Mindless talks(Third of three parts)

On speaking terms

It is now well established that Vibrio fischeri excretes AHLs as chemical signals to communicate; Pseudomonas aeruginosa uses both AHLs and the siderophore pyoverdine, and other bacteria actually use peptides or short proteins. These are just the classic examples of chemical signals, but in the myriads of groups of microorganisms that exist, each group uses a specific kind of chemical signal, meaning each group has its own language. Some of these discovered so far are named ComX, SapB, Nod factor, A-factor, etc. So like humans, microbes have different languages like Swedish, Bahasa, Mandarin, Spanish, etc. But like English, they also have a universal language. Scientists termed this chemical signal autoinducer-2 or AI-2 which is found to be widespread in the microbial world facilitating interspecies communication. Messages are also exchanged between two very different groups of organisms. Plants that harbor bacteria in their roots excrete a chemical signal that triggers the expression via quorum sensing by the bacteria of molecules beneficial to the plant and vice-versa.

There are also situations when neighboring microorganisms are not in speaking terms. In cases of competition for available nutrients, a group of bacteria may use their chemical signals to destroy the quorum sensing system of other groups of bacteria in the vicinity. Such deadly messages are used also by the pathogenic Pseudomonas aeruginosa.

Announcing the good news

What got scientists so excited these days about quorum sensing? The alarming emergence of numerous virulent bacteria which are resistant to many antibiotics has set them for many years scrambling for a solution. Numerous bacteria can actually counter attack of antibiotics by producing antibiotic-degrading enzymes. This defense system works like launching patriot missiles to intercept scuds! But scientists have once again come up with an ingenious scheme: if you can’t kill them, silence them!

Scientists are now developing new kinds of warheads in the form of vaccines which will specifically target no other than the autoinducers which trigger quorum sensing, hence blocking the expression of toxins and the formation of biofilms. As a result, the resistant bacteria don’t die but they lose their virulence. It’s like disarming or destroying the enemy arsenals instead of capturing and shooting down all the enemies. This scheme was established by studying the methicillin-resistant Staphylococcus aureus (MRSA) which causes skin disease.

This strategy has also spawned tremendous application in agriculture. Plant pathogens using quorum sensing to colonize grapevines in the wine industry, and in potatoes, onions and other crops are now targeted. Other farm products like poultry, ground beef, smoked salmon, to name a few, are spared from spoilage by knocking down quorum sensing. Inversely, in a very, very important application, quorum sensing is not inhibited but used to enhance the formation of biofilms of bacteria which are capable of degrading environmental toxins and pollutants. These bacteria are seeded in sewage treatment plants and industrial wastewaters.

Walk the talk

The world of microorganisms is indeed a challenging and promising frontier. Quorum sensing is just an eavesdrop of the infinite resounding discoveries that await us. The microbial world not only offers vast potentials for the improvement of the environment and the advancement of biotechnological and biomedical industries, but recently, believe it or not, more and more scientists in the natural sciences are closely working with sociologists to study human behavior and society making use of quorum sensing and other traits of microbial communities as models.

Like in a national election, cooperative behavior is at the heart of such an important event. Democracy is like the

bioluminescence or the light a nation must collectively express. Sincere public servants and competent leaders are the autoinducers of this important expression. Though a single vote counts, it should be strengthened by the majority vote, from a quorum nationwide. This is why military juntas or coups d’etat are unspeakable aberrations in a supposedly democratic, free and cooperative society.

Indeed, as brainless as they are, we brainy humans who constantly struggle in a vain, self-success and egocentric culture can learn so much from the primitive bacteria. There are endless talks on unity and progress but are we measuring up? To achieve and maintain true progress, cooperation is needed. We have shown to the world before that there is always strength in numbers. But always remember, that the powerful essence of cooperation actually starts with no other than with you.

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Dr. Ronie J. Calugay obtained his Ph.D. in Life Sciences and Biotechnology at the Department of Biotechnology, Tokyo University of Agriculture and Technology where he studied iron-shuttling molecules called siderophores produced by magnet-producing bacteria. He finished his MS in Microbiology at the University of the Philippines, Diliman. E-mail him at [email protected].