Inducible expression of agar-degrading genes in a marine bacterium Catenovulum maritimus Q1T and characterization of a β-agarase.

Abstract

Agar-degrading bacteria are crucial drivers for the carbon cycle in the marine environments due to their ability that use algae as a carbon source. Although numerous agar-degrading bacteria and agarases have been reported, little is known about expression levels of agar-degrading genes in wild strains. Here, the genome of an agar-hydrolyzing marine bacterium, Catenovulum maritimus Q1T, was sequenced and annotated with 11 agarase and 2 neoagarooligosaccharide hydrolase genes. Quantitative PCR revealed that all the annotated agar-degrading genes were expressed consistently that initially upregulated and then gradually downregulated under agarose induction. Moreover, the presence of glucose inhibited the agar-degrading ability, in terms of both gene expression and enzymatic activity. These facts indicated the agar-degrading ability of wild bacteria was mainly induced by agarose and repressed by the available carbon source. Additionally, a β-agarase, AgaQ1, belonging to the GH16 family, with high expression in strain Q1T, was cloned and characterized. Biochemical analysis showed that the recombinant AgaQ1 was substrate-specific, yielding neoagarotetraose and neoagarohexaose as the main products. It exhibited optimal activity at 40 °C, pH 8.0, and an agarose concentration of 1.6% (w/v). Besides, AgaQ1 showed a high-specific activity (757.7 U/mg) and stable enzymatic activity under different ion or agent treatments; thus, AgaQ1 has great potential in industrial applications. KEY POINTS: • The genome of C. maritimus Q1T was sequenced and annotated with 11 agarases and 2 Nabh genes. • The expression of agar-degrading genes in the strain C. maritimus Q1T was induced by agarose. • Glucose was the carbon source utilized prior to agarose for bacterial growth. • A β-agarase, AgaQ1, with high expression and activity was identified.