Identification and regulation of an alternative PTS for disaccharide utilization in Clostridium acetobutylicum

TL;DR

This study identifies a new transport system in Clostridium acetobutylicum for using disaccharides like cellobiose and explains how it is regulated, which could help improve biofuel production.

Contribution

The paper discovers and characterizes a novel regulatory mechanism involving a ribonucleic antiterminator for disaccharide utilization in C. acetobutylicum.

Findings

The β-glucoside PTS (bglT) is expressed in response to cellobiose and sucrose but is not essential for sugar transport.

The upstream anti-transcriptional termination factor bglG regulates bglT expression through a ribonucleic antiterminator (RAT).

Modifications to the RAT structure affect transcriptional read-through and termination of downstream genes.

Abstract

Clostridium acetobutylicum is an important solventogenic bacterium capable of acetone-butanol-ethanol fermentation by utilizing a variety of carbon sources. It employs the transport systems of the phosphoenolpyruvate:sugar phosphotransferase systems (PTSs) to assimilate various saccharides. Here, we investigated a β-glucoside PTS (bglT) encoded by the bgl operon (bglGTH) in C. acetobutylicum, which showed significant expression in response to cellobiose and sucrose. Interestingly, bglT is not essential for the transport of these sugars, as C. acetobutylicum possesses dedicated PTSs for the uptake of each individual sugar. We further elucidated the regulatory mechanism of bglT, which is governed by an upstream anti-transcriptional termination factor (bglG). A putative ribonucleic antiterminator (RAT) was identified upstream of bglG and bglT. Inactivation of bglG led to consistent read-through frequencies of the genes downstream of the RAT, irrespective of the sugar present. Conversely, complete removal of RAT elevated the transcriptional levels of downstream genes, while partial deletion of RAT, causing a long stem-loop structure (terminator), resulted in transcription termination. These findings provide novel insights into the regulatory mechanisms controlling sugar utilization in C. acetobutylicum.

Cellulose, the most abundant organic compound on Earth, is primarily found in plant cell walls and can be broken down into sugars such as cellobiose. These sugars are crucial for microbial fermentation, especially in biofuel production. Clostridium acetobutylicum, a promising microorganism for producing short-chain alcohol chemicals, can utilize cellulose degradation products as a carbon source for fermentation. This study identifies the transport systems involved in the utilization of cellobiose and other disaccharides in C. acetobutylicum and analyzes their regulatory mechanisms. Understanding these pathways is essential for enhancing biofuel production from plant biomass.

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