, percent germination) of Bacillus megaterium spores on tryptic soy agar was determined using direct microscopic observation. METHODS AND RESULTS: Inoculum size varied from approximately 10(3) to 10(8) cfu ml(-1) in a medium where pH=7 and the sodium chloride concentration was 0.5% w/v. Inoculum size was measured by global inoculum size (the concentration of spores on a microscope slide) and local inoculum size (the number of spores observed in a given microscope field of observation). Both global and local inoculum sizes had a significant effect on time-to-germination (TTG), but only the global inoculum size influenced the percentage germination of the observed spores. CONCLUSIONS: These results show that higher concentrations of Bacillus megaterium spores encourage more rapid germination and more spores to germinate, indicating that low spore populations do not behave similarly to high spore populations. SIGNIFICANCE AND IMPACT OF THE STUDY: A likely explanation for the inoculum size-dependency of germination would be chemical signalling or quorum sensing between Bacillus spores.     

Solid-state production of polygalacturonase by Aspergillus sojae ATCC 20235

The effect of solid substrates, inoculum and incubation time were studied using response surface methodology (RSM) for the production of polygalacturonase enzyme and spores in solid-state fermentation using Aspergillus sojae ATCC 20235. Two-stage optimization procedure was applied using D-optimal and face-centered central composite design (CCD). Crushed maize was chosen as the solid substrate, for maximum polygalacturonase enzyme activity based on D-optimal design. Inoculum and incubation time were determined to have significant effect on enzyme activity and total spore (p<0.01) based on the results of CCD. A second order polynomial regression model was fitted and was found adequate for individual responses. All two models provided an adequate R(2) of 0.9963 (polygalacturonase) and 0.9806 (spores) (p<0.001). The individual optimum values of inoculum and incubation time for maximum production of the two responses were 2 x 10(7) total spores and 5-6 days. The predicted enzyme activity (30.55 U/g solid) and spore count (2.23 x 10(7)spore/ml) were very close to the actual values obtained experimentally (29.093 U/g solid and 2.31 x 10(7)spore/ml, respectively). The overall optimum region considering the two responses together, overlayed with the individual optima. Solid-state fermentation provided 48% more polygalacturonase activity compared to submerged fermentation under individually optimized conditions.     

Dispersal of Septoria nodorum Pycnidiospores by Simulated Rain and Wind

The influence of wind on the splash dispersal of Septoria nodorum pycnidiospores was studied in a raintower/wind tunnel complex with single drops or simulated rain falling on spore suspensions or infected stubble with windspeeds of 1.5 to 4 m/sec. When single drops fell on spore suspensions (depth 0.5 mm, concentration 7.8 × 10⁵ spores/ml) most of the spore-carrying droplets collected on fixed photographic film between 0–4 m downwind (windspeed 3 m/sec) were >200 μm in diameter. However, most spores were carried in droplets with diameter > 1000 μm, 70 % of which carried more than 100 spores. When simulated rain fell on infected stubble most of the spore-carrying droplets collected beyond 1 m downwind (windspeeds 1.4 and 4 m/sec) were <200 μm in diameter and none were >600 μm; most of these droplets carried only one spore. The distribution of splash droplets (with diameter >100 μm) deposited on chromatography paper showed a maximum at 40–50 cm upwind of the target but many more droplets were deposited 20–30 cm downwind, when single drops fell on a spore suspension (concentration 1.2 × 10⁵ spores/ ml) containing fluorescein dye with a windspeed of 2 m/sec; droplets were collected up to 3 m downwind but not more than 70 cm upwind. With a windspeed of 3 m/sec, numbers of sporecarrying droplets and spores collected on film decreased with increasing distance downwind; most were collected within 2 m of the target but some were found up to 4 m. When simulated rain fell on infected stubble, increasing the windspeed from 1.5 to 4 m/sec greatly increased the number of spores deposited more than 1 m downwind. At 1.5 m/sec none were collected beyond 2 m downwind, whereas at 4 m/sec some were collected at 4 m. A few air-borne S. nodorum spores were collected by suction samplers at a height of 40 cm at distances up to 10 m downwind of a target spore suspension on which simulated rain fell.     

