Ion transporters play an important role in maintaining intracellular pH homeostasis and ionic equilibrium. Sodium ion transporters and potassium ion transporters exist widely in halophilic and halotolerant microorganisms, and their function of retaining potassium and excreting sodium is one of the two major strategies for microbial tolerance to salt stress. In recent years, new sodium and potassium ion transporters, such as RDD, UPF0118, DUF, and KimA, have been discovered in halophilic and halotolerant microorganisms. The transporters of other metal ions, such as Fe3+ and Mg2+, have been proved to play a role in microbial osmoregulation by participating in the synthesis of intracellular compatible solutes. This paper reviews the ion transporters associated with salt stress tolerance in halophilic and halotolerant microorganisms, analyzes their molecular structures and working mechanisms, and prospects for their applications in agriculture. Discovering new ion transporters, revealing the structures and mechanisms of ion transporters associated with salt stress tolerance, and analyzing the synergistic effect of coexisting transporter systems and their regulation mechanisms will deepen the understanding of the regulatory mechanisms of salt stress tolerance of halophilic and halotolerant microorganisms and provide new ideas for the improvement of crops in saline-alkali land.
Citation
MA Xin, MA Xiangrong, ZHU Derui, LI Yongzhen, XING Jiangwa. Advances in ion transporters associated with tolerance of halophilic and halotolerant microorganisms to salt stress. [J]. Acta Microbiologica Sinica, 2024, 64(3): 651-671 Export BibTexEndNote
Metals like iron, copper, zinc, and manganese are trace elements essential for the survival and growth of diverse organisms. They influence the protease activity, immune response, physiological processes, and anti-infection mechanism in organisms. During bacterial infection, the host can limit or increase the availability of metal ions in the internal environment to inhibit bacterial proliferation. Meanwhile, bacteria have evolved various transport systems to adapt to the changes in metal ion levels in the host. The metal ion efflux systems exhibit distinctive efflux patterns due to variations in the structural and biochemical properties. We reviewed the available articles and our own research findings about the bacterial efflux systems of iron, copper, zinc, and manganese ions, aiming to provide an overview of the progress in the research on the regulatory mechanisms governing bacterial metal homeostasis. This review of metal ion efflux systems across different bacteria highlights the adaptation that enables bacterial survival in diverse host environments.
Citation
DONG Xinnan, DENG Simin, SONG Houhui, XU Jiali, CHENG Changyong. Bacterial metal ion efflux systems and metal homeostasis. [J]. Acta Microbiologica Sinica, 2024, 64(3): 672-686 Export BibTexEndNote
Antibiotics are secondary metabolites produced by microorganisms during the stationary phase. They are widely used in the clinical treatment of bacterial infections because of their ability to kill bacteria or inhibit bacterial growth. In the long-term evolutionary process, bacteria have adopted several strategies to cope with the threats of antibiotics in the environment. In addition to the well-known antibiotic resistance, bacteria can develop tolerance and persistence to antibiotics, which seriously affects the clinical efficacy of antibiotics. Guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp) (herein collectively referred to as ppGpp) are the alarmone signal molecules produced by bacteria in response to unfavorable environmental conditions such as nutritional starvation. ppGpp can regulate transcription globally and enable bacteria to survive in unfavorable conditions. An increasing number of studies have shown that ppGpp is closely related to antibiotic stress response. On this basis, this review summarizes the synthesis, hydrolysis, and mechanism of action of ppGpp in bacteria, with emphasis on the role of ppGpp in antibiotic stress response. This review aims to provide new ideas for the development of novel antibiotics.
Citation
HU Xiao, SHEN Penshan, XU Jianping, YU Jiaqi, YIN Jianhua. Research progress in ppGpp-mediated antibiotic stress response. [J]. Acta Microbiologica Sinica, 2024, 64(3): 687-700 Export BibTexEndNote
The non-biodegradable nature of heavy metals (HMs) results in their long-term presence in the environment, leading to severe environmental pollution and posing a threat to human health and ecosystems. Compared with physical and chemical remediation techniques, microbial remediation is praised for the low cost, environmental friendliness, and high efficiency. When facing heavy metal stress or nutrient imbalance, microorganisms are stimulated to produce and secrete extracellular polysaccharides (EPSs). Therefore, the production of EPSs is regarded as one of the important strategies employed by microorganisms to combat HM stress. EPSs not only protect microorganisms in extreme conditions such as low temperature, high temperature, high salinity, or exposure to toxic compounds but also facilitate the communication and transfer of information and substances both inside and outside the cells. EPSs serve as a protective barrier to restrict the entry of HM ions into the cells and as a medium for communication. EPSs contain multiple negatively charged functional groups capable of complexing with HM ions, undergoing ion exchange, and participating in redox reactions, thereby reducing the bioavailability and toxicity of HMs. Microbial EPSs play a significant role in the remediation of HM-contaminated environments. However, there is currently a lack of a systematic review on the synthesis process of microbial EPSs, the mechanisms of the interaction of EPSs with HMs, and the application status of EPSs in the environments with HM stress. This article provides an overview of microbial EPSs and their classification, elaborates on the intracellular and extracellular biosynthesis mechanisms of bacterial EPSs, explores the interactions between microbial EPSs and HMs, and discusses research advances in the use of microbial EPSs for the remediation of HM pollution in water and soil environments. Finally, it looks ahead to the synthesis of EPSs and the role of EPSs in HM remediation, offering support for the further application of microbial EPSs in the remediation of environmental HM pollution.
Citation
MA Ying, JIANG An, SHI Xiaojun, LI Zhenlun, CHEN Xinping. Synthesis of microbial exopolysaccharides and their mechanisms and applications in heavy metal remediation. [J]. Acta Microbiologica Sinica, 2024, 64(3): 701-719 Export BibTexEndNote