Bruce Lighthart

Survey of Culturable Airborne Bacteria at Four Diverse Locations in Oregon: Urban, Rural, Forest, and Coastal

A bstractTo determine the risks of microbial air pollution from microorganisms used for pesticides and bioremediation, or emanating from composting, fermentation tanks, or other agricultural and urban sources, airborne microbial levels must be evaluated. This study surveyed the atmospheric load of culturable bacteria at four locations in Oregon: a city street, a rye grass field, a Douglas fir forest, and a bluff on the Pacific coast. Samples (20–60 min each) were taken using slit and six-stage cascade samplers. Samples were taken over two 10- or 24-h periods, depending on the site. Meteorological measurements were made at each location.The quantity and type of bacteria found varied by location and time. The highest average number of bacteria during daylight hours was exhibited at the urban site (609 cfu/m3), followed by the forest site (522 cfu/m3), then the rural site (242 cfu/m3), with the lowest concentration found at the coastal site (103 cfu/m3). During the 24-h sampling periods at the rural site, bacterial concentration, in general, tended to increase at sunrise, decrease during the solar noon hours, gradually increase until sunset, then decrease into the evening, with the lowest concentrations occurring between 2100 and 0500 hours. Pigmented bacteria represented between 21 and 62% of the total bacteria sampled; the highest percentage of pigmented bacteria was found at the rural site, and the lowest percentage at the forest site. Bacillus was found to be the most abundant single genus represented at all locations (12–45%). The majority of bacteria found were associated with particles greater than 3 μm aerodynamic diameter. Information gathered from this survey combined with data from the literature and future surveys will contribute to the detection and description of microbial air pollution.

The effects of microbial pesticides on non-target, beneficial arthropods

Abstract The formulation, testing protocol, lethal effects, sub-lethal effects, ecological relationships and selectivity of microbial pesticides on non-target, beneficial arthropod natural enemies of insect and mite pests are reviewed for viruses, bacteria, fungi and protozoa. In general, it was found that: (1) effects from indirect mortality of natural enemies are probably more significant across all microbial types than are direct mortalities from microbial pesticides; (2) significant levels of direct mortality of beneficial insects can be caused by bacterial and protozoan microbial pesticides; (3) no direct mortality from viruses of pests has been documented for arthropod natural enemies; (4) the direct effect of fungi on arthropod natural enemies has not been well studied and probably has been underestimated; (5) unique standard methods need to be developed for microbial assays and for expressing more exactly the dosage administered to the host or natural enemy.

The Annual Bacterial Particle Concentration and Size Distribution in the Ambient Atmosphere in a Rural Area of the Willamette Valley, Oregon

Airborne bacterial samples were collected using wet cyclone and cascade impact samplers 2 to 3 times a week at 2 agricultural sites in the mid-Willamette River valley, near Corvallis, OR during 1997. The concentrations of total (TB), culturable (CB), and particulate-associated culturable (PACB) bacteria in the ambient atmosphere were measured using epifluorescence microscopic and culture methods. All three categories of airborne bacteria were found to have major concentration peaks in the summer (e.g., from June to September), especially in July and August. This may reflect the greater summer flux of bacteria from agricultural sources and activities and dry/dusty soil conditions. The PACB had several smaller peaks scattered in the winter and autumn. Size analysis of the PACB showed that the summer PACB peak was composed primarily of larger bacterial particles, whereas the smaller peaks in other seasons were composed primarily of smaller bacterial particles that occur during rainfall or storms events. The concentrations of TB and CB were positively correlated with temperature and solar radiation, but negatively with relative humidity. This is thought to reflect the contributions of agricultural activities and solar ground-heating effects outweighing the biologically damaging/lethal effects of solar radiation, high temperature, and dry conditions. It was shown that the count median diameter (CMD) of the PACB varied during the year with no obvious seasonal pattern. The ratios of CB to PACB and CB to TB concentrations in the atmosphere were greater in the summer than in the other seasons, while the TB to PACB ratio was the greatest in the spring. These observations could be interpreted as follows: more culturable bacteria, compared with the total, were aggregated in clumps or rafted on plant/soil debris in the summer, while single or relatively fewer culturable bacteria were associated with the particles in other seasons. This may be caused by the newly exposed bacterial particles with a high proportion of culturable bacteria, short transport time interval from aerosolization to deposition in the sampler, and/or more resistant bacterial populations in/on the summer-time sources. Spring airborne bacterial populations may be more sensitive to, and/or extensively exposed to, environmental stresses (starvation, sunlight, etc.) and aerosolization, thus fewer culturable bacteria per particle might be expected. A seasonal microstructure illustration of airborne bacteria particles is proposed that may be useful for the interpretation of aerobiological data, the investigation of health or ecological effect, and the detection of the 3 categories of airborne bacteria defined herein.