Production of pectolytic enzymes by Aspergillus niger: effect of inoculum size and potassium hexacyanoferrate II-trihydrate

Summary The effect of inoculum size and potassium hexacyanoferrate II-trihydrate, K₄[Fe(CN)₆]·3 H₂O (KHCF), on pectinase synthesis by Aspergillus niger in submerged conditions were studied. Experiments were performed in shake flasks and in a 10-1 stirred bioreactor. Spore concentrations in the range 10²–10⁸ spores/1 of substrate were tested. Enzyme activity measured by the Apple Juice Depectinizing Assay (AJDA) showed the highest values using the smallest inoculum. Higher spore concentrations led to a 25% or even up to a 50% reduction of activity. Polygalacturonase (PG) activity decreased similarly to AJDA activity with higher inoculum concentration. Pectinlyase (PL) showed the opposite relationship, while pectin esterase (PE) did not show any correlation with inoculum concentration. Experiments in the fermentor using a reduced inoculum of 10² spores/1 showed that the whole process was prolonged in comparison to 10⁸ spores/1 inoculum. A pronounced effect of KHCF on fungal morphology as well as on enzymatic activity was observed. With increased concentration the morphology gradually changed from loose pellets to smaller compact ones. The enzymatic activity was markedly improved. In the bioreactor the amount of biomass was reduced from about g/l to 8 g/l. The activities were improved in comparison to fermentations without KHCF as follows: AJDA from 68 to 112 units (U)/ml, viscosity reduction from 83% to 90%, PG from 0.8 to 3.3 U/ml, PE from 32 to 49 U/ml and PL from 0.05 to 0.12 U/ml. The fermentation time was reduced from 96 to 68 h. Offprint requests to: J. Friedrich     

Media and Fermentation Processes for the Rapid Production of High Concentrations of Stable Blastospores of the Bioinsecticidal Fungus Paecilomyces fumosoroseus

In shake flask and fermentor studies, various media components and culture inocula were tested to improve P. fumosoroseus spore production rates, yield and stability. To evaluate inoculum potential and inoculum scale-up for fermentor studies, conidia and liquid culture-produced spores of various strains of P. fumosoroseus were compared as inoculum. Inoculation of liquid cultures with blastospores at concentrations of at least 1×10⁶ spores mL^-1 resulted in the rapid production of high concentrations of blastospores (∼1×10⁹ spores mL^-1, 48 h fermentation time) for all strains tested. The rapid germination rate of blastospores (90% after 6 h incubation) compared to conidia (>90% after 16 h incubation) and the use of higher inoculum rates reduced the fermentation time from 96 to 48 h for maximal spore yields. A comparison of various complex nitrogen sources showed that liquid media supplemented with acid hydrolyzed casein or yeast extract supported the production of high concentrations of blastospores that were significantly more desiccation-tolerant (79-82% survival after drying) when compared to blastospores produced in media supplemented with other nitrogen sources (12-50% survival after drying). For rapid spore production, requirements for trace metals and vitamin supplementation were dependent on the type of hydrolyzed casein used in the medium. Fermentor studies with two strains of P. fumosoroseus showed that high concentrations (1.3-1.8×10⁹ spores mL^-1) of desiccation-tolerant blastospores could be produced in 48-h fermentations. These studies have demonstrated that the infective spores of various strains of the fungal bioinsecticide Paecilomyces fumosoroseus can be rapidly produced using deep-tank, liquid culture fermentation techniques.     

