Microorganisms which can survive extreme conditions are called extremophiles. They have a hard covering sheath on their surface and are capable of forming endospores. These are very hard covered resistant spores which enable the microorganisms to tide over harsh conditions. 

How do microorganisms survive under adverse conditions?

Microorganisms are highly adaptable and can survive under adverse conditions through various mechanisms. These mechanisms allow them to endure extreme temperatures, pH levels, desiccation, radiation, and other unfavorable environmental factors. Below are some ways in which microorganisms can survive under adverse conditions:

1. Dormancy and Spore Formation:
- Many microorganisms can enter a dormant state when conditions become unfavorable. During dormancy, their metabolic activity decreases significantly, allowing them to conserve energy and survive for extended periods.
- Some microorganisms, such as bacteria and fungi, can form spores as a survival strategy. Spores are highly resistant structures that protect the genetic material of the microorganism. They can withstand harsh conditions until favorable conditions return, allowing the spore to germinate and resume active growth.

2. Metabolic Adaptations:
- Microorganisms can adjust their metabolic pathways to cope with adverse conditions. For example, some bacteria can switch to anaerobic respiration when oxygen levels are low, ensuring their survival even in oxygen-depleted environments.
- Certain microorganisms can also utilize alternative energy sources when their primary energy sources are limited or absent. This metabolic flexibility enables them to sustain their growth and survival under adverse conditions.

3. Protective Structures:
- Microorganisms may produce protective structures such as biofilms, capsules, or extracellular matrices to shield themselves from harsh environments. Biofilms are communities of microorganisms that live together and secrete a protective matrix, which provides physical protection and enhances resistance to environmental stressors.
- Capsules are slimy layers surrounding some microorganisms, serving as a protective barrier against dehydration, immune responses, and antimicrobial agents. These structures contribute to the survival of microorganisms under adverse conditions.

4. DNA Repair Mechanisms:
- Microorganisms possess sophisticated DNA repair mechanisms that help them survive DNA damage caused by environmental stressors such as radiation or toxic chemicals. These repair mechanisms can correct mutations and restore damaged DNA, ensuring the survival and genetic integrity of the microorganisms.

5. Horizontal Gene Transfer:
- Microorganisms can exchange genetic material through horizontal gene transfer, allowing them to acquire beneficial traits from other microorganisms in their environment. This mechanism enhances their ability to adapt and survive under adverse conditions by gaining new genes that confer resistance or tolerance to stressors.

In conclusion, microorganisms employ various strategies to survive under adverse conditions. These mechanisms include entering dormancy, forming spores, adapting metabolic pathways, producing protective structures, utilizing DNA repair mechanisms, and engaging in horizontal gene transfer. These adaptations enable microorganisms to endure and thrive in diverse and challenging environments.

Under unfavorable conditions of temperature and water, they generally from a hard and tough covering called cyst . When favorable conditions come, they emerge from their shell, multiply and go through their life cycle