Mini-review of the concentration variations found inthe alfresco atmospheric bacterial populations

Variations in the atmospheric surface layers culturable, and to a lesser extent, total bacteria-associated atmospheric particlecharacteristics will be discussed in terms of (a)their temporal variation from 2 min resolutionthrough diurnal to annual periods, (b) the effect ofmeteorological conditions on their abundance andsize, (c) total to culturable bacterial ratio, and(d) the total number of bacteria per culturableparticle (e) bacterial survival in droplet/particles, and (f) the general particle size distribution including aerodynamic Count MedianDiameter (CMD).Meteorological and topographic conditions thatcontrol total and culturable bacteria-associatedatmospheric particle concentration will be presentedin terms of (a) precipitation, (b) wind direction,(c) time of day, (d) sky conditions (i.e., cloudy,sunny, rain, etc.), (e) season, and (f) atmosphericinversion conditions.Simulation models will be described that supporthypotheses of diurnal and annual concentrationcycles in the Earths (and perhaps other planetaryatmospheres) atmospheric surface layer.

Bacterial flux from chaparral into the atmosphere in mid-summer at a high desert location

Abstract Estimates of the bacterial flux for a daylight cycle were observed at the Hanford Nuclear Reservation, Richland, WA, during June 1992, using a modified Bowen ratio method. The upward daytime bacterial flux was coupled with the solar radiation/sensible heat cycle, but commenced 2 h later in the morning and ceased 3 h earlier in the afternoon. During this period, the maximum flux was ca . 17,000 Colony Forming Units (CFU) m- 2 h −1 occurring at solar noon, resulting in a total upward bacterial flux of ca . 76,000 CFU m −2 for the time period. During this same period, the integrated total viable bacterial concentration in the atmosphere was only 0.81 % of total upward bacterial flux. The high temperatures (e.g. 45 C), low relative humidity (e.g. 10%), and particularly high solar radiation (e.g. 910 W m −2 ) are thought to be the lethal agents in the high desert atmosphere. The decreasing concentration of bacteria in the atmosphere was found to slow within 30 min of the initiation of the upward flux of bacteria. Even though the upward flux of bacteria decreased after solar noon, the bacterial concentration in the atmosphere continued to increase. Presumably, this is due to reduced solar radiation in the afternoon allowing greater survival of the released bacteria and smaller dilution of entering bacteria into the shallow nocturnal mixed layer.

Solar radiation has a lethal effect on natural populations of culturable outdoor atmospheric bacteria

Abstract Ambient heterogenic atmospheric bacteria were collected by impaction directly onto nutrient agar surfaces on clear sunny and cloudy days and at night. Samples were then exposed to summer noontime solar radiation (SR) for increasing periods of time. Bacterial survival was the least for the organisms collected at nighttime and the greatest for those collected during clear sunny days. This result may be due to the inactivation of SR-sensitive bacterial populations by the ambient SR on clear days, and to a lesser extent on cloudy days, leaving only the relatively resistant populations. This does not occur at night when the SR-sensitive populations have not been reduced. The mixed bacterial species populations in the atmosphere do not appear to follow the Bunsen-Roscoe reciprocity law but integration of pure bacterial components of the mixed population that do follow the law, could explain the findings. The populations collected in this investigation exhibited SR survival functions usable in developing survival and dispersion models of outdoor atmospheric bacteria and microbial pesticides.

