Skip to content

Bioaerosols in the Earth System 2011: symposium summary & video interviews


In July of this year, a one-day symposium on Bioaerosols in the Earth System took place as part of the 25th General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Melbourne, Australia.  This meeting brought together part of the growing interdisciplinary community of scientists who met for the first time in 2006 in Avignon, France to put their efforts together to elucidate how biological aerosols impact atmospheric processes. 

For those of you who could not attend the IUGG General Assembly in Melbourne, as convenor I put together an annotated list of the presentations and some comments about the general discussion that took place in this session.  Email addresses of speakers are indicated (replace -AT- with the logogram @ ) in case you want to ask them more specific questions about their work.  In the summary presented below, I have also included short video interviews of some of the speakers and other researchers working on bioaerosols.  Click on the links to see the scientists talk about their work and respond to some impromptu questions about the future of research on Bioaerosols in the Earth system.  

Participation of some of the scientists in the symposium was possible thanks to deferment of their registration fees by the IUGG organizers and financial aid for travel costs from the US National Science Foundation, Division of Atmospheric and Geospace Sciences.


ON THE WAY TO IUGG-2011, I interviewed David Sands (Montana State University,, co-organizer of the first interdisciplinary meeting on the interaction of bioaerosols with atmospheric processes (Sands-video)


DURING THE IUGG-2011 session on Bioaersols in the Earth System, oral presentations included:

-Direct measurements of bioaerosol fluxes into the atmosphere: relevance and challenges.

      Yves Brunet, INRA, Bordeaux, France

Measuring the flux of bioaerosols from a source is a difficult challenge. Little progress has been made since the work of Lindemann et al and of Lighthart et al in the 1980’s and 1990’s. A review of all possible methods shows that one solution would be to adapt a technique called the “relaxed eddy accumulation”. It is based on a conditional sampling of the air, depending on the sign of the instantaneous vertical wind speed, and allows standard concentration samplers to be used in place of fast-response sensors. The experience gained in developing a first prototype shows that the key issue is to achieve a high enough signal-to-noise ratio in the concentration measurements. There is reasonable hope that this goal can be reached soon. (Brunet-video)  You’ll need to turn up the volume for this one.


-Understanding global transport of bacteria into the atmosphere.

       Susannah Burrows, Max Planck Institute of Chemistry, Mainz, Germany            


Different ecosystems are likely to emit different quantities of bacteria into the atmosphere.  Data on aerosol concentrations of bacteria over different ecosystems have been useful in making the first estimates of overall transport of bacteria in the atmosphere.  The utility of these data is improved when they are coupled to estimations of potential residence time in the atmosphere.  Bacteria generally have rather long residence times because of their small size, but those emitted into the air in the spring and summer are likely to have even longer residence times than those emitted in the winter.  Estimates of transport will be improved as data for microbial flux and residence time accumulate.  (Burrows-video)


-Diatoms in the snow in the Windmill Islands: sources and implications.

       Amy Budgeon, University of Queensland, Australia

Aeolian-deposited marine diatoms were found in snow in the WindmillIslands, Antarcticaafter an anomalous weather event.  From the species assemblage a source region with open water and the presence of some sea ice was determined.  This was confirmed by back-trajectory modelling and the presence of the sea-ice mineral ikaite (CaCO3.6H2O) in the snow. This shows potential for this method to be used in ice core palaeosource determination.


-Occurrence of the ice nucleation active bacterium Pseudomonas syringae in precipitation is linked to air mass properties and their trajectories.

      Cindy Morris, INRA, Avignon, France

P. syringae is found in well over half of the rain events that occur in southern France, but it is present much less frequently in fresh-fallen snow than we had originally thought.  The climatic parameters of the air masses that bring precipitation, and in particular temperature and the region of origin of the air mass, seem to be overriding factors in the presence of this bacterium in precipitation.  (Morris-video)


-Parameterizing bioaerosol emissions and interactions with clouds : current issues in models on different scales

     Corinna Hoose, Karlsruhe Institute of Technology, Karlsruhe, Germany    


The outcome of the different efforts to model the impact of bioaerosols on cloud processes, and particularly that of ice nucleation active particles including bacteria and fungi, is very sensitive to a range of model parameters and assumptions.  There is an important need for more field measurements of the abundance and dynamics of biological ice nucleators in the atmosphere in order to better constrain the models.  (Hoose-video)


-Crops and debris as potential sources of high temperature ice nuclei.

