Preface

Acidophiles, as an important class of extremophiles, have attracted attention for their scientific significance and application value. Acidophiles are microorganisms that thrive in acidic conditions and can be found in Bacteria, Archaea, and Eukarya. Acidophiles can be identified in both terrestrial and marine environments, including acid mine drainage (AMD) from metal and coal mines, iron-sulfur mineral mines, hot springs, and sediments. In these acidic ecosystems, acidophiles could participate in the element cycles (sulfur, iron, etc.) and promote the generation of the acid environment and formation of the acid micro-ecosystem. Acidophiles can also be found in the human body. Research on acidophiles can help us understand the diversity, adaptation, and functions of these microorganisms and contribute to the development and application of new biotechnologies for resolving problems of resource exploitation, pollution, and human disease. This book provides breakthroughs and insights into the research on acidophiles. Chapter 1 introduces acidophiles and their important physiological characteristics and industrial applications. Chapter 2 discusses the two-component signal systems in the regulation of sulfur and ferrous iron oxidation in acidophilic bacteria. Chapter 3 focuses on the acid-resistance adaptation mechanisms in acidophiles. Chapter 4 introduces the quorum sensing system (QS)-mediated communication mode in chemoautotrophic acidophilic bacteria and the function of QS in the regulation of bacterial sulfur oxidation, ferrous iron oxidation, and mineral oxidation. Chapter 5 discusses the application of QS and QS signals on bioleaching industries. The final chapter deals with acidophiles in human health, including the immunomodulatory potential of *Lactobacillus acidophilus* and its potential role as a therapeutic for the management of inflammation-induced bone disorders.

> **Jianqiang Lin, Linxu Chen and Jianqun Lin** State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China

## **Chapter 1**
