A tribute to our life-long intimate companions: The microbes

It’s quite humbling to know that humans account for only 0.01 per cent of the total biomass available on our planet. Microbes, on the other hand, represent more than 17 per cent of the total life.

It’s not only that microbes have lived longer (approximately 3.7 billion years) than the humans, which can be traced back to roughly 7,50,000 years, at max, but are critical to support the earth’s ecosystem. It will not be an exaggeration if it is stated that evolution and sustenance of life, we see on earth today, may not have been possible without the help of these tiny creatures.

Microbes are often blamed for causing infections and diseases, but the fact is that only a very small number (< 1500) is known to cause illness. Rest, the trillions of species, existing on earth are either harmless or supportive to the existence of life. If we think about the recycling of waste or nutrients; fixation of atmospheric nitrogen by plants is critical for their growth and world’s food supply needs, for example, creation of bread, yogurt or cheese by fermentation or producing metabolites such as Penicillin and Erythromycin, useful as life-saving drugs, the credit for all this goes to the microorganisms living with or around us.

The gut microbiome: Our lifetime humdums

The gut microbiome is an important contribution to our gut eco-system. The large surface area of the gut not only plays an important role in absorbing the ingested nutrients and excreting waste product of digestion, but also by hosting > 95 per cent of the total human microbiome, which counts to > 100 trillion in numbers. If we go in details, the human microbiome is constituted of > 4,000 different species of bacteria, fungi and viruses, and we know a very little about it. The relationship between gut and the microbiome, is largely symbiotic in nature, and these tiny friends repay their debt for being provided with food and home, by supplying with substances (metabolites) which, in turn, play important role by helping their hosts in maintaining good mental and physical health.

Some microbes are important for digesting dietary fiber into Short-Chain Fatty Acid (SCFAs), such as butyric acid and anandamide. The digestion of resistant starch, for example, requires synergy between different bacteria, right from cleaving the bonds linking glucose chain to processing its digestion. Microbes not only participate in regulating biochemistry of the host, but also play an important role in synthesising Vitamin B and K, along with metabolising bile acids, sterols and xenobiotics.

Against the proclamation made by Pasteur that ‘animals lacking bacteria would die,’ microbes were considered to be harmful to the human health and cause for chronic inflammation in the various parts of the body, including the gastro-epithelial cells that protect our gut, till the beginning of 21st century.

Today, scientists, on the contrary, believe that gut microbes play an important role in keeping the human health in shape and even a large number of diseases such as autism, epilepsy, depression, cancers, metabolic syndrome and even neuro-degenerative diseases, such as Alzheimer’s and Parkinson’s are linked to the disordered microbiome of the affected people. The basis for this inference is the research finding that the germs-free mice are not only susceptible to stress, but return to normal when fed with Lacticaseibacillus rhamnosus JB-1, a prebiotic, known to influence the immune system. These studies also provide an evidence for a possible link between gut microbiome and brain and also a support to the belief that the quality of the microbiome is important to keep us in good mental health.

We are what we eat. To the best of our understanding, the microbiome of each individual is unique, and does not differ drastically over the total life span, unless the person has suffered with some chronic or life-limiting disabilities. Drastic changes in diet have also been found to affect the microbiome of a person.

Babies are born with a stable microbiome, as mentioned above, but with few gut bacteria, and as they start living on milk, their gut become colonised with Bifidobacteria (Bifids). Breast-fed babies usually are colonised with B. infantis, which helps strengthening baby’s immune system to respond to the infections in the later life. A paper published in Nature, 2019 dealing with ‘Baby Biome’ confirms that ‘21st Century life is bad for infants microbiome.’

As children grow, their gut microbes also change depending on the type of food they take. A healthy adult living on diverse diet are likely to maintain their microbiome with younger characteristics than the one who sticks to a particular food habit with limited options, in the latter part of their lives. A healthy microbiome plays an important role in maintaining good health, however, if disturbed for whatever reasons, is being suggested to cause wide variety of problems, beyond metabolic disorders related to digestive system, as discussed above.

Altering diet appears to provide a practical approach for improving the gut microbiome. Interestingly, the consumption of fermented food, such as yogurt, sauerkraut, etc (probiotics) have been found to create a rich diversity as reported in the journal Cell. The findings suggest that consumption of fermented food not only resulted in the dip in the activation status of four distinct immune cells, but also in the reduction in the levels of 19 inflammatory proteins in the circulation including interleukin-6, a cytokine associated with arthritis and chronic stress.

As expected, the use of the ‘probiotics’ with ‘prebiotics’ (the food supplements that support the growth of healthy bacteria) has also been found to add richness to the microbiome. In a study where Lactobacillus plantarum (a probiotic) was fed with fructooligosaccharides (a prebiotic), it  helped in reducing the incidences of sepsis, lower respiratory tract infections and even deaths in young infants in poor rural population. This supports the hypothesis that diet makes significant difference to the quality of the microbiome and also improving and maintaining good human health.

Simply a four-week intake of yogurt with probiotics modulating brain regions that control the central processing of emotions and sensation and concomitant depletion of Coprococcus & Dialister, known to have correlation with human health in individuals suffering with depression gives further evidence about the link between the health of gut microbes and humans. The reduced levels of cortisol, the stress hormone, production when healthy volunteers were fed with galactosaccharide, a prebiotic known to provide sustenance to the gut bacteria, Lactiobacillus and Bifidobacteria, similar to the one observed when the subjects were treated with anti-depressants or anti-anxiety drugs, further prove that gut microbes have direct access to the brain and do influence the brain chemistry.

The way forward

Since Fecal Microbial Trials (FMT) are showing promise in treating various diseases, such as Parkinson’s, Alzheimer’s, cancers, cognition, metabolic syndrome and recurrent infections caused by Clostridium difficle (rCDi), it gives a hope that manipulation of gut microbes may one day provide us with a clinically proven healthy solution for treating/managing many diseases and also maintaining good health without medical interventions. However, one thing that clearly emerges out from the understanding developed so far is that diet plays a critical role in maintaining a rich microbiome as well as good human health, which is in congruence with our ancient wisdom available with us for more than 2,500 years. Bhagvad Gita, for example, classifies all foods into three categories namely Sattvik, Rajasik and Tamasik based on their characteristics and qualities and explicitly mentions that it has direct effect on our mind as well as body, and also reflects our personalities. Sattvik food is nutritious, easy to digest and helps in enhancing longevity, intellect, health and happiness. For those curious to know the origin, Sattvik, is taken from Sanskrit word Sattva, which means pure or honest.

It may take time before scientists find the underlying mechanism with which gut microbiome influences human health and translate it into cures, however, does not stop us taking a note of what we eat if we want our close friends to remain friendly and supporting to our good health.