Biodegradation by bacteria in clouds: An underestimated sink for some organics in the atmospheric multiphase system

Abstract

Abstract. Water-soluble organic compounds represent a significant fraction of total atmospheric carbon. The main oxidants towards them in the gas and aqueous phases are OH and NO3 radicals. In addition to chemical solutes, a great variety of microorganisms (e.g. bacteria, viruses, fungi) has been identified in cloud water. Previous lab studies suggested that for some organics, biodegradation by bacteria in water is comparable to their loss by chemical processes. We perform model sensitivity studies over large ranges of biological and chemical process parameters using a box model with a detailed atmospheric multiphase chemical mechanism and biodegradation processes to explore the importance of biodegradation of organics in the aqueous phase. Accounting for the fact that only a small number fraction of cloud droplets (~ 0.0001–0.001) contains active bacteria cells, we consider only a few bacteria-containing droplets in the model cloud. We demonstrate that biodegradation might be most efficient for volatile organic compounds (VOC) with intermediate solubility (~ 104 ≤ KH(eff) [M atm−1] ≤ 106, e.g., formic and acetic acids). This can be explained by the transport limitation due evaporation of organics from bacteria-free droplets to the gas phase, followed by the dissolution into bacteria-containing droplets. For non-volatile organics (NVOC), such as dicarboxylic acids, the upper limit of organic loss by biodegradation can be approximated by the amount of organics dissolved in the bacteria-containing droplets (

The Biogeography of Dust in the Eastern Mediterranean

“…Accordingly, we found that along with genes associated with the biodegradation of organic contaminants, methane metabolism genes were also positively correlated with PM 10 concentration, as well as genes associated with glyoxylate and dicarboxylate metabolism, which includes formate metabolism. All or some of these substances might be relevant to metabolic activity in the atmosphere due to their biodegradation, as suggested in other studies, 65,78 as well as in dust-affected terrestrial and marine regions.…”

“…Recent evidence on the possible metabolic activity of bacteria in the atmosphere suggests that speci c carbon sources are likely to sustain bacteria, e.g., formate, acetic acid and ethanol. 8,65,78 Moreover, it was suggested that bacterial metabolism might also affect cloud or even atmospheric chemistry. 65,102 Our results suggest that if dust storms carry viable bacteria, they may be metabolically relevant for atmospheric chemical cycles and may spread these bacteria globally.…”

“…Previous studies have suggested that the adaptation of airborne microorganisms to atmospheric conditions would bene t from the presence of functions such as UV resistance, osmotic stress resistance, envelope stress resistance, sporulation, methane oxidation, formate degradation, acetic acid degradation and oxidative stress resistance. 3,8,64,65 Thus, these studies targeted these functions in metagenomic as well as metatranscriptomic analyses of different atmospheric samples. Consistent with this, we focused on these functional genes, as well as many other environmentally relevant functional genes, in our analysis to better de ne the contribution of mineral dust to the potential functionality of the aerobiome.…”

Ocean Aerobiology

“…A major unknown is what proportion of the marine aerobiota is metabolically active and whether this has a significant effect on aerosol-cloud interactions and the processing of marine DOM in the atmosphere. Cloud water contains DOM, which could support microbial metabolism (Khaled et al, 2020), including the remineralization of DOM back to carbon dioxide. Ervens and Amato (2020) estimated that the global loss of DOM in clouds is 0.008-0.011 Pg C yr −1 , which is insignificant when compared with the 662 Pg C as DOM in the ocean (Hansell et al, 2009), or estimates of annual oceanic photosynthetic production of 45-55 Pg C yr −1 (Longhurst et al, 1995;Field et al, 1998;Carr et al, 2006;Westberry et al, 2008).…”