Q.What is the group of bacteria found in both the rumen of cattle and shidge of sewage treatment?

The group of bacteria you are looking for is methanogens. These are anaerobic bacteria that produce methane gas as a metabolic byproduct. They thrive in oxygen-free environments, which is why they are found in both the cattle rumen (where they help digest cellulose) and in the sludge of sewage treatment plants (where they break down organic matter duri …

To understand why methanogens appear in such different settings, we need to look at the common condition they require: anaerobic (oxygen-free) surroundings. The rumen of cattle is a large fermentation chamber where plant material is broken down by microbes in the absence of oxygen. Similarly, the sludge in a sewage treatment plant — especially in the anaerobic digester tank — is a dark, oxygen-depleted zone where organic waste is decomposed. In both places, methanogens play a crucial role in the final stage of decomposition.

Methanogens are not bacteria in the strict biological sense; they belong to the domain Archaea, but NCERT textbooks often refer to them as a group of bacteria for simplicity. They are obligate anaerobes, meaning oxygen is toxic to them. In the cattle rumen, they help digest cellulose by converting the hydrogen and carbon dioxide produced by other microbes into methane. This methane is then belched out by the animal. In sewage treatment, methanogens act in the secondary treatment stage, specifically in the anaerobic sludge digester. Here, they digest the bacterial biomass (the floc) and produce a mixture of gases called biogas, which is rich in methane and can be used as fuel.

A shared-habitat-requirement approach.

Instead of recalling the organism name directly, reason from the environmental condition the two locations have in common:

1. List the defining feature of each habitat: the cattle rumen is a sealed fermentation chamber with no oxygen; the sludge digester of a sewage plant is likewise an oxygen-free compartment where settled organic solids accumulate.
2. Ask which functional group of microbes is defined precisely by needing an oxygen-free environment AND producing methane as its characteristic metabolic end-product -- this points directly to methanogens. …