Throughout the course of evolution, bacteria have developed signal transduction tools such as two-component systems (TCSs) to meet their demands to thrive even under the most challenging ...environmental conditions. One TCS called MtrAB is commonly found in
and is implicated in cell wall metabolism, osmoprotection, cell proliferation, antigen secretion, and biosynthesis of secondary metabolites. However, precisely how the MtrAB TCS regulates the bacterial responses to external environments remains unclear. Here, we report that the MtrAB TCS regulates the cell envelope response of alkali-tolerant bacterium
sp. strain DQ12-45-1b to extreme alkaline stimuli. We found that under alkaline conditions, an
mutant exhibited both reduced growth and abnormal morphology compared to the wild-type strain. Electrophoretic mobility shift assay analysis showed that MtrA binds the promoter of the
gene critical for cell wall homeostasis, suggesting that MtrA directly controls transcription of this regulator. In conclusion, our findings demonstrate that MtrAB TCS is involved in controlling the bacterial response to alkaline stimuli by regulating the expression of the cell wall homeostasis regulator MraZ in
sp. DQ12-45-1b, providing novel details critical for a mechanistic understanding of how cell wall homeostasis is controlled.
Microorganisms can be found in most extreme environments, and they have to adapt to a wide range of environmental stresses. The two-component systems (TCSs) found in bacteria detect environmental stimuli and regulate physiological pathways for survival. The MtrAB TCS conserved in
is critical for maintaining the metabolism of the cell wall components that protects bacteria from diverse environmental stresses. However, how the MtrAB TCS regulates cell wall homeostasis and adaptation under stress conditions is unclear. Here, we report that the MtrAB TCS in
sp. DQ12-45-1b plays a critical role in alkaline resistance by modulating the cell wall homeostasis through the MtrAB-MraZ pathway. Thus, our work provides a novel regulatory pathway used by bacteria for adaptation and survival under extreme alkaline stresses.
Two-component systems (TCSs) act as common regulatory systems allowing bacteria to detect and respond to multiple environmental stimuli, including cell envelope stress. The MtrAB TCS of ...Actinobacteria is critical for cell wall homeostasis, cell proliferation, osmoprotection, and antibiotic resistance, and thus is found to be highly conserved across this phylum. However, how precisely the MtrAB TCS regulates cellular homeostasis in response to environmental stress remains unclear. Here, we show that the MtrAB TCS plays an important role in the tolerance to different types of cell envelope stresses, including environmental stresses (i.e., oxidative stress, lysozyme, SDS, osmotic pressure, and alkaline pH stresses) and envelope-targeting antibiotics (i.e., isoniazid, ethambutol, glycopeptide, and β-lactam antibiotics) in
sp. DQ12-45-1b. An
mutant strain exhibited slower growth compared to the wild-type strain and was characterized by abnormal cell shapes when exposed to various environmental stresses. Moreover, deletion of
resulted in decreased resistance to isoniazid, ethambutol, and β-lactam antibiotics. Further, Cleavage under targets and tagmentation sequencing (CUT&Tag-seq) and electrophoretic mobility shift assays (EMSAs) revealed that MtrA binds the promoters of genes involved in peptidoglycan biosynthesis (
,
,
), hydrolysis (GJR88_03483, GJR88_4713), and cell division (
). Together, our findings demonstrated that the MtrAB TCS is essential for the survival of
sp. DQ12-45-1b under various cell envelope stresses, primarily by controlling multiple downstream cellular pathways. Our work suggests that TCSs act as global sensors and regulators in maintaining cellular homeostasis, such as during episodes of various environmental stresses. The present study should shed light on the understanding of mechanisms for bacterial adaptivity to extreme environments.
The multilayered cell envelope is the first line of bacterial defense against various extreme environments. Bacteria utilize a large number of sensing and regulatory systems to maintain cell envelope homeostasis under multiple stress conditions. The two-component system (TCS) is the main sensing and responding apparatus for environmental adaptation. The MtrAB TCS highly conserved in Actinobacteria is critical for cell wall homeostasis, cell proliferation, osmoprotection, and antibiotic resistance. However, how MtrAB works with regard to signals impacting changes to the cell envelope is not fully understood. Here, we found that in the Actinobacterium
sp. DQ12-45-1b, a TCS named MtrAB is pivotal for ensuring normal cell growth as well as maintaining proper cell morphology in response to various cell envelope stresses, namely, by regulating the expression of cell envelope-related genes. Our findings should greatly advance our understanding of the adaptive mechanisms responsible for maintaining cell integrity in times of sustained environmental shocks.
