Can the diverse bacterial community grow on dissolved organic matter in a storm
cloud?
T.Š. Temkiv1,2,3, K. Finster2, T. Dittmar4, B.M. Hansen1, R. Thyrhaug5, N.W. Nielsen6 and U.G. Karlson1
1
Department of Environmental Science, Aarhus University, 8000 Aarhus, Denmark
2
Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark
3
Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark
4
Max Planck Research Group for Marine Geochemistry, University of Oldenburg, 26129 Oldenburg, Germany
5
Department of Biology, University of Bergen, 5020 Bergen, Norway, opus posthum
6
Danish Meteorological Institute, 1000 Copenhagen, Denmark
Keywords: atmospheric microorganisms, bioaerosols, storm clouds, cloud chemistry
Introduction
Due to their inaccessibility and extremely
short lifetimes, storm clouds are among the least
studied habitats of the atmosphere. We have carried
out the first comparative study, analysing 50
individual large hailstones as replicate samples, in
order to study the dissolved organic matter (DOM) as
well as the microbiome of a storm cloud.
Methods
Catalytic high temperature combustion was
used to determine the concentrations of dissolved
organic carbon (DOC) and total dissolved nitrogen
(TDN). Ultrahigh-resolution mass spectrometry was
used to characterize DOM.
Bacterial density was analysed by flow
cytometry, while bacterial community composition
and diversity was assessed by both cultivationdependent and independent techniques. Phenotype
Microarrey plates were used to investigate the
metabolic potential of bacteria.
(60%) of detected compounds, and thus aerosols,
were derived from soils. The enrichment of plantassociated bacterial strains points at a positive
selection of microbes in the course of cloud
formation, which is likely a consequence of intrinsic
growth and survival properties of plant-associated
bacteria over microbes that are derived from other
habitats such as soils. In fact, analyzing the metabolic
potential of isolates, we found that they grew on a
diverse menu of organic compounds, and thus had an
opportunistic metabolic strategy (Temkiv et al.,
2012). In addition, they may be preadapted for
survival in the atmosphere, as they meet similar
stress factors, e.g. UV radiation and desiccation on
plant surfaces and in the atmosphere. Based on the
spectrum of biodegradable organics as well as
bacterial numbers and types, we conclude that storm
clouds likely contain metabolically active bacteria,
which affect the chemical makeup of the atmosphere.
Conclusions
The identification of ~3000 organic
compounds showed that less than 3% of the
compounds were suitable for microbial degradation.
However, the high concentrations of TDN (30 µM,
Q1–Q3 = 27–35 µM) and DOC (Me=179 µM, Q1–
Q3 = 132–220 µM) and the low bacterial densities
(Me=1973 cells/ml, Q1-Q3=1485-2960) indicated
that cloud water was a sparsely populated and
nutrient-rich microbial environment, where bacteria
could be metabolically active and multiply even if
only 3 % of DOM can be used by bacteria. As the
residence time of bacteria in cloud droplets is short,
only bacteria with opportunistic metabolic strategy,
i.e. having fast growth responses and fast growth
rates are likely to grow in clouds.
We found a diverse bacterial community with
representatives from 11 phyla that was dominated by
bacterial groups, coming from plant surfaces, a
pattern that was repeated in the cultivable fraction of
the community. Of the 424 culture strains the
majority was related to plant-associated genera
(Methylobacterium and Bradyrhizobium). The study
of DOM, on the contrary, showed that the majority
Figure 1. The molecular composition of dissolved
organic matter in hail.
Figure 2. Community composition in the storm
cloud.
Temkiv, T. S., Finster, K., Hansen, B. M., Nielsen,
N. W., & Karlson, U. G. (2012). FEMS Microbiol
Ecol, 81(3), 684-95.