AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Survival of Microorganisms to the Main Stress Factors Encountered in Clouds
Muriel Joly, Pierre Amato, Martine Sancelme, Mickaël Vaitilingom, Virginie Vinatier, Laurent Deguillaume, ANNE-MARIE DELORT, Clermont Université, Institut de Chimie de Clermont-Ferrand
Abstract Number: 8 Working Group: Bioaerosols: Characterization and Environmental Impact
Abstract Microorganisms are present in low altitude clouds at concentrations of ~104 bacteria per mL and ~103 fungi per mL. The microbiological monitoring of cloud water since 2003 at the puy de Dôme station (1465 m a.s.l., France) revealed the presence of recurrent microorganisms among the cultivable bacterial community: Pseudomonas spp. and Sphingomonas spp. notably were present in 55% and 45% of the samples collected respectively, and they represented 30% of the total heterotrophic bacteria cultivable at 17°C.
Clouds represent nearly obligate ways to the redeposition of micrometer-sized aerosols such as microorganisms onto the ground. Even though they are believed to be less aggressive environments than dry air, clouds likely remain harsh and probably operate as environmental filters to airborne microorganisms through various selection factors: solar radiation, oxidants, low temperature, acidity, osmotic shocks… etc…
In order to test this hypothesis, we selected five bacterial or yeast strains isolated from cloud water (Arthrobacter sp. AJ551167 ; Pseudomonas syringae AB001440 and HQ256872 ; Sphingomonas sp. HQ256831 ; Bullera armenica JF706549). These strains were chosen to offer a good representation of the particularities of the culture collection (Gram-positive and Gram-negative bacteria, pigmented or not, ice nucleation active or not). In parallel, an Escherichia coli strain (ATCC10798) was chosen as reference as none was found viable among our cloud samples.
The survival rates of each of these strains to four factors of stress consistent with the conditions encountered in clouds were investigated: osmotic shock, which occurrs when water vapour condenses or evaporates around airborne microorganisms, freeze-thaw cycles, presence of toxic compounds such as hydrogen peroxide, and solar radiation. The first results demonstrated that the strains isolated from clouds as well as E. coli were resistant to these treatments. Hence those selective factors are not sufficient to explain the composition of the viable community in clouds.