After the Eclipse Is Over: Microbes and, Uh, Sun-Powered Laundry Drying

Bacterial life on the 3rd rock from the sun.

Imagine for a moment that the sun was the size of a yoga ball.

The moon would then be roughly the same diameter as the tiny sphere on the end of a sewing pin.

In spite of this 400:1 size differential, for a few minutes yesterday, our friendly local star and our one and only moon appeared to be precisely the same size in the sky, allowing one to cover the other almost exactly.

Here in San Francisco, those who ventured onto the roof of our building were rewarded with – rather than the total solar eclipse that was experienced in a band across the United States – a banana in the sky.

But it was still fun to see people with colanders and home-made pinhole cameras, enjoying a phenomenon that was last exclusively experienced in the land now known as the US more than 700 years ago, on June 13th, 1257.

A Wednesday, if you wondered.

If you were fortunate enough to have been anywhere within the zone of totality, you may have experienced a kind of slightly spooky darkness and stillness, when birds and insects went quiet.

Larger, two-legged organisms, on the other hand, went “Ooh.”



And, “May I borrow your colander?”

However, humans aside, this temporary cessation of activity by living critters got us thinking about those much tinier organisms that fill most of our waking hours here at uBiome.

What, if any, are the connections between bacteria and sunlight?

Allow us to illuminate you.

In the days before dryers (on that Wednesday in 1257, for example) folk wisdom had it that hanging your wet laundry to dry in the sun a) got the job done more quickly, and b) helped to kill off “germs” – the microorganisms we now know more graciously as bacteria.

Unfortunately, while there’s no doubting the rapid laundry-drying effects of sunlight, it’s sadly true that after its journey through the Earth’s ozone layer, ultraviolet (UV) light from the sun is nowhere near powerful enough to kill bacteria.

Think about it: surfaces in nature are continually exposed to the sun, and they’re also permanently covered in bacteria.

So you’d better rely on your laundry detergent to rid your laundry of any microbial nasties it may harbor.

This is not to say that UV doesn’t have its applications in disinfection.

At much higher intensities, it’s widely used in industry to treat drinking and wastewater, for example – and does so by damaging the DNA of bacterial cells, generally killing them.

It’s a process known, perhaps not so snappily, as ultraviolet germicidal irradiation, and is based on methods first established by the Victorian scientists Arthur Downes and Thomas Blunt in 1878.

Their work laid the foundations for Niels Finsen, a Dane, who was awarded the 1903 Nobel Prize in Medicine, for his use of UV radiation against Lupus vulgaris (tuberculosis of the skin) caused by the microorganism Mycobacterium tuberculosis.

Finsen is sufficiently renowned to warrant a statue in Copenhagen, depicting a naked man and two women (presumably representing neither Finsen himself nor [cough] females of his acquaintance) reaching to the sun, symbolizing Finsen’s principal scientific theory that sunlight can have healing properties.

As a side-note, and along the lines of Decca Records turning down The Beatles by snarkily telling them that “guitar groups are on the way out,” Finsen’s school principal said of the future Nobel laureate, that he was “a boy of good heart but low skills and energy.”

So far, we’ve seen that UV light can lead to the demise of bacteria, but then there are those other types of bacteria that positively relish a bit of the old UV.

Cyanobacteria, for example, which are probably the oldest organisms in the world, are able to perform the biological equivalent of simultaneously patting their heads while rubbing their bellies.

They can, you see, engage in oxygenic photosynthesis (using light energy to produce oxygen and carbohydrates from water and carbon dioxide) while also indulging in cellular respiration (getting energy from a molecule such as sugar, a process more commonly known as fermentation).

In fact, Cyanobacteria’s versatile powers have led researchers at Binghamton University in New York to create an experimental bacteria-powered solar panel.

Although the idea has exciting potential, you could say that it’s early days for this technology.

At the moment, an array of nine biological solar (bio-solar) cells can generate a modest 5.6 microwatts.

To put this in perspective, to produce the approximately 200 watts generated by one single traditional solar panel in strong sunlight, we’d need to put bio-solar panels on the roofs of…

5.4 million homes.

That’s substantially more households than there are in the entire state of Pennsylvania.

However, before we dismiss the electricity-generating potential of Cyanobacteria entirely, we might do well to recall the words of those Decca Records executives, who also claimed, “The Beatles have no future in show business.”

Here comes the sun.

More reading

Can the sun kill germs?

Clean energy generated using bacteria-powered solar panel

Co-existence of photosynthetic and respiratory activities in cyanobacterial thylakoid membranes

Effect of Natural Sunlight on Bacterial Activity and Differential Sensitivity of Natural Bacterioplankton Groups in Northwestern Mediterranean Coastal Waters

How does ultraviolet light kill cells?

Niels Ryberg Finsen

Photosynthesis and Respiration in Cyanobacteria


The Solar Eclipse Coincidence

Ultraviolet germicidal irradiation