                Tom Hill, Universityof Wyoming, Laramie, WY, USA

Detection of ice nucleation-active bacteria in agricultural fields, based on molecular biological techniques that target the gene coding for the ice nucleation protein in the DNA of bacteria related to Pseudomonas syringae, suggests that these bacteria are 10 to 100’s times more abundant than previously revealed with techniques used in classical microbiology.  Although the bacteria detected might not necessarily be living and able to multiply, the protein carried on their cells might be ice nucleation active and able to play a role in atmospheric processes.


-Cloud condensation and ice nucleation activity of bacteria isolated from cloud water.

                Caroline Oehm: KarlsruheInstitute of Technology, Karlsruhe, Germany    


In the AIDA cloud simulation chamber in Karlsruhe, Germany, the capacity of strains of Pseudomonas syringae and P. fluorescens to cause ice crystal formation in simulated clouds has been tested.  After bacterial suspensions are injected into the chamber, two types of particle fractions can be found in the chamber: a fraction containing particles about 1 µm in diameter and particles less than half that size.  Both of these populations of particles are ice nucleation active at relatively warm temperatures suggesting a role for cell fragments as ice nuclei.


-The ice nucleation ability of pollens and fungal spores.

        Bernhard Pummer,ViennaUniversity of Technology, Austria. 


The ice nucleation activity of bacteria is due to a heat-labile protein that is intimately associated with the outer membrane of the cell.  The ice nucleation properties of certain fungal spores and pollen react differently to heat and chemical treatments than those of bacteria.  The ice nucleation activity of pollen – and of birch and pine in particular – resists heat treatment up to 170°C.  The factor that is ice nucleation active can also be washed off.  The ensemble of the observations by Bernhard’s team make carbohydrates or organic or inorganic polymers likely candidates responsible for the ice nucleation activity.


-Effect of bacterial ice nuclei on the frequency and intensity of lightning activity inferred by the BRAMS model.

                Fabio Gonçalves, University of Sao Paulo, Brazil

In an atmospheric model adapted to Brazilian environmental conditions, ice nucleators in clouds were parameterized according to data for the abundance of the ice nucleation active bacterium Pseudomonas syringae in clouds.  The amount of lighting resulting from the ice generated by the bacterium was then estimated in the model.


-Overview of physical and chemical approaches for direct detection of bioaerosols.

                Alex Huffman, Max Planck Institute of Chemistry, Mainz, Germany 


The utility of microscopy and molecular (PCR) detection for bioaerosols are well recognized.  But these techniques require relatively costly and laborious post-collection analyses.  A variety of recent developments in techniques such as  laser-induced fluorescence (LIF) and aerosol mass spectrometry, among many others, are enabling the improved measurement of the concentration and properties of bioaerosols in real-time.  (Huffman-video)


-Fungal diversity and biogeography in air.

            Janine Fröhlich, Max Planck Institute of Chemistry, Mainz, Germany 


Fungi in the Ascomycota and Basidomycota are among the most abundant in the atmosphere.  However, extensive air sampling at sites on multiple locations revealed that Ascomycota are dominant in the air over oceans whereas Basidiomycota dominate in the air over continents, and particularly in the autumn when wood rot fungi – the most abundant organisms in this group – produce their fruiting bodies.  (Fröhlich-video)


-Phylogenetic analysis of long range transported bacteria isolated from Asian dust aerosols.

                 Teruya Maki, CollegeOf Science And Engineering, Kanazawa University, Japan 


Asian desert dusts transport bacteria across Chinato Japanand Korea.  In an attempt to trace the dissemination of bacteria in these desert dusts, halotolerant bacteria were isolated from aerosols.  This group of bacteria was targeted because they are the ones most likely to resist the stress of transport with oceanic winds.  The ensemble of the halotolerant bacteria isolated were Bacillus spp., and those in the arrival area (Japan) were genetically very similar to those from the suspected source (Asian deserts).  Microscopic analysis of dusts particles revealed that cells of Bacillus spp. were bound to mineral particles.


-Microbial implication in atmospheric chemistry.

