Microbes are just about any living organism that is too small to be seen by the naked eye. Bacteria, viruses, protists, fungi are all microbes. Hardly visible, these tiny beings are almost everywhere. Without a microscope, it is hard to understand the grandeur of this ubiquity. For instance, there are around 10^29 microbes in the oceans alone. 10^29 is 1 followed by 29 zeros—an overwhelming number! Let’s look at something more dwarfed. Consider this: there are 100 times more microbes on and inside us, right now, than there are stars in our galaxy. Even with a conservative estimation, the microbes inside us outnumber our own cells. We are more microbes than we are we! This is how omnipresent they are.
Microbes are often casually regarded as being synonymous with infection. Statistically speaking, ‘making humans sick’ barely makes the cut in their illustrious CV. Of an estimated 1 trillion species of microbes, only 1,400 are known to cause infection in humans. The rest of them are busy producing almost half of the earth’s oxygen or making antibiotics that save millions of lives each year. Bacteria also helped us discover CRISPR Cas9, a gene-editing technology that is said to have the potential to revolutionise mankind. When they’re not being superheroes, microbes also help in making vitamins, hormones, cheese, bread, help with decay and decomposition, trap carbon dioxide, convert N2 for plants, and do many other seemingly trivial jobs that keep the earth alive. Of all the infinite places where microbes are, the most intriguing spot is within ourselves.
It can sometimes seem like we are alone, but our human body is essentially an ecosystem of infinite microbial lives—an entire universe inhabited by trillions of tiny tenants that call ourselves home. These little microbes are collectively called as the human microbiota. These tenants don’t just quietly mooch inside us, but actively change, modify and influence our bodily functions. They cure disease and sometimes cause them. We outsource many important metabolic activities to them and count on them to keep ourselves and their home alive. They are everywhere, on the skin, inside the mouth, in our lungs, guts, colon, uterus, vaginas and almost all other parts of our bodies. They first colonise us when we’re born, and then stay constant for most of our lives.
Microbes are very simple and small as compared to our body cells. This is why they only weigh about 0.2 kg, despite making up more than half of all cells on our body. These tenants are tiny but definitely not lightweights. Humans are known to have about 21,000 genes, whereas the microbes inside us collectively have an upwards of 3 million genes. These genes are together called the human microbiome and produce thousands of metabolites that have a lot of say in how we function.
I think of these microbes as tenants and not as freeloaders because they outsource a lot of metabolic activities for us. In exchange of warmth, food and shelter, these microbes, help us in absorbing and fermenting undigested carbohydrates, train and educate our immune system, synthesise important vitamins and minerals, neutralize toxins, isolate and battle pathogens (umbrella term for microbes that cause illness) and contribute in several other bodily functions that impact many aspects of our well being.
Most of these microbes reside in our intestines. This gut microbiota is sometimes often referred to as the forgotten organ. Lack of diversity and deficit of certain essential microbes in the gut flora is one of the primary reason for the onset of many diseases. Inflammatory bowel disease, psoriatic arthritis and type 1 diabetes in kids have been associated with a lack of diversity in gut microbiota. A 2013 piece of research linked the presence of certain gut bacteria with accelerating the tumour growth in a particular type of intestinal cancers. Similarly, the faecal microbiota of patients with depression was seen to be significantly altered and have less diversity. The presence of certain microbes has been associated with many other diseases like Celiac disease, autism, type 2 diabetes, gastric cancer and allergies. In mouse models, researchers were able to trace back many neurodegenerative diseases like Parkinson’s, Alzheimer’s and mental illnesses like depression and anxiety to altered gut microbes. They also help our kidneys regulate our blood pressure and act as biomarkers for cardiovascular risk.
The microbial exposure in your childhood can influence your adulthood. Kids who grow up near farms or with pets are exposed to a wider variety of microbes and allergens that decrease their likelihood of getting asthma later in life. Bacteria in our guts can influence leptin concentration and subsequently impact our hunger and appetite. Many scientists also believe that our gut microbes can even sway our dietary preferences to suit their growth. This correlation between microbes and obesity is very significant as obesity is the precursor to many disorders. The administration of antibiotics (chemicals that kill microbes, both good and bad) early in infancy could lead to obesity later.
Our primary contact with microbes is established when we pass through the vaginal canal. Babies born through Cesarean section who don’t have that contact are known to be more obese and have weaker immunity as compared to those delivered vaginally. In a very interesting experiment, when germ-free mice received faecal microbes from obese humans, they ended up gaining more weight than the those who got microbes from lean ones.
The idea of “gut feeling” seems a little more plausible as researchers were able to demonstrate that the microbes in our guts can control our mood. In animal studies, the scientist was able to demonstrate that the “gut-brain axis” is controlled by microbes through several mechanisms like releasing neurotransmitters and stimulating the vagus nerve that runs between the brain and the abdomen. This is especially interesting because the microbes that we barely knew were inside us, have shown to control important aspects of our lives like anxiety, stress, and depression. We have now started to realise the significance of harmony in this intricate relationship that we share with our tiny tenants.
The type of tenants that we harbour inside us depend on many factors like stress, sleep, exercise, residence, ethnicity, genetics, drugs, pets, and many other immeasurable actions. Use of antibiotics in early infancy which unsympathetically kills a large spectrum of microbes is linked to obesity later in life. Artificial sweeteners which are generally considered to be safe are shown to decrease bacterial diversity. Until recently, we never really calculated the influence of our microbes while decrypting the aetiology of diseases. Now that we begin to rediscover these new connections, it will be important to consider our tiny tenants in all our equations. They have the potential to not just cause diseases, but also help with diagnosis and cure.
Fecal transplant—the transfer of clinically treated poop, or the gut microbe, from a healthy donor to a sick recipient—can cure a C. difficile infection. It’s also rapidly gaining status as the standard of care for a certain type of diarrhoea. This idea of transferring healthy microbes is now being considered for disorders like obesity, Crohn’s disease, ulcerative colitis and others. Bacterial transplant for eczema showed remarkable success in a recent trial. In 2015, researchers were able to wield certain gut microbes to decrease cholesterol levels in mice. They are now researching further to mimic the same in humans and decrease cardiovascular risk. Intestinal microbes are shown to influence the efficacy of many cancer drugs, employing immigrant microbes to fight the rebellion in our own cells seems to be a promising frontier in cancer care.
Outside the body, gut microbes are being used to dissolve the sugars that give us different blood groups a universal blood for blood transfusions. The monetary potential of these bacteria mediated therapies has to lead to the sprouting of many startups that swear by the power of human microbiome. These startups offer everything, ranging from mapping your microbiome to offering transplants. The research behind most of these startups is still rudimentary but they likely to go mainstream in the coming years. This newfound knowledge might tempt you to lend more of your tummy real estate to these tiny tenants through probiotics, but it is not really a good idea, as recent research found probiotics to be essentially useless for most of us.
Microbes have ruled the world long before we came into existence and are likely to stay here long after we are gone. We evolved from them and now through shared adversaries, we evolve with them. There is this entire obliviated civilisation inside of us that we can’t see, hear or feel. They bank on us to stay alive, and we bank on them. In the clamour and fanfare of life, it is easy to miss out these tiny tenants. So the next time you feel a little deserted and alone, remember that there is inside you a splendid universe of microbes.