Dirtier than a toilet

Why are there so many bacteria in kitchen sponges

Kirill Stasevich, Science and Life (nkj.ru )

A dish washing sponge is one of the dirtiest items in the house: a few years ago, Scientific Reports published an article saying that in one cubic centimeter of a dish sponge, you can count more than 5x10 ¹⁰ bacterial cells — seven times the number of all people on Earth. (For comparison, beneficial bacteria in fermented milk products should be a thousand times less – VM.)

Obviously, the sponges are so dirty, because a lot of nutrients remain on them, even if we wash the dishes with special means. But it's not just the nutrients, but also the fact that many different bacteria can peacefully get along with each other in a sponge. The relationship between bacteria is quite complex; the same bacterium can be friends with some and dislike others, respectively, it will grow and multiply actively or not very actively, depending on who it gets to be neighbors. But the neighborhood can also be structured in different ways. Staff Duke University studied the interaction of several dozen strains of E. coli, which were all crowded into a die with a nutrient medium and cells of different sizes. The die was divided either into six large cells, or into smaller cells, or even smaller, etc., until there were more than one and a half thousand cells.

In an article in Nature Chemical Biology (Wu et al., Modulation of microbial community dynamics by spatial partitioning), researchers write that both large cells and small ones eventually had a couple of strains left. On too large a "territory" and on too small, it was difficult to maintain all the diversity of ecological connections, and most strains left the scene. But in medium-sized cells, the bacterial diversity was quite high.

Different strains of bacteria glow with different colors. Photo from the press release of The Surprising Structural Reason Your Kitchen Sponge is Disgusting.

Something similar happens in a porous kitchen sponge, which is a convenient structured reservoir in which different types of bacteria can thrive side by side — in this "dormitory" with "rooms" of different sizes, they do not interfere with each other. Experiments have shown that it is possible to achieve such microbial diversity in a sponge, which no other methods of laboratory cultivation of bacteria allow. By the way, bacteria find the same convenient structure in the soil, with its micro—cavities, micro-cracks, etc. - indeed, it is difficult to find another substrate where bacteria would be as at ease as in the soil.

For researchers who deal specifically with the ecological aspects of bacterial life, it makes sense to pay attention to sponges: for example, various communities of soil microbes can be grown in them, in which they will live almost as in nature. But it is quite possible that the "spongy" cultivation of bacteria will also be useful in industry, in those industries where it is necessary to manipulate several types of bacteria.

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