Hydroxy fatty acids in fresh snow samples from northern Japan: long-range atmospheric transport of Gram-negative bacteria by Asian winter monsoon

Abstract

Abstract. Hydroxy fatty acids (FAs) in fresh snow from Sapporo, one of the heaviest snowfall regions in the world, have been studied to ascertain the airborne bacterial endotoxin concentrations and their biomass. The presence of β-hydroxy FAs (C9–C28), constituents of Gram-negative bacteria (GNB), suggests long-range transport of soil microbes. Likewise, the occurrence of α- and ω-hydroxy FAs (C9–C30 and C9–C28, respectively) in snow reveals their contribution from epicuticular waxes and soil microorganisms. Estimated endotoxin and GNB mass can aid in assessing their possible impacts on the diversity and functioning of aquatic and terrestrial ecosystems, as well as lethal effects on pedestrians through dispersal of microbes. Air mass back trajectories together with hydroxy FAs unveil their sources from Siberia, Russian Far East and North China by the Asian monsoon. This study highlights the role of fresh snow that reduces the human health risk of GNB and endotoxin by scavenging from the air.

Hydroxy fatty acids in snow pit samples from Mount Tateyama in central Japan: Implications for atmospheric transport of microorganisms and plant waxes associated with Asian dust

“…Mass concentrations of total β ‐ and ω ‐hydroxy FAs in the dusty and nondusty layers (classified based on the visual appearance and nss‐Ca 2+ concentration, see Table ) of snowpacks collected in 2009 ( β ‐isomers: 1.04 µg kg −1 ; ω ‐isomers: 4.96 µg kg −1 ) and 2011 ( β ‐isomers: 0.62 µg kg −1 ; ω ‐isomers: 0.42 µg kg −1 ) were significantly higher than those reported in the fresh snow samples collected from Sapporo (northern Japan) during winter 2010 ( β ‐isomers: 0.24 µg kg −1 ; ω ‐isomers: 0.64 µg kg −1 ) and 2011 ( β ‐isomers: 0.18 µg kg −1 ; ω ‐isomers: 0.15 µg kg −1 ) [ Tyagi et al ., ]. This difference is due to a strong influence of the atmospheric input of Asian dust in the snowpack samples at the Murodo‐Daira site.…”

“…[] and Tyagi et al . []. In brief, melt snow samples (0.2–0.4 L) were first concentrated using a rotary evaporator under vacuum (<20°C) and then saponified with 1.0 M KOH in methanol at 80°C for 2 h. After the saponification, neutral components were removed by extraction with hexane/methylene chloride (10:1) and the remaining solution was acidified with 6 M HCl to form free carboxylic acids.…”

“…The LPS of GNB contains lipid A (an acylated diglucosamine head) fraction, which is present in the outer cell membrane of bacteria [ Pomorska et al ., ] and β ‐hydroxy fatty acids (FAs) with C‐numbers from 10 to 18. Thus, LPS mass can be estimated by a measurement technique based on a specific LPS molecule such as β ‐hydroxy FAs quantified by GC/MS [ Pomorska et al ., ; Reynolds et al ., ; Tyagi et al ., ]. LPS concentrations can be calculated using the mathematical expression as follows:…”

“…[] and Tyagi et al . []. Therefore, we have converted the sum of mass concentrations of β ‐hydroxy C 10 –C 18 FAs (nmol kg −1 of melt water) into equivalent dry cell weight of GNB (µg kg −1 of melt water) by normalizing to 15 nmol.…”

“…However, among culture‐independent techniques, the chemical marker‐based approach is considered as a suitable tool for the rapid and comparative analysis of bacterial dry biomass and their endotoxins in a variety of environmental samples. Furthermore, our previous studies showed that atmospheric hydroxy fatty acids (FAs) can be used as chemical markers to trace soil microbes and higher plant metabolites in aerosol and snow samples [ Tyagi et al ., , ]. These results indicate that higher atmospheric abundances of hydroxy FAs are associated with Asian dust episodes.…”