Abstract
Sphingomonas sp. WG produced WL gum with commercial utility potential in many industries. A hybrid sensor histidine kinase/response regulator WelA was identified to regulate the WL gum biosynthesis, and its function was evaluated by gene deletion strategy. The WL gum production and broth viscosity of mutant ΔwelA was only 44% and 0.6% of wild type strain at 72 h. The transcriptomic analysis of differentially expressed genes showed that WelA was mapped to CckA; ChpT, and CtrA in the CckA-ChpT-CtrA pathway was up-regulated. One phosphodiesterase was up-regulated by CtrA, and the intracellular c-di-GMP was decreased. Most genes involved in WL gum biosynthesis pathway was not significantly changed in ΔwelA except the up-regulated atrB and atrD and the down-regulated pmm. Furthermore, the up-regulated regulators ctrA, flaEY, flbD, and flaF may participate in the regulation of flagellar biogenesis and influenced motility. These results suggested that CckA-ChpT-CtrA pathway and c-di-GMP were involved in WL gum biosynthesis regulation. This work provides useful information on the understanding of molecular mechanisms underlying WL gum biosynthesis regulation.
Highlights
S-88, welan, and diutan are EPSs produced by the genus Sphingomonas sp
One putative hybrid sensor histidine kinase (HK)/response regulator (RR) encoding gene welA was annotated in the genome of Sphingomonas sp
Structural domain analysis by SMART showed that this protein contains two PAS domains, a HisKA domain, a HATPase_c domain, and a receiver domain (REC) domain, suggesting that this protein had both HK and RR domains and might be a hybrid sensor HK/RR
Summary
Exopolysaccharides (EPSs) secreted by many bacterial strains are ubiquitous and have a wide range of industrial applications, including emulsification, thickening, and pharmaceutical applications (Kumar et al, 2007; Freitas et al, 2011; Schmid et al, 2015). Several EPSs such as xanthan, gellan, curdlan, and succinoglucan have been commercially produced and applied in recent years (Lelchat et al, 2015). Sphingans such as gellan, S-88, welan, and diutan are EPSs produced by the genus Sphingomonas sp. S-88, welan, and diutan are EPSs produced by the genus Sphingomonas sp They have a similar repeating tetrasaccharide backbone structure as glucoseglucuronic acid-glucose-rhamnose or mannose (Fialho et al, 2008). It has been proved that the known sphingans with special side chains have unique rheological characteristics and commercial applications in petroleum, food, concrete, and pharmaceutical industries as gelling, emulsifiers, stabilizers, and viscosifiers agents (Fialho et al, 2008).
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