Write a note on estimates of total number of microbial species.
Answers
centuries, humans have endeavoured to discover and describe the sum of Earth’s biological diversity. Scientists and naturalists have catalogued species from all continents and oceans, from the depths of Earth’s crust to the highest mountains, and from the most remote jungles to our most populated cities. This grand effort sheds light on the forms and behaviours that evolution has made possible, while serving as the foundation for understanding the common descent of life. Until recently, our planet was thought to be inhabited by nearly 10 million species (107). Though no small number, this estimate is based almost solely on species that can be seen with the naked eye.
What about smaller species such as bacteria, archaea, protists and fungi? Collectively, these microbial taxa are the most abundant, widespread and longest-evolving forms of life on the planet. What is their contribution to global biodiversity? When microorganisms are taken into account, recent studies suggest that Earth might be home to a staggering 1 trillion (1012) species. If true, then the grand effort to discover Earth’s biodiversity has only come within a 1,000th of 1 per cent of all species on the planet.
Estimating microbial diversity even in the most ordinary of habitats presents a unique set of challenges. For more than a century, scientists identified microbial species by first culturing them on Petri dishes and then characterising cellular properties, along with aspects of their physiology such as thermal tolerances, the substrates they consume, or the enzymes they produce. Such approaches dramatically underestimate diversity, not only because it is difficult to grow the vast majority of microorganisms, but also because unrelated microbial species can perform similar functions and are unlikely to be distinguished by their appearance