David G. Schmale

Accurate tracking and measurement of pollen dispersal in the atmosphere are essential for assessing cross-pollination risks, particularly in the case of genetically engineered (GE) crops. We conducted a series of unique release-recapture field studies with GE switchgrass in Oliver Springs, TN, USA. Two hundred transgenic switchgrass plants ( Panicum virgatum L. “Performer”) were planted at the center of a clear-cut field, with one block of 100 plants expressing orange fluorescent protein (OFP) under a switchgrass ubiquitin promoter (PvUBI1) and another block of 100 plants expressing OFP driven by a maize pollen-specific promoter (Zm13). Pollen was sampled from the atmosphere using fixed (ground-based) and mobile (drone-based) sampling devices at different distances from the source field, with Lagrangian stochastic dispersal simulations run for sampling periods using high-resolution wind measurements. The pollen emission rate was estimated by combining simulated and measured pollen concentrations, and strong diurnal trends were observed. Diurnal emission rate trends were positively correlated with wind speed, temperature, and vapor pressure deficit, while negatively correlated with relative humidity. In low-wind meandering conditions, incorporating changing wind direction into the dispersal modeling improved pollen emission rate estimation and model-measurement comparisons. This study assesses the effectiveness of high- and low-volume pollen samplers in relation to source strength up to 1 km from the source, enhancing understanding of pollen measurement techniques. Additionally, it is a proof-of-concept for drone-based pollen sampling and GMO pollen tracking using fluorescence measurements. Results from our experiments have significant implications for cross-pollination risk assessment, prediction, and management of airborne allergens.

Microplastics (MPs) are increasingly detected throughout the atmosphere, raising questions about their persistence and influence on cloud-relevant ice nucleation processes. Recent studies suggest that MPs may act as ice-nucleating particles (INPs), potentially enhanced by biological colonization. Here, we quantify the ice nucleation activity (INA) of polystyrene (PS) and polyethylene (PE) MPs before and after surface aging and microbial colonization. Strains of Pseudomonas syringae, spanning a range of INA, were cultured onto pristine and aged 100 μm PS and PE MPs. Uncolonized MPs (0.5 to 100 μm PS; 100 μm PE) exhibited INA, with median freezing temperatures ranging from -21.0 °C to -23.8 °C. Hydrothermal and photooxidation exposure, produced small, statistically insignificant increases in freezing temperature. PE MPs nucleated ice at higher temperatures than PS MPs, while the size of MPs did not appear to impact mean freezing temperatures. However, biofilm colonization increased median freezing temperatures by ∼6.5 °C (p < 0.0001) and enhanced INA relative to noncolonized MPs and cells alone. These results indicate that atmospherically relevant MPs modified by aging and microbial growth exhibit elevated INA, highlighting an under represented pathway by which MPs may influence cloud microphysics.

There is a growing need for scalable and high-throughput model systems to study plant-pathogen interactions and fungal secondary metabolite production. This research addresses that need by exploring the use of callus culture as a proxy for whole-plant infection dynamics and mycotoxin biosynthesis. Both callus and intact Arabidopsis thaliana plants were inoculated with the fungal pathogen, Fusarium graminearum. Disease progression in plants was evaluated using a visual Fusarium-Arabidopsis Disease (FAD) rating system, while ergosterol, a marker of fungal biomass, was quantified in callus. The mycotoxin, deoxynivalenol, (DON) was measured in both plants and callus. Three A. thaliana accessions with known differences in susceptibility were assessed at 7, 14, and 21 days post-inoculation (DPI). In all greenhouse experiments, inoculated plants exhibited symptoms and signs of infection including mycelial growth, drying, and constriction. The three A. thaliana accessions varied significantly in mean FAD ratings (P = 0.03), when controlling for timepoint and experiment. DON was detected in flower and seed samples from infected A. thaliana plants. Inoculated calli exhibited symptoms of infection, and DON was measured in some but not all samples. Inconsistent DON detection may reflect detoxification by other fungi or the plants themselves. Mean ergosterol concentrations varied significantly across callus of different accessions (P = 0.02), when controlling for timepoint and experiment. These findings highlight distinctions in disease markers based on accession-specific susceptibility and time post-inoculation. Collectively, the results support the potential of callus culture as a simplified yet informative system for studying plant-pathogen interactions and developing phytosensors for fungal pathogen detection in the future.

Shorter travel distance, lower solar radiation and higher relative humidity create a more suitable environment for the survivability of microorganisms onboard dust plumes traveling across the Atlantic Ocean from December to February.

Ground-based sensors were used to study HAB-associated particles in the atmosphere, and a drone was used to measure vertical profiles of wind.

