February 23, 2021 | David F. Coppedge

Microbes Travel the Globe

The tiniest of life forms are able to traverse continental distances on wings of the wind.

Birds migrate; some, like the arctic tern, can fly from one pole to the other. Some mammals migrate hundreds of miles a year. Delicate butterflies can fly from one continent to another. Spiders can ride the winds by “ballooning” with strands of web over hundreds of miles. But microbes? They are so small. They have no wings or mechanisms to travel. Some live in water; how could they move long distances? Be very surprised.

Atmospheric transport of North African dust‐bearing supermicron freshwater diatoms to South America (Geophysical Research Letters). This paper tells how tiny diatoms travel long distances in the atmosphere. What the researchers found has “implications for iron transport to the equatorial North Atlantic Ocean.” It’s clear that dust can blow over long distances. Within some of that dust, though, are the remains of dried-up diatoms and living pollen grains.

Atmospheric aerosols from Africa are transported by the trade winds to the western equatorial North Atlantic Ocean every winter and spring and can contain nutrients, such as iron (Fe). In this study, we measured the size and composition of supermicron (diameter (d) > 1 μm) aerosols collected at a site on the northeast coast of South America. Using electron microscopy, we found three distinct Fe‐containing particle types: mineral dust, freshwater diatoms from African paleolakes, and pollen grains; all three particle types extended into the super‐coarse mode (d > 10 μm). Particle asphericity increased with increasing particle size and could explain in part the long‐range transport of super‐coarse particles. Electron mapping of freshwater diatoms also revealed surficial Fe‐rich inclusions. Once deposited in the ocean, the asphericity and light density of freshwater diatom particles likely increases their residence time and therefore, the time for Fe dissolution in the surface ocean compared to dust.

Does this migration of diatoms and pollen grains do any good for the places they fall? Yes!

The equatorial North Atlantic Ocean (NAO) is a nutrient‐limited ecosystem that relies on the deposition of long‐range transported iron (Fe)‐containing aerosols to stimulate primary productivity.

Who would have thought that the north Atlantic gets its nutrients from Africa? It’s astonishing, really. Freshwater diatoms (FDs) make up 38% of the dust particles the scientists examined under the microscope (it’s not clear from the Abstract if any of them were still living). Because diatoms are aspherical, they likely fly better than spherical dust particles. The team thought of this as “a mechanism by which they can be carried great distances aloft.” Not only that, the aspherical shape probably increases the “residence time of FDs in surface waters thereby increasing the time for Fe dissolution and their potential impact on marine biogeochemical cycles.

In this unexpected way, the nutrient-poor waters of the north Atlantic get an annual gift from heaven, coming special delivery via wind from Africa. Diatoms, we have reported (19 June 2014, 27 March 2018, 29 June 2020), make exquisite crystal palaces for themselves that they construct from silica. The gifts from heaven therefore come beautifully wrapped, too.

Assortment of diatoms (Wikimedia Commons)

In a related paper in Nature Scientific Reports, scientists found that a genus of freshwater diatoms that live in soil was not restricted to eastern Europe. Species were found thousands of miles away in central Asia, indicating that these tiny single-celled organisms are truly “cosmopolitan.”

Microbes could pose health, ecosystem risks when rain brings them to Earth (Phys.org). Set aside the pessimistic statement about health and ecosystem risks for a moment and consider the wonder: microbes “hitch rides in clouds and enter soil, lakes, oceans and other environments when it rains, according to a Rutgers co-authored study.” The researchers looked at the contents of clouds in France and found living beings.

They collected cloud water at the summit of puy de Dôme, a mountain in central France, about 4,800 feet above sea level. They also collected rainwater below the mountain at about 2,230 feet above sea level. They detected blue-green (cyanobacteria), green, red and golden algae, as well as diatoms (another form of algae), and they grew green algae in the Chlorellaceae family in a lab.

How far had these living organisms traveled?

Some of the microbes that hitched a ride in clouds may have come from the Atlantic Ocean. Others were likely from other parts of France that clouds passed over. Microbes in rain include those in a cloud and the air below it.

The scientists are only speculating about health risks from these microbes. Actually, when considering that these transport mechanisms have likely been operating since creation, it seems unreasonable to suspect they are all bad.

The airborne organisms could have important impacts on atmospheric processes and the ecosystems they enter after falling to Earth, the study says.

The microbes likely provide condensation seeds for cloud formation, and for the rain that follows. Those are beneficial processes for most ecosystems. The microbes should be considered innocent till proven guilty. The authors acknowledge in their source paper that more study is needed to figure out the impact of these organisms.

Oxygenic photoautotrophic microbes are integral to ecosystem functioning, and some have the potential to affect human health. A better understanding of the diversity and the movements of these aeolian dispersed organisms is needed to understand their ecology, as well as how they could affect ecosystems and human health.

The authors also acknowledge that “the atmosphere carries diverse, viable oxygenic photoautotrophic microbes and acts as a dispersal vector for this microbial guild.” If that has been happening for thousands of years, and many nations enjoy good health, then it’s probably a beneficial process. It’s also amazing that such tiny forms of life, carrying chlorophyll and DNA, can spread their benefits far and wide via clouds.

Source: Dillon et al., “Cyanobacteria and Algae in Clouds and Rain in the Area of puy de Dôme, Central France.” Applied and Environmental Microbiology, 23 Oct 2020. DOI: 10.1128/AEM.01850-20.

See also: “Information Storage in the Clouds,” Evolution News 23 Aug 2017.

One can rightly ask if the biosphere would be as rich without these long-distance transport mechanisms. Another factor should be added to the wind and cloud transport of microbes: the fact that birds, butterflies and spiders carry their own microbiomes with them wherever they go. Large animals are effectively “sprinklers” of microbes across the landscape.

Science has revealed that microbes, bacteria, algae, fungi and pollen grains are ubiquitous. The vast majority of microbes are beneficial. We should consider that the working biosphere, with its long distance transport of nutrients in the wind, is a beneficial, well-functioning system that indicates intelligent design.


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