Q.Why are the conventional methods not suitable for the assessment of biodiversity of bacteria?

Conventional methods of biodiversity assessment rely on morphological observation and identification of species, which works well for plants and animals where distinct physical features exist. Bacteria, however, present a fundamental challenge: they are microscopic prokaryotes with extremely simple cellular structures that offer very few distinguishing morphological characteristics. A vast number of bacterial species look nearly identical under a microscope, making visual identification unreliable or impossible.

More critically, the majority of bacterial species cannot be cultured in laboratory conditions. Estimates suggest that less than one percent of bacterial species can be grown on artificial media, meaning traditional isolation and culture-based counting methods miss the overwhelming diversity that exists in natural environments. This limitation renders conventional species richness estimation—which depends on observing, counting, and cataloguing individual organisms—fundamentally inadequate for bacteria. …

When ecologists set out to count species in a forest or a coral reef, they rely on what they can see and classify. A bird's plumage, a plant's flower structure, an insect's wing pattern — these visible traits allow us to distinguish one species from another. This morphological approach has served biology well for centuries. But bacteria present a fundamentally different challenge, one that exposes the limits of our conventional toolkit.

The first problem is appearance. Bacteria are microscopically small, and their structural diversity is minimal compared to plants or animals. Under a microscope, most bacteria appear as simple rods, spheres, or spirals. Two bacterial species that are as ecologically different as a tiger and a sparrow may look virtually identical. You cannot tell from shape alone whether a bacterium fixes nitrogen in soil, causes disease in humans, or produces antibiotics. Morphology, the cornerstone of traditional taxonomy, offers almost no help in distinguishing bacterial species.

The second and more serious obstacle is culturability. Conventional methods depend on isolating organisms, growing them in the laboratory, and studying their characteristics. For bacteria, this means streaking samples onto nutrient agar plates and waiting for colonies to grow. But here is the catch: the vast majority of bacterial species — estimates suggest over 99 percent — cannot be cultured using standard laboratory techniques. They may require unknown nutrients, specific symbiotic partners, or environmental conditions we have not yet replicated. This phenomenon, sometimes called "the great plate count anomaly," means that when scientists plate a soil or water sample, the colonies that appear represent only a tiny, unrepresentative fraction of the microbial community actually present.

Ask what conventional methods require to work: distinguishable shapes and lab-culturability. Both fail for most bacteria, which is why molec …