Insights into Xylan Degradation and Haloalkaline Adaptation through Whole-Genome Analysis of Alkalitalea saponilacus, an Anaerobic Haloalkaliphilic Bacterium Capable of Secreting Novel Halostable Xylanase

Abstract

The obligately anaerobic haloalkaliphilic bacterium <i>Alkalitalea saponilacus</i> can use xylan as the sole carbon source and produce propionate as the main fermentation product. Using mixed carbon sources of 0.4% (<i>w</i>/<i>v</i>) sucrose and 0.1% (<i>w</i>/<i>v</i>) birch xylan, xylanase production from <i>A. saponilacus</i> was 3.2-fold greater than that of individual carbon sources of 0.5% (<i>w</i>/<i>v</i>) sucrose or 0.5% (<i>w</i>/<i>v</i>) birch xylan. The xylanse is halostable and exhibits optimal activity over a broad salt concentration (2⁻6% NaCl). Its activity increased approximately 1.16-fold by adding 0.2% (<i>v</i>/<i>v</i>) Tween 20. To understand the potential genetic mechanisms of xylan degradation and molecular adaptation to saline-alkali extremes, the complete genome sequence of <i>A. saponilacus</i> was performed with the pacBio single-molecule real-time (SMRT) and Illumina Misseq platforms. The genome contained one chromosome with a total size of 4,775,573 bps, and a G+C genomic content of 39.27%. Ten genes relating to the pathway for complete xylan degradation were systematically identified. Furthermore, various genes were predicted to be involved in isosmotic cytoplasm via the "compatible-solutes strategy" and cytoplasmic pH homeostasis though the "influx of hydrogen ions". The halostable xylanase from <i>A. saponilacus</i> and its genomic sequence information provide some insight for potential applications in industry under double extreme conditions.