Bacteria in the global atmosphere – Part 1: Review and synthesis of literature data for different ecosystems

Abstract

Abstract. Bacteria are ubiquitous in the atmosphere, with concentrations of bacterial cells typically exceeding 1×104 m−3 over land. Numerous studies have suggested that the presence of bacteria in the atmosphere may impact cloud development, atmospheric chemistry, and microbial biogeography. A sound knowledge of bacterial concentrations and distributions in the atmosphere is needed to evaluate these claims. This review focusses on published measurements of total and culturable bacteria concentrations in the atmospheric aerosol. We discuss emission mechanisms and the impacts of meteorological conditions and measurement techniques on measured bacteria concentrations. Based on the literature reviewed, we suggest representative values and ranges for the mean concentration in the near-surface air of nine natural ecosystems and three human-influenced land types. We discuss the gaps in current knowledge of bacterial concentrations in air, including the lack of reliable, long-term measurements of the total microbial concentrations in many regions and the scarcity of emission flux measurements.

Characterization of free amino acids, bacteria and fungi in size-segregated atmospheric aerosols in boreal forest: seasonal patterns, abundances and size distributions

“…The highest amounts of fungal DNA were measured in late June (30 149 cells m −3 ), August (55 839 cells m −3 ) and early October (35 050 cells m −3 ). In general, the concentration levels of microorganisms vary seasonally and geographically but are estimated to be at the level of ∼ 10 4 -10 5 and ∼ 10 4 -10 5 m −3 for bacterial cells and fungal spores, respectively (Burrows et al, 2009b;Després et al, 2012;Spracklen and Heald, 2014). Our observations are consistent with the common trend when considering that low concentration levels are typically observed at rural locations.…”

“…However, on average the abundances did not differ significantly in different size fractions (ANOVA, p = 0.494). The size distribution observed is in line with that of Burrows et al (2009b), who summarized that the median aerodynamic diameter of particles containing bacteria is 4 µm at continental sites. The abundance of Pseudomonas varied with statistical significance between different months (ANOVA, p < 0.05) and between different size fractions (ANOVA, p < 0.001).…”

“…PBAPs are released from multiple sources, such as soil, vegetation and oceans, and they include, for example, pollen, plant fragments, spores, bacteria, algae and viruses. In recent years, the abundance and dispersal of microorganisms in the atmosphere have attracted more and more interest, mainly due to the underestimation of their abundance and their possible atmospheric impact (Jaenicke, 2005;Morris et al, 2011;Deguillaume et al, 2008;Burrows et al, 2009b;Estillore et al, 2016). It is estimated that globally PBAPs constitute ∼ 30 % of aerosol particles mass in the particles sized > 1 µm in urban and rural air .…”

Immersion freezing of ice nucleation active protein complexes

“…Burrows et al (2009) estimated that the mean bacterial concentrations in air over land are > 10 4 cells per m 3 , which is in the range of total ice nuclei (IN) concentrations in the atmosphere (10 2 − 10 5 per m 3 , Murray et al, 2012). Over agriculturally used areas, the number concentration of bacteria can be even higher (10 6 -10 9 bacteria m −3 given in Morris et al, 2004, and references therein), but the exact fraction of INA bacteria among all airborne bacteria remains poorly quantified.…”

Evidence of global-scale aeolian dispersal and endemism in isolated geothermal microbial communities of Antarctica

“…Aerosolized microbes may originate from agricultural fields 2 , sewage treatment centres 3 , geothermal springs 4 , any surface exposed to sufficient wind force 5 and large-scale volcanic eruptions 6 . Organisms that have been independently aerosolized or attached to dust particles can be transported thousands of kilometres, which presumably allows microbes to easily move between continents and hemispheres [7][8][9][10][11] .…”