Microorganisms isolated from the water phase of tropospheric clouds at the Puy de Dôme: major groups and growth abilities at low temperatures

Abstract

This work constitutes the first large report on aerobic cultivable microorganisms present in cloud water. Seven cloud-event samples were collected at the Puy de Dôme summit, and cultivation was performed leading to the isolation of 71 bacterial, 42 fungal and 15 yeast strains. Most of the fungi isolated were of Cladosporium or Trametes affiliation, and yeasts were of Cryptococcus affiliation. Bacteria, identified on the basis of their 16S rRNA gene sequence, were found to belong to Actinobacteria, Firmicutes, Proteobacteria (Alpha, Beta and Gamma subclasses) and Bacteroidetes phyla, and mainly to the genera Pseudomonas, Sphingomonas, Staphylococcus, Streptomyces, and Arthrobacter. These strains appear to be closely related to some bacteria described from cold environments, water (sea and freshwater), soil or vegetation. Comparison of the distribution of Gram-negative vs. Gram-positive bacteria shows that the number of Gram-negative bacteria is greater in summer than in winter. Finally, a very important result of this study concerns the ability of half of the tested strains to grow at low temperatures (5 degrees C): most of these are Gram-negative bacteria, and a few are even shown to be psychrophiles. On the whole, these results give a good picture of the microbial content of cloud water in terms of classification, and suggest that a large proportion of bacteria present in clouds have the capacity to be metabolically active there. This is of special interest with respect to the potential role of these microorganisms in atmospheric chemistry.

ANaganishiain high places: functioning populations or dormant cells from the atmosphere?

“…in the Northwest USA (Smith et al 2012) and from 1,464 m.a.s.l. in Western Europe (Amato et al 2007), showing that these fungi are still viable after aerial transport. From a culture-independent perspective, N. albida and other Naganishia OTUs were detected in Israeli dust storms from 2012 and 2013 (Katra et al 2014).…”

Measurements and modeling of surface–atmosphere exchange of microorganisms in Mediterranean grassland

“…Furthermore, microorganisms can be found in cloud water droplets. Water sampled from clouds over alpine regions in France and Austria contained about 2 × 10 4 mL −1 of bacteria (Amato et al, 2007;Bauer et al, 2003), while fungi were at least an order of magnitude lower. Different bacterial species were also found in fog droplets of the Po Plain in Italy (Fuzzi et al, 1997), as well as in clouds over Scotland (Ahern et al, 2007).…”

Microbiology and atmospheric processes: research challenges concerning the impact of airborne micro-organisms on the atmosphere and climate

“…This Gram-negative plant pathogenic bacterium is not the most abundant of the micro-organisms present in the atmosphere (Lighthart, 1997), but it will very likely become one of the most highly studied organisms with regard to potential impact on atmospheric processes. This is due in particular to its well-known activity as an ice nucleator at temperatures near zero (Möhler et al, 2007; reviewed by Morris et al, 2004), and to its significant upward flux in the atmosphere (Lindemann et al, 1982), its presence in clouds (Amato et al, 2007b;Sands et al, 1982), its potential activity as a cloud condensation nucleus (Snider et al, 1985), and recent observations about its abundance in snow and rain . Furthermore, all strains of P. syringae isolated from snow and rain by Morris and colleagues were ice nucleation active at temperatures between −2 • C and −6 • C whereas not all strains of this bacterium isolated from various other substrates (including plants, water and epilithic biofilms) were active as ice nucleators .…”

“…as well as the plant associated fungus Fusarium avenaceum (Pouleur et al, 1992) are known to be ice nucleation active but very little, relative to P. syringae, is known about their abundance in the atmosphere. Amato and co-workers have recently reported the isolation of F. avenaceum from clouds at about 1450 m altitude (Amato et al, 2007b) in central France. Algae are also known to be readily disseminated in the air and a few species are ice nucleation active at temperatures as warm as −6 • C (Worland and Lukesova, 2000).…”