Cyanobacterial harmful algal blooms (cHABs) have the potential to adversely affect public health through the production of toxins such as microcystins, which consist of numerous molecularly distinct congeners. Microcystins have been observed in the atmosphere after emission from freshwater lakes, but little is known about the health effects of inhaling microcystins and the factors contributing to microcystin aerosolization. This study quantified total microcystin concentrations in water and aerosol samples collected around Grand Lake St. Marys (GLSM), Ohio. Microcystin concentrations in water samples collected on the same day ranged from 13 to 23 μg/L, dominated by the d-Asp³-MC-RR congener. In particulate matter 2.5), microcystin concentrations up to 156 pg/m³ were detected; the microcystins were composed primarily of d-Asp³-MC-RR, with additional congeners (d-Asp³-MC-HtyR and d-Asp³-MC-LR) observed in a sample collected prior to a storm event. The PM size fraction containing the highest aerosolized MC concentration ranged from 0.44 to 2.5 μm. Analysis of total bacteria by qPCR targeting 16S rDNA revealed concentrations up to 9.4 × 10⁴ gc/m³ in aerosol samples (≤3 μm), while a marker specific to cyanobacteria was not detected in any aerosol samples. Concentrations of aerosolized microcystins varied even when concentrations in water were relatively constant, demonstrating the importance of meteorological conditions (wind speed and direction) and aerosol generation mechanism(s) (wave breaking, spillway, and aeration systems) when evaluating inhalation exposure to microcystins and subsequent impacts on human health.

Bacteria from the Pseudomonas syringae complex (comprised of at least 15 recognized species and more than 60 different pathovars of P. syringae sensu stricto) have been cultured from clouds, rain, snow, streams, rivers, and lakes. Some strains of P. syringae express an ice nucleation protein (hereafter referred to as ice+) that catalyzes the heterogeneous freezing of water. Though P. syringae has been sampled intensively from freshwater sources in the U.S. and France, little is known about the genetic diversity and ice nucleation activity of P. syringae in other parts of the world. We investigated the haplotype diversity and ice nucleation activity at −8 °C (ice+) of strains of P. syringae from water samples collected with drones in eight freshwater lakes in Austria. A phylogenetic analysis of citrate synthase (cts) sequences from 271 strains of bacteria isolated from a semi-selective medium for Pseudomonas revealed that 69% (188/271) belonged to the P. syringae complex and represented 32 haplotypes in phylogroups 1, 2, 7, 9, 10, 13, 14 and 15. Strains within the P. syringae complex were identified in all eight lakes, and seven lakes contained ice+ strains. Partial 16S rDNA sequences were analyzed from a total of 492 pure cultures of bacteria isolated from non-selective medium. Nearly half (43.5%; 214/492) were associated with the genus Pseudomonas. Five of the lakes (ALT, GRU, GOS, GOL, and WOR) were all distinguished by high levels of Pseudomanas (p ≤ 0.001). HIN, the highest elevation lake, had the highest percentage of ice+ strains. Our work highlights the potential for uncovering new haplotypes of P. syringae in aquatic habitats, and the use of robotic technologies to sample and characterize microbial life in remote settings.

The adverse economic impacts of harmful algal blooms can be mitigated via tailored forecasting methods. Adequate provision of these services requires knowledge of the losses avoided, or, in other words, the economic benefits they generate. The latter can be difficult to measure for broader population segments, especially if forecasting services or features do not yet exist. We illustrate how stated preference tools and choice experiments are well suited for this case. Using as example forecasts of respiratory irritation levels associated with airborne toxins caused by Florida red tide, we show that 24-hour predictions of spatially and temporally refined air quality conditions are valued highly by the underlying population. This reflects the numerous channels and magnitude of red tide impacts on locals’ life and activities, which are also highlighted by our study. Our approach is broadly applicable to any type of air quality impediment with risk of human exposure.

Little is known about the transport and fate of aerosolized particles associated with harmful algal blooms (HABs). An Airborne DROne Particle-monitoring System (AirDROPS) was developed and used to monitor, collect, and characterize airborne particles over two HABs in Grand Lake St Marys (GLSM) and Lake Erie (LE), Ohio USA in August 2019. The AirDROPS consisted of an impinging device (ID) and an optical particle counter (OPC) mounted on a large commercial quadcopter (DJI Inspire 2). The sensor package was mounted above the airframe to limit the effects of propeller downwash that can corrupt measurements taken below the drone. Nineteen flights were conducted 10 m above water level (AWL) at GLSM, and five flights were conducted 10 m AWL at LE. The sampling height was chosen to minimize the effects of propwash on aerosolization from the lake surface. One intercomparison flight was conducted at GLSM over land adjacent to a sonic anemometer mounted on the top of a flagpole 15 m above ground level (AGL). Particle counts generally decreased from morning to afternoon flights, ranging from >4000 in the morning to 4000 below 4 m s⁻¹ to −1. Flow cytometry was used to image particles trapped in a liquid impinger onboard the AirDROPS. Sixty percent (15/25) of the impinger samples contained at least one biotic (fluorescent) object. Impinger samples were also analyzed for a suite of potential cyanotoxins using liquid chromatography-mass spectrometry (LC-MS/MS), but no cyanotoxins were detected in any of these air samples (water samples collected during a similar time contained greater than 20 μg L⁻¹ microcystins). Additional work is needed to understand the environmental factors associated with the potential aerosolization and transport of cyanobacterial cells and toxins in aquatic environments.