False-negative rate and recovery efficiency performance of a validated sponge wipe sampling method

Recovery of spores from environmental surfaces varies due to sampling and analysis methods, spore size and characteristics, surface materials, and environmental conditions. Tests were performed to evaluate a new, validated sponge wipe method using Bacillus atrophaeus spores. Testing evaluated the effects of spore concentration and surface material on recovery efficiency (RE), false-negative rate (FNR), limit of detection (LOD), and their uncertainties. Ceramic tile and stainless steel had the highest mean RE values (48.9 and 48.1%, respectively). Faux leather, vinyl tile, and painted wood had mean RE values of 30.3, 25.6, and 25.5, respectively, while plastic had the lowest mean RE (9.8%). Results show roughly linear dependences of RE and FNR on surface roughness, with smoother surfaces resulting in higher mean REs and lower FNRs. REs were not influenced by the low spore concentrations tested (3.10 × 10(-3) to 1.86 CFU/cm(2)). Stainless steel had the lowest mean FNR (0.123), and plastic had the highest mean FNR (0.479). The LOD(90) (≥1 CFU detected 90% of the time) varied with surface material, from 0.015 CFU/cm(2) on stainless steel up to 0.039 on plastic. It may be possible to improve sampling results by considering surface roughness in selecting sampling locations and interpreting spore recovery data. Further, FNR values (calculated as a function of concentration and surface material) can be used presampling to calculate the numbers of samples for statistical sampling plans with desired performance and postsampling to calculate the confidence in characterization and clearance decisions.     

Effects of inoculum level and pressure pulse on the inactivation of Clostridium sporogenes spores by pressure-assisted thermal processing

The effects of initial concentration and pulsed pressurization on the inactivation of Clostridium sporogenes spores suspended in deionized water were determined during thermal processing (TP; 105 degrees C, 0.1 MPa) and pressure-assisted thermal processing (PATP; 105 degrees C and 700 MPa) treatments for 40 min and 5 min holding times, respectively. Different inoculum levels (10(4), 10(6), and 10(8) CFU/ml) of C. sporogenes spores suspended in deionized water were treated at 105 degrees C under 700 MPa with single, double, and triple pulses. Thermally treated samples served as control. No statistical significances (p > 0.05) were observed among all different inoculum levels during the thermal treatment, whereas the inactivation rates (k1 and k2) were decreased with increasing the initial concentrations of C. sporogenes spores during the PATP treatments. Double- and triple-pulsed pressurization reduced more effectively the number of C. sporogenes spores than single-pulse pressurization. The study shows that the spore clumps formed during the PATP may lead to an increase in pressure-thermal resistance, and multiple-pulsed pressurization can be more effective in inactivating bacterial spores. The results provide an interesting insight on the spore inactivation mechanisms with regard to inoculum level and pulsed pressurization.     

Spore Yield and Microcycle Conidiation of Colletotrichum gloeosporioides in Liquid Culture

The effect of V8 juice concentration (5 to 40%, vol/vol), spore inoculum density (10⁵ and 10⁷ spores per ml), and liquid batch or fed-batch culture condition on mycelium and spore production by Colletotrichum gloeosporioides was evaluated. The amount of mycelium produced, the time required for initiation of sporulation following attainment of maximum mycelium, and the time for attainment of maximum spore concentration increased with increasing V8 juice concentration in batch culture. Cultures containing V8 juice at >10% achieved a similar spore density (apparent spore-carrying capacity) of about 0.8 mg of spores per ml (1 × 10⁷ to 2 × 10⁷ spores per ml) independent of inoculum density and V8 juice concentration. The relative spore yield decreased from a high of 64% of the total biomass for the low-inoculum 5% V8 culture, through 13% for the analogous 40% V8 culture, to a low of 2% for the high-inoculum 27% V8 culture. Fed-batch cultures were used to establish conditions of high spore density and low substrate availability but high substrate flux. The rate of addition of V8 juice was adjusted to approximate the rate of substrate utilization by the (increasing) biomass. The final spore concentration was about four times higher (3.0 mg of spores per ml) than the apparent spore-carrying capacity in batch culture. This high spore yield was obtained at the expense of greatly reduced mycelium, resulting in a high relative spore yield (62% of the total biomass). Microcycle conidiation occurred in the fed-batch but not batch systems. These data indicate that substrate-limited, fed-batch culture can be used to increase the amount and efficiency of spore production by C. gloeosporioides by maintaining microcycle conidiation conditions favoring allocation of nutrients to spore rather than mycelium production.     

Microcycle Conidiation and Spore-Carrying Capacity of Colletotrichum gloeosporioides on Solid Media

The effect of spore inoculum density, medium concentration, and temperature on slime-spot formation, spore yield, and mycelium production by Colletotrichum gloeosporioides on agar media were studied with a simple microplate assay. A steady-state spore yield (spore-carrying capacity) independent of inoculum density was reached only on media that supported good fungal growth and sporulation. The spore-carrying capacity was reached earlier, the denser the inoculum. On standard mycological media a high inoculum density (2.5 × 10⁶ spores per ml) resulted in a slimy mass of conidia forming a slime spot, a phenomenon associated with greatly reduced mycelium formation and indicative of microcycle conidiation. In contrast, for a similar inoculum density, enhanced mycelial growth preceded sporulation and overrode slime-spot formation on highly concentrated media; a very low medium concentration resulted in much less mycelium, but spore production was also decreased. Exposure to suboptimal growth temperatures of 36 to 48°C for up to 8 days did not induce microcycle conidiation from inocula that did not form a slime spot at 28°C.     

Size distribution in some Middle Devonian dispersed spores and its bearing on the problem of the evolution of heterospory

Some Middle Devonian dispersed spore species have been studied whose size range embraces the arbitrary demarcation line of 200 μm in diameter generally accepted for the identification of a megaspore. The spore size distribution for one species is unimodal while those for other three species are bimodal. The spores of the smaller size classes (the presumed microspores) are relatively large, the means being 90 μm, 100 μm and 207 μm. The morphological features of the spores imply their progymnospermous affinity. It is suggested that in progymnosperms, in the course of heterospory evolution, the increase in spore size occurred before size differentiation and, presumably, before sex determination. The cause of the size increase might have been endospory, which may thus have occurred previous to the last two events.     

Detection and quantification of airborne conidia of Fusarium circinatum, the causal agent of pine pitch canker, from two California sites by using a real-time PCR approach combined with a simple spore trapping method

Pinus radiata (Monterey pine), a tree native to coastal California and Mexico, is widely planted worldwide for timber production. A major threat to Monterey pine plantations is the fungal disease pine pitch canker, caused by Fusarium circinatum (Hypocreales). We present a novel trapping approach using filter paper in combination with a rapid molecular method to detect the presence of inoculum in the air. The assay is also useful for diagnosing the presence of the pathogen on plants. The test is based on the F. circinatum specific primer pair CIRC1A-CIRC4A, which amplifies a 360-bp DNA fragment in the intergenic spacer region of the nuclear ribosomal operon. Real-time PCR was used to calculate the number of fungal spores present in each reaction mixture by comparing the threshold cycle (Ct) of unknown spore samples to the Ct values of standards with known amounts of F. circinatum spores. The filter paper method allows prolonged and more sensitive spore sampling in the field compared to traditional traps using petri dishes filled with selective medium. A field test at two sites in coastal California infested with pine pitch canker was carried out during the summer and fall of 2002. Spore counts were in the range of ca. 1 x 10(3) to ca. 7 x 10(5)/m(2), with the highest spore counts in the fall, suggesting a seasonal fluctuation.     

Dosage effect study of the microsporidian Octosporea muscaedomesticae in the adult black blowfly Phormia regina,with reference to the reproductive cycle of the pathogen

The quantitative pathogenicity of the microsporidian Octosporea muscaedomesticae in adult Phormia regina was studied. Dosage levels ranging from 10² to 10⁶ spores per fly were administered to five and six groups of newly emerged, starved adult flies in two trials. Rates of mortality and infection were determined. A direct relationship between number of spores ingested and subsequent infection rate was found in a 4-day trial while no such relationship was found in an 18-day trial, using the same source of inoculum and host flies from the same colony. The lack of a direct relationship between spore dose and rate of infection in the 18-day trial is explained on the basis of the short spore-to-spore development time of the parasite. New generations of spores formed within the host tissues obscure the results in relation to the spore dose initially administered. An appreciable number of spores in the inoculum is needed to initiate frank infection. The ID₅₀ (median infective dose) was 4.4 × 10⁴ spores per fly after 4 days.     

Effect of Sodium Chloride and pH on the Outgrowth of Spores of Type E Clostridium botulinum at Optimal and Suboptimal Temperatures

The sodium chloride inhibition of spore outgrowth of four strains of type E Clostridium bolulinum was determined in a Trypticase-peptone-glucose (TPG) medium. At 16, 21, and 30 C, spores of three strains required 5.0% and one strain 4.5% salt for complete inhibition during 1 year of incubation. At 8 and 10 C, spores of the four strains required 4.5% salt for definite inhibition. Salt concentrations slightly lower than those providing inhibition tended to extend spore outgrowth time at low temperatures. The minimal pH permitting outgrowth of type E spore inocula was affected by the concentration of reducing compound present in the system. When either 0.02% sodium thioglycolate or 0.05% L-cysteine hydrochloride was used, outgrowth at 30 and 8 C occurred at much lower pH levels than when 0.2% thioglycolate was added. At 30 C, spores of one strain showed outgrowth in TPG medium as low as pH 5.21 with an inoculum of 2 million spores per replicate tube. At a 10-fold higher inoculum, the same strain showed outgrowth at pH 5.03 in one of five replicate tubes. At 8 C, spore outgrowth of the four strains occurred at pH 5.9, but not at pH 5.7, in TPG medium containing L-cysteine hydrochloride.     

Coating Beauveria bassiana with lignin for protection from solar radiation and effects on pathogenicity to Lygus lineolaris (Heteroptera: Miridae)

The entomopathogenic fungus, Beauveria bassiana, is highly susceptible to the damaging effects of solar radiation. This study demonstrates protection from simulated solar radiation by coating B. bassiana (GHA) spores with lignin and effects on pathogenicity to Lygus lineolaris (Palisot de Beauvois) adults in direct spray and contact uptake bioassays. Spores were coated with either lignin or cross-linked lignin by spray drying to produce spore coatings of high and low water solubility, respectively. Non-coated spores and the two spore coating treatments were suspended in either water (0.04% Silwet L77) or oil (Orchex 692) to produce six formulations. Rates of loss in spore viability under simulated solar radiation were approximately ten times lower for the three formulations in which spores remained coated in suspension (cross-linked lignin in water, cross-linked lignin in oil, and lignin in oil). However, these three formulations were the least pathogenic. Estimates of LC₅₀ and LC₇₅ values for the most pathogenic formulation (non-coated in oil) were 5 and 12 times lower, respectively, than the least pathogenic formulation (cross-linked lignin in oil), but these differences were not significant. The three lignin-coated formulations that provided the greatest UV protection were also the least pathogenic based on LT values, which were significant. Overall, L. lineolaris mortality was approximately 80 times less when exposed to treated broccoli rather than sprayed directly, based on LC₅₀ values. If the contribution of spore uptake from plant surfaces to L. lineolaris mortality is similarly low under field conditions, then improving persistence may be less important for improving efficacy. However, under control conditions where solar radiation significantly impacts mycoinsecticide efficacy, the improved persistence of lignin coating formulations may outweigh negative effects on pathogenicity.     

Use of sucrose-agar globule with root exudates for mass production of vesicular arbuscular mycorrhizal fungi

A sucrose-agar globule (SAG) was newly introduced to increase production of the vesicular arbuscular mycorrhizal (VAM) fungal spores, Gigaspora gigantea and Glomus fasciculatum. An SAG inoculum and a sucrose-agar globule with root exudates (SAGE) inoculum were prepared, and their spore productions were compared with a soil inoculum. When the SAGE was used as the inoculum on sucrose-agar medium plates the number of spores was increased (35% more than the soil inoculum). After the soil inoculum and SAGE were inoculated on an experimental plant, Zingiber officinale, the percentage root colonization, number of VAM spores, and dry matter content were analyzed. It was observed that the SAGE showed a higher percentage of root colonization (about 10% more), and increases in the number of spores (about 26%) and dry matter (more than 13%) for the two VAM fungal spores than the soil inoculum. The results of this study suggested that the SAGE inoculum may be useful for the mass production of VAM fungi and also for the large scale production of VAM fungal fertilizer.     

