2011 - Cooperative Institute for Research in Environmental Sciences ...

Noah Fierer
Microbial Life in the Atmosphere
NATIONAL SCIENCE FOUNDATION, U.S. DEPARTMENT OF
AGRICULTURE, ENVIRONMENTAL PROTECTION AGENCY
Bacteria are abundant
in the atmosphere, with the
near-surface atmosphere
containing more than 106
bacterial cells per cubic
meter of air. Atmospheric
transport is
a key mode of microbial
dispersal,
and the transmission
of airborne
plant and animal
pathogens can
significantly affect
ecosystems,
agriculture and
human health. For
example, recent
work implicates
bacteria found in
outdoor air—rather than pollen or fungi—as being one of
the dominant triggers of allergies and asthmatic reactions in
many locations. In addition, recent evidence suggests that airborne
bacteria may be able to alter atmospheric dynamics by
facilitating atmospheric ice nucleation and cloud condensation.
Our ongoing work addresses two fundamental questions
regarding bacteria in the atmosphere:
1) What is the full extent of bacterial diversity in the nearsurface
atmosphere?, 2) How does the abundance, composition
and diversity of airborne bacterial communities change
seasonally and across the continental U.S.?
We have been addressing these questions with a series of
studies conducted across a range of sites including: the Colorado
Front Range, a mountaintop research facility in northern
Colorado (Storm Peak Laboratory, Figure 2) and metropolitan
areas across the Midwest. We used a range of molecular techniques,
including high-throughput pyrosequencing and flow
cytometry, to characterize bacterial diversity and cell abundances
in the collected air samples. We have analyzed more
than 400 individual air samples yielding the largest and most
comprehensive survey of airborne bacterial diversity conducted
to date. We have found that bacterial cells often represent
an unexpectedly large portion (typically more than 20 percent)
of total aerosol particles, with the average cubic meter of air
harboring more than 100 unique bacterial species. We observe
strong geographic and seasonal changes in airborne bacterial
community composition that are largely driven by changes in
land-surface characteristics.
We are currently expanding on this work to examine
airborne bacterial diversity across broader spatial and
temporal gradients in order to build predictive models of
airborne bacterial abundances and diversity. We also have
initiated a ‘citizen-science’ project, the MiASMA project
(Mapping and Integrated AnalySis of Microbes in the Atmosphere;
http://tinyurl.com/3tybvmt), to build an atlas of
airborne microbial diversity across the continental U.S.
Figure 1: Network analysis of the airborne bacterial communities collected
from the Storm Peak Laboratory. Individual samples are denoted
by the larger circles and color coded by season with the smaller black
dots indicating individual bacterial species. Lines indicate species shared
between samples. This plot not only shows the high levels of bacterial
diversity found in the collected air samples, but it also indicates that the
species composition changes seasonally.
Figure 2: Views of Storm Peak Laboratory (Steamboat, Colo., 3220 M.A.S.L.)
during each of the air-sampling campaigns (photos taken by R. Bowers).
CIRES Annual Report 2011 35