Abstract
Mycobacterium marinum is a close relative of Mycobacterium tuberculosis that can cause systemic tuberculosis-like infections in ectotherms and skin infections in humans. Sliding motility correlates with biofilm formation and virulence in most bacteria. In this study, we used a sliding motility assay to screen 2,304 transposon mutants of M. marinum NTUH-M6885 and identified five transposon mutants with decreased sliding motility. Transposons that interrupted the type VII secretion system (T7SS) ESX-1-related genes, espE (mmar_5439), espF (mmar_5440), and eccA1 (mmar_5443), were present in 3 mutants. We performed reverse-transcription polymerase chain reaction to verify genes from mmar_5438 to mmar_5450, which were found to belong to a single transcriptional unit. Deletion mutants of espE, espF, espG (mmar_5441), and espH (mmar_5442) displayed significant attenuation regarding sliding motility and biofilm formation. M. marinum NTUH-M6885 possesses a functional ESX-1 secretion system. However, deletion of espG or espH resulted in slightly decreased secretion of EsxB (which is also known as CFP-10). Thus, the M. marinum ESX-1 secretion system mediates sliding motility and is crucial for biofilm formation. These data provide new insight into M. marinum biofilm formation.
Highlights
Mycobacterium marinum is a non-tuberculous photochromogenic mycobacterium
We first constructed a transposon library of M. marinum NTUH-M6885 containing 2,304 mutants to screen for genes associated with sliding motility
We reperformed the same experiment using an equal quantity of bacteria cultured for 7 days (OD600 = 1), and we found that only five mutants had sliding motility defects (Supplementary Figure 2)
Summary
Mycobacterium marinum is a non-tuberculous photochromogenic mycobacterium. It is a close relative of Mycobacterium tuberculosis, and causes systemic tuberculosis-like infections in ectotherms (Solomon et al, 2003; Hagedorn and Soldati, 2007; Alibaud et al, 2011). Researchers first isolated M. marinum from saltwater fish in the 1920s and identified it as a human pathogen in the 1950s (Riera et al, 2015). This species usually occurs in warm saltwater, freshwater, and poikilothermic animals; fish, frogs, and amphibians are its main natural hosts. It grows best at a temperature of 25–35◦C (McArdle et al, 2016). An M. marinum skin infection is referred to as an aquarium granuloma, swimming pool granuloma, or fish tank granuloma (Solomon et al, 2003; Meijer, 2015; Sette et al, 2015)
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