Mass production of spores of lactic acid‐producing Rhizopus oryzae NBRC 5384 on agar plate

Mass production of sporangiospores (spores) of Rhizopus oryzae NBRC 5384 (identical to NRRL 395 and ATCC 9363) on potato‐dextrose‐agar medium was studied aiming at starting its L (+)‐lactic acid fermentation directly from spore inoculation. Various parameters including harvest time, sowed spore density, size of agar plate, height of air space, and incubation mode of plate (agar‐on‐bottom or agar‐on‐top) were studied. Ordinarily used shallow Petri dishes were found out to be unsuitable for the full growth of R. oryzae sporangiophores. In a very wide range of the sowed spore density, the smaller it was, the greater the number of the harvested spores was. It was also interesting to find out that R. oryzae grown downward vertically with a deep air space in an agar‐on‐top mode gave larger amount of spores than in an agar‐on‐bottom mode at 30°C for 7‐day cultivation. Scale‐up of the agar plate culture from 26.4 to 292 cm² was studied, resulting in the proportional relationship between the number of the harvested spores/plate and the plate area in the deep Petri dishes. The number of plates of 50 cm in diameter needed for 100 m³ industrial submerged fermentation started directly from 2 × 10⁵ spores/mL inoculum size was estimated as about 6, from which it was inferred that such a fermentation would be feasible. Designing a 50 cm plate and a method of spreading and collecting the spores were suggested. Bioprocess technological significance of the “full‐scale industrial submerged fermentation started directly from spore inoculation omitting pre‐culture” has been discussed. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:876–881, 2013     

Production of Clostridium bifermentans Spores as Inoculum for Bioremediation of Nitroaromatic Contaminants

Spores of Clostridium bifermentans KMR-1 were produced for use as a microbial inoculum for bioremediation and were preserved in both liquid and dry forms. All spore formulations showed good viability and ability to biodegrade the target compound, 2,4,6-trinitrotoluene (TNT), after 4 months of storage. For low-cost bulk spore production, several medium compositions, based on soy peptone, corn steep liquor, and meat peptone, were tested and yielded 10(sup7) spores per ml. A medium pH above 7.0, a low glucose concentration, and a sufficient concentration of protein favored the sporulation of C. bifermentans KMR-1.     

Analysis of the predicting variables for daily and weekly fluctuations of two airborne fungal spores: <Emphasis Type="Italic">Alternaria</Emphasis> and <Emphasis Type="Italic">Cladosporium</Emphasis>

Alternaria and Cladosporium are two fungal taxa whose spores (conidia) are included frequently in aerobiological studies of outdoor environments. Both spore types are present in the atmosphere of Malaga (Spain) throughout almost the entire year, although they reach their highest concentrations during spring and autumn. To establish predicting variables for daily and weekly fluctuations, Spearman's correlations and stepwise multiple regressions between spore concentrations (measured using a volumetric 7-day recorder) and meteorological variables were made with results obtained for both spore types in 1996 and 1997. Correlations and regressions were also made between the different taxa and their concentrations in different years. Significant and positive correlation coefficients were always obtained between spore concentrations of both taxa, followed by temperature, their concentrations in different years, sunshine hours and relative humidity (this last in a negative sense). For the two spore types we obtained higher correlation and regression coefficients using weekly data. We showed different regression models using weekly values. From the results and a practical point of view, it was concluded that weekly values of the atmospheric concentration of Alternaria spores can be predicted from the maximum temperature expected and its concentrations in the years sampled. As regards the atmospheric concentration of Cladoposrium spores, the weekly values can be predicted based on the concentration of Alternaria spores, thus saving the time and effort that would otherwise be employed in counting them by optical microscopy.