Multiple resistance and pH adaptation (Mrp) complexes are sophisticated cation/proton exchangers found in a vast variety of alkaliphilic and/or halophilic microorganisms, and are critical for their ...survival in highly challenging environments. This family of antiporters is likely to represent the ancestor of cation pumps found in many redox-driven transporter complexes, including the complex I of the respiratory chain. Here, we present the three-dimensional structure of the Mrp complex from a Dietzia sp. strain solved at 3.0-Å resolution using the single-particle cryoelectron microscopy method. Our structure-based mutagenesis and functional analyses suggest that the substrate translocation pathways for the driving substance protons and the substrate sodium ions are separated in two modules and that symmetry-restrained conformational change underlies the functional cycle of the transporter. Our findings shed light on mechanisms of redox-driven primary active transporters, and explain how driving substances of different electric charges may drive similar transport processes.
Introduction
Hypoxia is an important characteristic of gastric mucosal diseases, and hypoxia‐inducible factor‐1α (HIF‐1α) contributes to microenvironment disturbance and metabolic spectrum ...abnormalities. However, the underlying mechanism of HIF‐1α and its association with mitochondrial dysfunction in gastric mucosal lesions under hypoxia have not been fully clarified.
Objectives
To evaluate the effects of hypoxia‐induced HIF‐1α on the development of gastric mucosal lesions.
Methods
Portal hypertensive gastropathy (PHG) and gastric cancer (GC) were selected as representative diseases of benign and malignant gastric lesions, respectively. Gastric tissues from patients diagnosed with the above diseases were collected. Portal hypertension (PHT)‐induced mouse models in METTL3 mutant or NLRP3‐deficient littermates were established, and nude mouse gastric graft tumour models with relevant inhibitors were generated. The mechanisms underlying hypoxic condition, mitochondrial dysfunction and metabolic alterations in gastric mucosal lesions were further analysed.
Results
HIF‐1α, which can mediate mitochondrial dysfunction via upregulation of METTL3/IGF2BP3‐dependent dynamin‐related protein 1 (Drp1) N6‐methyladenosine modification to increase mitochondrial reactive oxygen species (mtROS) production, was elevated under hypoxic conditions in human and mouse portal hypertensive gastric mucosa and GC tissues. While blocking HIF‐1α with PX‐478, inhibiting Drp1‐dependent mitochondrial fission via mitochondrial division inhibitor 1 (Mdivi‐1) treatment or METTL3 mutation alleviated this process. Furthermore, HIF‐1α influenced energy metabolism by enhancing glycolysis via lactate dehydrogenase A. In addition, HIF‐1α‐induced Drp1‐dependent mitochondrial fission also enhanced glycolysis. Drp1‐dependent mitochondrial fission and enhanced glycolysis were associated with alterations in antioxidant enzyme activity and dysfunction of the mitochondrial electron transport chain, resulting in massive mtROS production, which was needed for activation of NLRP3 inflammasome to aggravate the development of the PHG and GC.
Conclusions
Under hypoxic conditions, HIF‐1α enhances mitochondrial dysfunction via Drp1‐dependent mitochondrial fission and influences the metabolic profile by altering glycolysis to increase mtROS production, which can trigger NLRP3 inflammasome activation and mucosal microenvironment alterations to contribute to the development of benign and malignant gastric mucosal lesions.
Highlights
Hypoxia‐inducible factor‐1α (HIF‐1α) upregulation under hypoxia promotes mitochondrial fission/dysfunction via METTL3/IGF2BP3‐mediated dynamin‐related protein 1 (Drp1) N6‐methyladenosine methylation and enhances glycolysis via lactate dehydrogenase A in both portal hypertensive gastropathy and gastric cancer.
Drp1‐dependent mitochondrial fission/dysfunction and enhanced glycolysis are associated with alterations in antioxidant enzyme activity and dysfunction of the mitochondrial electron transport chain, resulting in massive mitochondrial reactive oxygen species (mtROS) production.
Massive mtROS production leads to NLRP3 inflammasome activation to promote the development of gastric mucosal lesions.
Hypoxia repair or targeting of the HIF‐1α‐related pathway may be effective treatments for gastric mucosal lesions under hypoxic condition.
Contrasted with other vibration measurement methods, a novel spectroscopical photogrammetric approach is proposed. Two colored light filters and a CCD color camera are used to achieve the function of ...two traditional cameras. Then a new calibration method is presented. It focuses on the vibrating object rather than the camera and has the advantage of more accuracy than traditional camera calibration. The test results have shown an accuracy of 0.02 mm.
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