As the oldest living organisms on Earth, bacteria have some tricks up their sleeves. How can a single celled organism with no organelles and just one DNA strand accomplish anything tricky? They do sleights of hand with light, responding to it by converting different wavelengths into chemical signals.
A new study illuminated (pun intended) the signaling role of bacterial membranes, which act kind of like nerve cells. Bacteria don’t have nervous systems, but changes in electrical potentials across their cell membranes help bacteria do things like mechanically sense their environments; share nutrients between colonies; or form biofilms with other bacterial species.
“It is intriguing to analogously consider these signaling and circuits as forming a ‘bacterial brain’ that regulates metabolism and adaptation/responsivity to external stimulus,” explain the study authors. They found a chemical switch that induced membrane hyperpolarization in the bacteria Bacteria subtilis when exposed to light.
See the flashy results HERE.
If light-responsive potentials weren’t enough, soil bacteria create a natural electric grid. In soils without oxygen, like the seabed, bacteria form tiny conductive nanowires. Says Nikhil Malvankar, author of a 2021 study that uncovered the mechanism, “The ground beneath our feet, the entire globe, is electrically wired.” A pair of proteins in the buried bacteria pump out the nanowires, as shown HERE.
Now, a recent study shows that light enhances the electrical conductivity of these nanowires. The researchers exposed bacteria to light and found an increase of up to 100-fold in electric current, adding to the tantalizing possibility of harnessing bacteria to generate electricity. Says Malvankar, "The dramatic current increases in nanowires exposed to light show a stable and robust photocurrent that persists for hours.”
Too much light of the wrong kind, however, can be fatal for bacteria; thus, the increasing use of blue light therapy to fight infections such as MRSA. As more antibiotic-resistant bacteria evolve, microbiologists are in a frantic search for additional weapons against them. When certain bacteria are exposed to blue light in the 400-470 nm wavelengths, their photoreceptors sense the light and trigger the fatal production of toxic reactive oxygen.
A new study probed the effects of blue light on the particularly pesky bacteria — Pseudomonas aeruginosa — that colonizes wounds and resists antibiotics. By experimenting with different light intensities and exposure times, the researchers found that death by illumination happened with high intensity exposure over two hours.
In their bag of tricks, some bacteria produce light. In a phenomenon called “quorum sensing,” bacteria talk with each other using chemical signals that coordinate light-making. For example, the marine Vibrio fischeri bacteria that live inside squids coordinate a fluorescence every night, which helps squids hunt without casting a shadow. And in the daytime, a squid ejects its excess bacteria and makes way for a fresh crop.
So, although single-celled, bacteria have sophisticated tricks up their sleeve for a nuanced relationship with light. And their real superpower is in the teamwork.