Diversity and Ice Nucleation Activity of Microorganisms Collected With a Small Unmanned Aircraft System (sUAS) in France and the United States.

Celia Jimenez-Sanchez,David G Schmale,Regina Hanlon,Craig Powers,Ken A Aho,Cindy E Morris

doi:10.3389/fmicb.2018.01667

Abstract

Many microbes relevant to crops, domestic animals, and humans are transported over long distances through the atmosphere. Some of these atmospheric microbes catalyze the freezing of water at higher temperatures and facilitate the onset of precipitation. We collected microbes from the lower atmosphere in France and the United States with a small unmanned aircraft system (sUAS). 55 sampling missions were conducted at two locations in France in 2014 (an airfield in Pujaut, and the top of Puy de Dôme), and three locations in the U.S. in 2015 (a farm in Blacksburg, Virginia, and a farm and a lake in Baton Rouge, Louisiana). The sUAS was a fixed-wing electric drone equipped with a remote-operated sampling device that was opened once the aircraft reached the desired sampling altitude (40–50 meters above ground level). Samples were collected on agar media (TSA, R4A, R2A, and CA) with and without the fungicide cycloheximide. Over 4,000 bacterial-like colonies were recovered across the 55 sUAS sampling missions. A positive relationship between sampling time and temperature and concentrations of culturable bacteria was observed for sUAS flights conducted in France, but not for sUAS flights conducted in Louisiana. A droplet freezing assay was used to screen nearly 2,000 colonies for ice nucleation activity, and 15 colonies were ice nucleation active at temperatures warmer than −8°C. Sequences from portions of 16S rDNA were used to identify 503 colonies from 54 flights to the level of genus. Assemblages of bacteria from sUAS flights in France (TSA) and sUAS flights in Louisiana (R4A) showed more similarity within locations than between locations. Bacteria collected with sUAS on TSA in France and Virginia were significantly different across all levels of classification tested (P < 0.001 for class, order, family, and genus). Principal Coordinates Analysis showed a strong association between the genera Curtobacterium, Pantoea, and Pseudomonas from sUAS flights in Virginia, and Agrococcus, Lysinibacillus, and Paenibacillus from sUAS flights in France. Future work aims to understand the potential origin of the atmospheric microbial assemblages collected with sUAS, and their association with mesoscale atmospheric processes.

Highlights

Many microorganisms that impact the health of crops, domestic animals, and humans are transported over long distances through the atmosphere (Schmale and Ross, 2015)
The specific objectives of our work were to: (1) collect microbes from the lower atmosphere at several sites with a small unmanned aircraft system, (2) quantify culturable microorganisms from sUAS flights using different types of agar media to maximize the diversity of microorganisms detected, (3) determine the frequency of ice nucleation activity (INA) microbes collected with sUAS at −8◦C, (4) identify bacteria from sUAS missions using sequences from portions of 16S rDNA, and (5) explore associations of microbial diversity to the different flights (55), locations (Virginia, Louisiana, and France), and media (R4A, TSA, R2A, and CA)
Little is known about the transport, diversity, and ice nucleation activity of microorganisms in the lower atmosphere

Summary

Introduction

Many microorganisms that impact the health of crops, domestic animals, and humans are transported over long distances through the atmosphere (Schmale and Ross, 2015). The dispersal of these microbes in the atmosphere is comprised of a complex series of events (Isard and Gage, 2001) Such events include microbial life history stages (e.g., aerosolization, escape from terrestrial or aquatic environments, survival while airborne, deposition onto a suitable environment, etc.), that interact with biotic and abiotic factors (e.g., rainfall, air currents, UV radiation, etc.) that control dispersal (Isard et al, 2005). These events and factors change in time and space across large-scale biological and meteorological gradients, forming a framework to understand the aerobiological processes governing the spread of microorganisms in the atmosphere (Aylor, 1986; Schmale and Ross, 2015). It has been hypothesized that the INA phenotype emerged as an adaptation to harsh conditions in the atmosphere; freeze tolerance and/or microbes facilitate their own deposition from the atmosphere (with low nutrient concentration) to land (rich in nutrients) through the production of ice-nucleating proteins or macromolecules (Morris et al, 2014)

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