GlnR Activated Transcription of Nitrogen Metabolic Pathway Genes Facilitates Biofilm Formation by Mycobacterium abscessus

Objectives: Nitrogen is indispensable for the synthesis of biomacromolecules. The correlation between nitrogen metabolism and Mycobacterium abscessus ( M. abscessus ) biofilm formation is unclear. This study constructed global nitrogen regulator gene GlnR ( Mab_0744 ) knockout ( AglnR ) and complementation ( AglnR :: glnR ) M. abscessus strains.Methods: Global nitrogen regulator gene glnR ( Mab_0744 ) knockout ( AglnR ) and complementation ( AglnR :: glnR ) M. abscessus strains were constructed. Sauton's medium was used to culture M. abscessus pellicle biofilm. To test the antibiotic susceptibility of pellicle biofilm, clarithromycin, amikacin, cefoxitin or imipenem was added to the medium under biofilms after 14 days of incubation. RT-qPCR and ChIPqPCR were performed to analyse the transcriptional regulatory function of GlnR.Results: GlnR knockout decreased the growth rate of planktonic cells, reduced biofilm mass and wrinkle formation, and diminished the resistance of biofilms to antibiotics. However, the susceptibility of planktonic cells to antibiotics was not changed by glnR knockout. The growth rate of planktonic AglnR cells was accelerated by adding nitrogen sources to the medium; the addition of glutamine or sodium glutamate rescued AglnR biofilm morphology and resistance to amikacin, cefoxitin, clarithromycin and imipenem. GlnR bound the promoter region and activated the transcription of eight nitrogen metabolic pathway genes (i.e. glnA, amt, ansP, nirB, nirD, glnD, glnK and narK3 ), which are closely related to glutamine/glutamate biosynthesis and, thus, regulate biofilm formation.Conclusion: This study provides insights into the mechanisms of M. abscessus biofilm formation and its resistance to antibiotics.(c) 2023 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.