Bacterial chemotaxis towards polysaccharide pectin by pectin-binding protein

Hidenori Konishi,Wataru Hashimoto,Masahiro Kobayashi,Mamoru Hio,Ryuichi Takase

doi:10.1038/s41598-020-60274-1

Hidenori Konishi, Wataru Hashimoto + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-60274-1

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Journal: Scientific Reports	Publication Date: Mar 4, 2020
Citations: 15	License type: open-access

Affiliation: Kyoto University

Abstract

As opposed to typical bacteria exhibiting chemotaxis towards low-molecular-weight substances, such as amino acids and mono/oligosaccharides, gram-negative Sphingomonas sp. strain A1 shows chemotaxis towards alginate and pectin polysaccharides. To identify the mechanism of chemotaxis towards macromolecules, a genomic fragment was isolated from the wild-type strain A1 through complementation with the mutant strain A1-M5 lacking chemotaxis towards pectin. This fragment contained several genes including sph1118. Through whole-genome sequencing of strain A1-M5, sph1118 was found to harbour a mutation. In fact, sph1118 disruptant lost chemotaxis towards pectin, and this deficiency was recovered by complementation with wild-type sph1118. Interestingly, the gene disruptant also exhibited decreased pectin assimilation. Furthermore, the gene product SPH1118 was expressed in recombinant E. coli cells, purified and characterised. Differential scanning fluorimetry and UV absorption spectroscopy revealed that SPH1118 specifically binds to pectin with a dissociation constant of 8.5 μM. Using binding assay and primary structure analysis, SPH1118 was predicted to be a periplasmic pectin-binding protein associated with an ATP-binding cassette transporter. This is the first report on the identification and characterisation of a protein triggering chemotaxis towards the macromolecule pectin as well as its assimilation.

Highlights

As opposed to typical bacteria exhibiting chemotaxis towards low-molecular-weight substances, such as amino acids and mono/oligosaccharides, gram-negative Sphingomonas sp. strain A1 shows chemotaxis towards alginate and pectin polysaccharides
No artificial mutagenesis was performed during isolation[9], these strain A1-M5 cells may spontaneously exhibit deficiency in pectin recognition for exhibiting chemotaxis towards this polysaccharide
Sequence identity of ~50%, some genes in the vicinity of sph1118 are predicted to encode members of the ATP-binding cassette (ABC) transporter system for the import of oligopeptides as follows: SPH1114, ATP-binding protein of the oligopeptide ABC transporter; SPH1115, permease of the oligopeptide ABC transporter; SPH1116, permease of the oligopeptide ABC transporter; SPH1117, solute-binding protein associating with the oligopeptide ABC transporter and SPH1118, a solute-binding protein associating with the oligopeptide ABC transporter

Summary

Introduction

As opposed to typical bacteria exhibiting chemotaxis towards low-molecular-weight substances, such as amino acids and mono/oligosaccharides, gram-negative Sphingomonas sp. strain A1 shows chemotaxis towards alginate and pectin polysaccharides. Tar receptor binds to aspartic acid and maltose ( to maltose-bound proteins, as described later); Tsr receptor to serine and leucine; Trg receptor to ribose and galactose and Tap receptor to dipeptide and pyrimidine[6,7,8] As opposed to these bacteria, the motile strain A1-M5 has been isolated from the non-motile wild-type gram-negative Sphingomonas sp. Alginate is directly incorporated as a polysaccharide into the cytoplasm through the mouth-like pit and ATP-binding cassette (ABC) transporter on the cell surface[13,14]. This mechanism has been focused on as novel macromolecular import machinery that acts independent of extracellular macromolecule-degrading enzymes. To the best of our knowledge, there have been no reports on bacterial chemotaxis towards pectin polysaccharides

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