Age-Dependent Pleomorphism in Mycobacterium monacense Cultures

Area of Science:

• Microbiology
• Cell Biology
• Genetics

Background:

• Cell shape changes are crucial in the mycobacterial life cycle.
• Systematic studies on mycobacterial pleomorphism linked to growth stages are limited.
• Non-tuberculous mycobacteria (NTM) exhibit complex morphological dynamics.

Purpose of the Study:

• To investigate the complete growth cycle of *Mycobacterium monacense* and document cell shape alterations.
• To identify genes involved in mycobacterial cell morphology and their expression patterns.
• To explore the role of the *dnaK* _3 gene in mycobacterial cell shape determination.

Main Methods:

• Culturing *Mycobacterium monacense* in solid and liquid media to observe growth cycles.
• Analyzing genome data to identify genes related to cell morphology.
• Measuring mRNA levels of specific genes at different growth stages.
• Performing gene overexpression and antisense experiments in *Mycobacterium marinum*.
• Utilizing *dnaK* _3-*lacZ* reporter constructs for regulatory analysis.

Main Results:

• Observed cell shape changes from rod to coccoid and the emergence of phase grey to phase bright (PGB) cells during aging.
• Correlated cell shape changes with the bi-phasic growth curves of *M. monacense* in liquid culture.
• Identified *dnaK* _3 as a gene with increased transcript levels in stationary phase cells.
• Exogenous overexpression of *dnaK* _3 in *M. marinum* induced morphological changes and affected PGB cell frequency.
• Demonstrated species-specific differences in *dnaK* _3 regulation using reporter constructs.

Conclusions:

• The *dnaK* _3 gene may play a role in influencing mycobacterial cell shape.
• Regulation of *dnaK* _3 appears to vary between mycobacterial species, impacting its role in morphology.
• Further research is needed to fully elucidate the mechanisms by which *dnaK* _3 affects cell shape.