The extremely thermophilic bacterium Thermus thermophilus HB27 displays lipolytic activity for the hydrolysis of triglycerides. In this study we performed a mutational in vivo analysis of esterases and lipases that confer growth on tributyrin. We interrupted 10 ORFs suspected to encode lipolytic enzymes. Two chromosomal loci were identified that resulted in reduced hydrolysis capabilities against tributyrin and various para-nitrophenyl acyl esters. By implementation of a convenient new one-step method which abstains from the use of selectable markers, a mutant strain with multiple scar-less deletions was constructed by sequentially deleting ORFs TT_C1787, TT_C0340, TT_C0341 and TT_C0904. The quadruple deletion mutant of T. thermophilus exhibited significantly lower lipolytic activity (approximately 25% residual activity compared to wild type strain) over a broad range of fatty acyl esters and had lost the ability to grow on agar plates containing tributyrin as the sole carbon source. Furthermore, we were able to determine the impact of each gene disruption on the lipolytic activity profile in this model organism and show that the esterase activity in T. thermophilus HB27 is due to a concerted action of several hydrolases having different substrate preferences and activities. The esterase-less T. thermophilus multi-deletion mutant from this study can be used as a screening and expression host for esterase genes from thermophiles or metagenomes.
Keywords: Genetic analysis; Lipolytic activity; Novel clean deletion system; T. thermophilus HB27; Thermostable esterase.
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