The filamentous appendages called pilli are present only on?

Explanation

Pili are filamentous structures primarily found on gram-negative bacteria. These appendages are crucial for various functions such as adhesion to surfaces, facilitating bacterial conjugation (exchange of genetic material), and sometimes aiding in motility. The cell wall structure of gram-negative bacteria, characterized by a thinner peptidoglycan layer, supports the extension of pili. In contrast, gram-positive bacteria have a thicker peptidoglycan layer that typically prevents pili formation, although they may have other attachment mechanisms. Chemo-synthetic bacteria do not predominantly rely on pili as they are more concerned with chemical energy production processes.