Human establishment over Mother Earth is on its verge of becoming a success day by day. But the thought of co-habitants have started to dwell in the minds of environmentalists as it is known that an ecosystem is healthy and complete only if all the species coexist. Mutualism, predation and parasitism play an important role for the existence of the ecosystem. But, the influence of human race on the environment is to such great extent that it is given a new name-“The Anthropocene-the age of man”. When we discuss about the conservation of nature and impact of the superior species, the tiny microorganisms are generally ignored. But, how much do we know of how they evolve with us? How much do we know about their strengths and intelligence? Those miniscule organisms are actually prudent and may even take over the earth very soon! They have co evolved with us in every stage of life- from the agricultural era to the industrial revolution.
It is a well known fact that there are 10 times more microbes than our cells! Stage after stage when we evolved, our microbial friends would have definitely grown with us. How do we acquire the first microbes? The question that now arises is about the composition of the community at birth. Exposure to maternal microbes and environmental microbes influence the first microbes in our body. Now how does it relate with our evolution? The delivery mode. Until 1950’s C section was uncommon and that created a distinction between the two periods in the microbial community. After that the microbial succession was based on the feed, be it bottle feeding or breast feeding or the exposure of antibiotics. The food style controls too. It has been seen that when there was a transition from the hunter-gatherer lifestyle to the cereal consumption lifestyle our microbial community have changed according to the data obtained from fossiled dental calculus. Then we moved on to the technological era eating huge amount of processed foods. That was once again a transition for our tiny people. So depending on your diet, be it the high protein and animal fat or high fibre content, microbial community vary and cluster accordingly. The gut microbiome can be very clearly distinguished from the herbivores and the carnivore-omnivore species.
Do you know that we are marching on to the post antibiotic era? Yes, our fellow microbes are slowly developing resistance to the antibiotics we have discovered against them. Different mechanisms for their destruction are under major research. There were no antibiotic resistance genes in mobile DNA elements such as plasmids before the World War II which can be understood logically. Genes conferring from different origins were assembled together due to selection pressure from antibiotics, disinfectants and heavy metals. These genes are xenogenetic that is they are direct results of human activity. There are other problems such as the release of unused antibiotics in low concentrations that prevail in the environment. They cause the non- target bacteria and promote new resistance among the population.
The biogeochemical cycle is carried on actively by microbes. Domesticating variety of animals and plants has affected the symbionts and thus the key organisms involved in the carbon nitrogen cycle are altered. The best example can be the increase in the rate of methane production from the pre and post agricultural era. There has been a threefold increase making to the highest. Flooded rice cultivation and ruminant farming have increased methanogen production, which obviously increases the methane content in the atmosphere linking to climatic factors! The sauropod dinosaurs in the Mesozoic era were herbivores, and they produced methane which increased the temperature. So, microbial activity in large herbivores contributes significantly to climatic changes. Similarly, we cultivate more legumes in recent days and increase the nitrogen content in the atmosphere. There was an increase in the atmospheric nitrous oxide content owing to livestock expansion and usage of industrially fixed nitrogen as fertilizer. What harm can it do? Increased nitrogen content declines the biomass of mycorhizzal fungi, nitrogen runoff cause algal blooms that produce toxins and may also lead to eutrophication.
Anthropogenic activities have increased carbon-di-oxide content leading to the hot global warming. How does this affect the invisible community of microbes? Increase in carbon-di-oxide effects plant growth. That in turn increases secretions from roots, which affects the soil bacteria and fungi. Soil warming affects the microbial composition and the distribution in the soil. They would have to migrate to higher latitudes, changing disease vector distribution and may result in release of water borne diseases.
Migration of microbes? Is that even possible? This leads us to think about yet another view. Only human activities potentially help in their transfer. The first transport occurred when humans dispersed from Africa, carrying parasites with them. The human specific parasite movement can actually help in predicting the pattern of human migration too. Then came the settlement of man from the nomadic life. That led to self sustaining infectious diseases. We are also now in close contact with animals and that could imply transfer of pathogens from animal to human host. Mumps, measles, small pox and diphtheria came about in this manner. Permanently settling in a civilisation gave rise to new vectors like the rodents. Long distance dispersal of disease came to existence as the maritime transport began during the age of exploration which hastened with the mechanized transport, rose to a great extent with the mass transit systems.
We can thus evidently see how the microbes evolve parallel with human civilisations. There are lot of instances that show how the microbial evolution affect us indirectly which are hidden beneath. They may not be reflected in fossil records or may have no direct evidence in the biology of these transitions. It is a new thought to ponder upon. Looking on a new perspective we may realise that the general kinds of phenomena we see today are those which occurred during transitions in previous eras and our little shrewd microbes are indirectly the causatives!