Abstract
The highly conserved ATP-dependent Lon protease plays important roles in diverse biological processes. The lon gene is usually nonessential for viability; however, lon mutants of several bacterial species, although viable, exhibit cellular defects. Here, we show that a lack of Lon protease causes pleiotropic effects in the rice pathogen Burkholderia glumae. The null mutation of lon produced three colony types, big (BLONB), normal (BLONN), and small (BLONS), in Luria-Bertani (LB) medium. Colonies of the BLONB and BLONN types were re-segregated upon subculture, while those of the BLONS type were too small to manipulate. The BLONN type was chosen for further studies, as only this type was fully genetically complemented. BLONN-type cells did not reach the maximum growth capacity, and their population decreased drastically after the stationary phase in LB medium. BLONN-type cells were defective in the biosynthesis of quorum sensing (QS) signals and exhibited reduced oxalate biosynthetic activity, causing environmental alkaline toxicity and population collapse. Addition of excessive N-octanoyl-homoserine lactone (C8-HSL) to BLONN-type cell cultures did not fully restore oxalate biosynthesis, suggesting that the decrease in oxalate biosynthesis in BLONN-type cells was not due to insufficient C8-HSL. Co-expression of lon and tofR in Escherichia coli suggested that Lon negatively affects the TofR level in a C8-HSL-dependent manner. Lon protease interacted with the oxalate biosynthetic enzymes, ObcA and ObcB, indicating potential roles for the oxalate biosynthetic activity. These results suggest that Lon protease influences colony morphology, growth, QS system, and oxalate biosynthesis in B. glumae.
Highlights
The ATP-dependent protease Lon is highly conserved in prokaryotes and eukaryotes and is involved in diverse biological processes [1]
When a colony of the BLONN type was subcultured in LB medium, cells were segregated into the BLONB, BLONN, Fig 1
Such segregation of the BLONB and BLONN types did not change in M9 minimal medium supplemented with 0.2% glucose (Fig 1E), nutrient broth medium (Fig 1F), King’s B medium (Fig 1G), and LB supplemented with 100 mM HEPES (Fig 1H)
Summary
The ATP-dependent protease Lon is highly conserved in prokaryotes and eukaryotes and is involved in diverse biological processes [1]. Lon was first identified in Escherichia coli and derived its name from the long, non-septate filamentation phenotype of the lon mutant [2]. Studies have shown that Lon plays an important role in the degradation of abnormal or unstable regulatory proteins as a quality control protease [1]. Roles of Lon protease for morpho-physiological traits in the rice pathogen Burkholderia glumae. Research Foundation of Korea (NRF) funded by the Ministry of the Education (2021R1I1A1A01040314) (E.G.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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