Solar Radiation Is Shown to Select for Pigmented Bacteria in the Ambient Outdoor Atmosphere

Abstract— The percentage of pigmented to total bacteria in the outdoor atmospheric population was studied in the field and in controlled laboratory experiments to evaluate the effects of solar radiation (SR) on bacterial survival. The field experiments showed that the percentage of pigmented bacteria positively correlated with SR activity during clear summer days. The percentage was lowest during darkness before dawn and around midnight (ca 33%) and as the SR increased during the day, gradually increased to a maximum of ca 50–60% at noontime to early afternoon and decreased thereafter. In the laboratory the ambient outdoor atmospheric bacteria impacted on culture plates were exposed to simulated SR and a germicidal light. With increased exposure, more nonpig‐mented bacteria were killed and the percentage of pigmented bacteria gradually increased. These observations suggest an inverse relationship between the atmospheric bacterial survival and the percentage of pigmented bacteria contained therein, thus supporting the notion that pigmentation might provide protection for outdoor atmospheric bacteria from sunlight damage. As a consequence, viable pigmented bacteria (and other UV‐resistant forms) in the atmosphere could be enriched under areas of stratospheric ozone depletion.

Effect of several stress factors on the susceptibility of the predatory insect, Chrysoperla carnea (Neuroptera: Chrysopidae), to the fungal pathogen Beauveria bassiana

Abstract Temperature, starvation, and nutrition stresses, applied singly and in combination, significantly affected the susceptibility of Chrysoperla carnea to Beauveria bassiana and varied in effectiveness according to insect age and gender. The nutrition stress caused the most significant increase in adult and larval mortality and larval developmental failure. Larval mortality and developmental failure were also increased by the starvation stress. The temperature stress affected C. carnea mortality only when used in combination with nutrition and/or starvation. Possible mechanisms for the effects of the stresses on C. carnea response to B. bassiana are discussed.

Field Evaluation of Beauveria bassiana: Its Persistence and Effects on the Pea Aphid and a Non-target Coccinellid in Alfalfa

Several strains of the entomopathogenic fungus Beauveria bassiana have been considered for use as microbial insecticides. Experimental sprays were conducted in an alfalfa field with an aphid-derived strain of B. bassiana to determine its persistence and its effects on pea aphids, Acyrthosiphon pisum (Homoptera: Aphididae) and a non-target aphid predator, Hippodamia convergens (Coleoptera: Coccinellidae). B. bassiana conidia persisted in the field for at least 28 days, when approximately 10% of the original inoculum was still present. In the lower canopy, more conidia were present than on other plant parts and they persisted longer on the leaves in this location. However, conidia were still abundant in the upper canopy, where 97.9% of the aphids and 95.5% of H. convergens larvae were found. Thus, both insect species were exposed to the fungus for at least 1 month. However, pea aphid populations were not affected by the fungus. The predators incidence was reduced by 75-93% (depending on application rate) e...

Instrumentation Used with Microbial Bioaerosols

Bioaerosol monitoring is a rapidly emerging area of industrial hygiene that is finding increased use and overuse. It is often used in conjunction with indoor environment quality investigations, infectious disease outbreaks, and agricultural health investigations. Bioaerosol monitoring includes the measurement of viable (culturable and nonculturable) and nonviable microorganisms in both indoor (e.g., industrial, office, or residential) and outdoor (agricultural and general air quality) environments. In general, indoor bioaerosol sampling need not be performed if visible growth is observed. Contamination (microbial growth on floors, walls, or ceilings, or in the HVAC system) should be remediated. If personnel remain symptomatic after remediation, air sampling may be appropriate, keeping in mind that negative results are quite possible and they should be interpreted with caution. Other exceptions for which bioaerosol sampling may be appropriate include epidemiological investigations, research studies, or if indicated after consultation with an occupational physician and an immunologist.