Bacterial chemotaxis towards polysaccharide pectin by pectin-binding protein

Area of Science:

• Microbiology
• Bacterial Chemotaxis
• Molecular Biology

Background:

• Typical bacteria sense low-molecular-weight substances for chemotaxis.
• Gram-negative Sphingomonas sp. strain A1 displays unusual chemotaxis towards polysaccharides like alginate and pectin.

Purpose of the Study:

• To elucidate the mechanism behind macromolecule-induced chemotaxis in Sphingomonas sp. strain A1.
• To identify the specific protein responsible for pectin chemotaxis and assimilation.

Main Methods:

• Complementation of a mutant strain (A1-M5) with a genomic fragment from wild-type strain A1.
• Whole-genome sequencing to identify mutations.
• Gene disruption and complementation experiments.
• Recombinant protein expression, purification, and characterization (differential scanning fluorimetry, UV absorption spectroscopy, binding assays).

Main Results:

• A mutation in the sph1118 gene was identified in the pectin-non-chemotactic mutant A1-M5.
• Disruption of sph1118 abolished pectin chemotaxis and decreased pectin assimilation.
• Complementation with wild-type sph1118 restored chemotaxis and assimilation.
• The SPH1118 protein specifically binds pectin (Kd = 8.5 μM) and is predicted to be a periplasmic pectin-binding protein linked to an ABC transporter.

Conclusions:

• SPH1118 is the first identified protein mediating chemotaxis towards the macromolecule pectin.
• SPH1118 plays a dual role in both sensing pectin for chemotaxis and facilitating its assimilation.
• This discovery offers novel insights into bacterial sensory mechanisms for complex carbohydrates.