Within the pervasive mist, a living presence resides, though fortunately, it leans towards the amicable.
Investigations conducted by scientists at Arizona State University and Susquehanna University have uncovered that microbial life thrives and proliferates within water droplets comprising fog, exhibiting concentrations on par with those found in oceanic environments.
While this revelation indicates that fog is not entirely devoid of microscopic organisms, these microbes are demonstrably contributing: evidence suggests they play a role in the degradation of atmospheric contaminants.
From terrestrial exhalations to stratospheric formations, it has long been acknowledged that microorganisms are prevalent in the atmosphere in substantial quantities.
However, uncertainty persists regarding whether these microorganisms are actively sustaining themselves in these aerial settings or are merely in transit between different ecosystems.
Fittingly, fog itself presents an even more enigmatic domain.
“There is a profound scarcity of understanding concerning the specific bacterial species inhabiting fogs, which can be conceptualized as atmospheric clouds at ground level,” states microbiologist Thi Thuong Thuong Cao, affiliated with Arizona State University (ASU).
To pursue this inquiry, the protagonists of the present study gathered atmospheric specimens on 32 separate instances spanning a two-year duration, encompassing periods preceding, during, and following fog events.
To mitigate the confounding influence of wind displacement on observational data, the team focused its examination on radiation fog, a meteorological phenomenon that develops in quiescent, still atmospheric conditions during the nocturnal hours.
Indeed, a considerable microbial community was identified within that cool morning atmosphere.
Bacteria were detected in less than one percent of the fog droplets. While this percentage might seem marginal, it equates to an average of approximately 1 million 16S rRNA gene copies – a widely recognized metric for estimating bacterial population size – per milliliter of moisture.
“When one aggregates all the constituent droplets, the microbial density mirrors that of marine waters,” observes microbiologist Ferran Garcia-Pichel, also from ASU.
To ascertain the identities of these microorganisms, the research group performed genetic analyses. These investigations revealed that members of the Methylobacterium genus were the predominant inhabitants.
Furthermore, these bacteria did not appear to be in a dormant state.
“If indeed they are undergoing proliferation, then these micro-droplets constitute a viable habitat. This represents a fundamental paradigm shift,” posits Ferran Garcia-Pichel.
In an examination of six fog events, the team ascertained that even after the dissipation of the fog, the ambient air retained approximately 45 percent more bacteria than was present at the identical location prior to the fog’s inception.
This observation strongly implies that the atmospheric conditions during fog formation are actively fostering bacterial reproduction.
“Through microscopic inspection, we confirmed that the bacteria were indeed increasing in size and undergoing cell division, indicative of active growth,” confirms Cao.
Methylobacteria are recognized for their metabolic capability to consume volatile carbon compounds such as formaldehyde, leading the researchers to hypothesize that these substances might be fueling their growth.
To validate this premise, the scientists incubated samples of fog water and monitored the temporal fluctuations in the concentrations of these volatile compounds.
As anticipated, these levels decreased, but the rate of consumption was unexpectedly rapid.
“The formaldehyde present at the commencement of the incubation period was rapidly assimilated to undetectable thresholds,” the research authors report, “at rates approximately 200 times faster than those documented elsewhere in cloud water.”
This accelerated rate suggests a function beyond mere nutritional uptake, the team posits. It is more likely that these compounds serve a dual purpose, including “detoxification,” as elevated formaldehyde concentrations can prove detrimental to the bacteria.
The encouraging aspect is that these same compounds are also pollutants from a human perspective, implying that this aerial microbial consortium may contribute to atmospheric purification. The precise extent of its real-world ecological benefit awaits further rigorous investigation.
“The possibilities are virtually limitless,” concludes Garcia-Pichel.
The findings of this research have been disseminated in the scientific journal mBio.
