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

• Published in: Applied microbiology and biotechnology 2020-12, Vol.104 (24), p.10541-10553
• Main Authors: Xu, Zhen-Xing, Yu, Pei, Liang, Qi-Yun, Mu, Da-Shuai, Du, Zong-Jun
• Format: Article
• Language: English
• Subjects: Agar; Agarase; Algae; Bacteria; Biochemical analysis; Biodegradation; Biomedical and Life Sciences; Biotechnologically Relevant Enzymes and Proteins; Biotechnology; Carbon; Carbon cycle; Carbon sources; Degradation; Enzymatic activity; Gene expression; Genes; Genomes; Glucose; Hydrolase; Industrial applications; Life Sciences; Marine environment; Microbial Genetics and Genomics; Microbiology; Substrates
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-020-10969-2

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 Q1 T , 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 Q1 T , 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 Q1 T was sequenced and annotated with 11 agarases and 2 Nabh genes. • The expression of agar-degrading genes in the strain C. maritimus Q1 T 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.