                 Mickael Vaitilingom, Université Blaise Pascal, Clermont-Ferrand, France


Until recently, photochemistry has been considered the main process responsible for oxidation of organic substances in clouds and aerosols.  Kinetic studies of the metabolism of atmospheric organic acids by bacteria found in clouds suggests that bacterial-mediated chemical reactions might be occurring at an order of magnitude similar to that of photochemical processes.


-Research priorities for climate effects of bioaerosols.

                Keith Bigg, independent scientist retired from CSIRO, Australia

After 40 years of research in meteorology and atmosphere physics at CSIRO in Australia and another 20 years as a free-lance scientist, Keith has put together compelling observations that suggest that there is a system of feedback that markedly influences precipitation cycles across the Australian continent.  These intriguing data re-enforce one of the founding motivations of the interdisciplinary network of researchers attending the conference – to elucidate a biofeedback process that was suspected to occur between ice nucleation active bacteria and rain and that had been christened “bioprecipitation” in the early 1980’s.  To investigate such a process on a global scale, Keith recommends that ice nucleation detection methods be further developed, and in particular to account for the time scale of the ice induction process in clouds that can occur on the scale of minutes rather than the fractions of seconds used to evaluate the ice nucleation activity of particles currently deployed in ice nucleation detectors.  (Bigg-video)


-Mapping the interdisciplinarity of research on the role of microbial aerosols in atmospheric processes

                 Cindy Morris, INRA, Avignon, France

In 2006 an interdisciplinary network was launched around the theme of this current IUGG symposium.  What is the current state of interaction among the different disciplines represented in this network?  Are they working together to explore the interaction of bioaerosols with atmospheric processes?  To map the interaction of the different disciplines and to identify different sub-networks of partners, the Web of Science publication data base was consulted with a broad set of key words and further sorted manually leading to the identification of 110 pertinent papers published in the period 2006 – mid 2011.  Disciplinary competence of each author was classified into 4 categories of the life sciences (LS) and 6 categories of physical sciences, math and engineering (PSE) based on responses of authors to inquiries.  About 50% of the papers were co-authored by representatives of both LS and PSE; for the remaining half there was an equal rate of publication by LS or PSE authors alone.  The main network of interaction involved collaborations among research labs in Europe and North America; a group of Chinese research labs working on the Tibetan plateau constituted a separate network.



About 30 minutes was allotted for general discussion at the end of the symposium (there is never enough time for discussion). 

Norm Sleep of Stanford ( initiated very interesting discussion about the evolutionary history of micro-organisms adapted to a lifestyle that included prolonged periods of being airborne.  He is particularly interested in using geological records to constrain molecular phylogeny.  Such an approach has been used to construct the concept of Terrabacteria (see the Wikepedia entry on this subject:  He believes that there is ample geological justification to looking for deeply rooted adaptations to airborne survival. 

The second part of the discussion focused on questions that we saw as important for research perspectives on bioaerosols.  Three points were raised for which we identified a moderator who would put into place working groups.  The first emanates from several of the presentations at this meeting and from some of the historical foundations of why we are interested in the interaction of bioaerosols and atmospheric processes.  Feedbacks between bioaerosols and the atmosphere are likely to be numerous.  One of the earliest possible feedbacks to be evoked in the 1980’s and again at this meeting was the cycle of “bioprecipitation” involving ice nucleation-active bacteria from plants and rainfall.  Cindy Morris will put together a working group with the objective of sketching out and ranking the research importance of possible feedbacks.  The other two working groups will look into the assumptions underlying what we currently believe about processes linked to bioaerosol-atmosphere interactions.  Tom Hill will head up a group whose objective will be to list what we strongly believe about atmospheric processes and the assumptions underlying these beliefs.  Anne-Marie Delort will head up a group on a similar subject, but which will be focused on atmospheric chemistry and the currently viewed dominant role of radical chemistry.

POST-SYMPOSIUM, I interviewed a couple of the very dynamic actors in our network:

Anne Marie Delort (Université Blaise Pascal, Clermont-Ferrand, France, talks about the potential role of micro-organisms in oxidative processes in clouds.  Her description of clouds as a bacterial bus is scintillating.  (Delort-video).

As an atmosphere physicist, Zev Levin (Tel Aviv University, Israel, has investigated for many years the potential role of ice nucleation active bacteria in processes leading to rainfall and has been instrumental in the emergence of the interdisciplinary research network.  In this interview, Zev talks about his vision of what we know and what we need to explore further. (Levin-video)


No comments yet

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: