The examples of bacteria that release gases during metabolism are:

$\to$ Bacteria and fungi carry out the process of fermentation and during

this process, they release carbon dioxide. Fermentation is the process of

converting a complex organic substance into a simpler substance with the

action of bacteria or yeast. Fermentation of sugar produces alcohol with the

release of carbon dioxide and very little energy.

$\to$ The dough used for making idli and dosa gives a puffed appearance.

This is because of the action of bacteria which releases carbon dioxide. This

CO2 released from the dough gets trapped in the dough, thereby giving it a

puffed appearance.