Brachybacterium muris Detected in a Hepatocellular Carcinoma Patient with Pleural Effusion: A Case Report.

Background: Brachybacterium muris is a species of Gram positive and strictly aerobic bacterium. It was first reported in 2003 after being isolated from the liver of a laboratory mouse strain. It was also found on human skin and nasal cavity. Herein, we present the first case pleural effusion infection in humans caused by Brachybacterium muris. Case Presentation: A 65-year-old man was admitted to our hospital for a 4-week history of fever, accompanied by chills, occasional abdominal pain, occasional chest tightness and shortness of breath. On the day of hospitalization, thoracentesis was performed and 1000mL of yellow cloudy fluid was released. Result of pleural fluid culture was positive and B. muris was identified using 16S rDNA amplification and sequence comparisons. Conclusion: To our knowledge, this is the first report of pleural effusion infection caused by B. muris. B. muris can be pathogenic in humans.

The adaptive mechanism of halophilic Brachybacterium muris in response to salt stress and its mitigation of copper toxicity in hydroponic plants.

Serious environmental pollution of heavy metals has attracted people's attention in recent years and halophiles seem to be potential bioremediation in the controlling of heavy metals contamination. In this study, the adaptive mechanism of halophilic Brachybacterium muris (B. muris) in response to salt stress and its mitigation of copper (Cu) toxicity in hydroponic plants were investigated. The cell morphology was observed using transmission electron microscopy. The cell membrane composition and fluidity were examined by the combination of gas chromatography, gas chromatography-mass spectrometry, ultra-high performance liquid chromatography-mass spectrometry, and fluorescence spectrophotometry. Moreover, the metabolic pathways of B. muris in response to salt stress were analyzed using the prokaryotic transcriptomics approach. A hydroponic co-culture model was further conducted to explore the effects of B. muris on wheat seedlings subjected to Cu toxicity. It was found that B. muris can respond to high osmotic pressure by improving the cell membrane fluidity, altering the cell morphology and cell membrane compositions. The proportion of unsaturated fatty acids, phosphatidylethanolamine, and phosphatidylinositol in B. muris cell membranes increased significantly, while zymosterol, fecosterol, and ergosterol contents decreased under a high salinity situation. Further transcriptomic analysis showed that genes encoding L-glutamate synthase, glutamate ABC transporter ATP-binding protein, and sodium cotransporter were up-regulated, indicating that both the synthesis and transport of glutamate were significantly enhanced under high osmotic pressure. Additionally, B. muris alleviated the inhibitory effect of Cu2+ on wheat seedlings' growth, causing a 30.14% decrease in H2O2 content and a significant increase of 83.86% and 45.96% in POD activity and GSH content in wheat roots, respectively. The findings of this study suggested that the salt-tolerant B. muris may serve as a promising strategy for improving the bioremediation of metal-contaminated saline water and soils.