Air transportates disease-causing organisms over vast distances.
Airborne microorganisms like bacteria and fungi, including some potentially harmful to humans, can traverse significant distances with some assistance. A group of researchers from Spain discovered this in a study, revealing that these microbes protect themselves from UV radiation at high altitudes by employing a particular strategy.
Wind can carry microorganisms attached to tiny particles up to 2,000 kilometers. This discovery was made through measurements during flights over Japan and on the ground, along with subsequent analyses. These microorganisms include bacteria and fungi, many of which are also known as disease-causing agents in humans, animals, and plants.
The study suggests that these microbes may also carry genes for antibiotic resistance, thereby facilitating the quick spread of antibiotic resistance. Research led by Xavier Rodo from Barcelona Institute for Global Health (ISGlobal) was published in "Proceedings of the National Academy of Sciences" (PNAS).
"Journey through intense wind tunnels"
Rodo stated in a statement from his institute that their study was distinctive due to ten tropospheric flights conducted to analyze the microbial diversity at high altitudes, while most studies have been conducted just a few meters above the ground or ocean.
The researchers conducted the flights in February and April 2014 at an altitude of one to three kilometers. They observed that a high-pressure system over Siberia caused air from northeastern China to rise, which, coupled with a low-pressure system over Japan, caused this air to sink towards the Earth's surface thousands of kilometers away. Rodo explained that the microbes traveled through intense wind tunnels in the troposphere.
Risky portion for human health
The research team identified bacteria from 305 different genera and microfungi from 266 genera. They also investigated the chemical composition of the aerosols to which the microorganisms were attached. Substances such as zinc sulfate and potassium, commonly used in fertilizers, indicated that the tiny particles originated from agriculture, which is intensively practiced in northeastern China.
About 35 percent of the bacterial species and 39 percent of the fungal species detected by the researchers in the high atmosphere on the aerosols could pose a risk to human health. Most of them are opportunistic pathogens, meaning they are harmless to people with a healthy immune system, but can cause diseases in immunocompromised individuals.
This includes Escherichia coli, a bacterium that typically resides in the human gut. However, they also found two strains of Bacillus cereus, which can cause food poisoning, stomach and intestinal inflammation, brain inflammation, and more.
Highly resistant to antibiotics
In the case of Bacillus cereus, the researchers found through laboratory tests that the strains were highly resistant to antibiotics like penicillin, ampicillin, and ceftriaxone. They also discovered genes in other bacterial species and strains that enabled resistance to various antibiotics. Among them was a strain of Micrococcus luteus that was resistant to several antibiotics, contradicting previous knowledge.
"Our results suggest that antimicrobial resistances could spread over long distances via this previously unknown route," said Sofya Pozdniakova from ISGlobal, co-first author of the study.
Exposure to high doses of cosmic radiation
While individual studies have shown the transport of microorganisms over long distances in the atmosphere, scientists generally assumed that bacteria and fungi would not survive the high dose of cosmic radiation at high altitudes.
The study indicates that biofilms, produced by microorganisms through extracellular polymeric substances, could protect them, especially from solar ultraviolet radiation and dehydration. This ability of microorganisms to withstand harsh conditions in the upper atmosphere with the help of a biofilm was confirmed by the study.
"While our study does not necessarily suggest a causal link between the presence of known human pathogens in bioaerosols and health impacts, it opens the door for future research in this area," the research team concludes.
Microbes associated with the aerosols, including bacteria and fungi, showed resistance to antibiotics such as penicillin, ampicillin, and ceftriaxone. During their journey through intense wind tunnels in the troposphere, these microbes were protected from potentially harmful UV radiation by forming biofilms.
