Sporulation in solventogenic and acetogenic clostridia

Abstract

The Clostridium genus harbors compelling organisms for biotechnological production processes; while acetogenic clostridia can fix C1-compounds to produce acetate and ethanol, solventogenic clostridia can utilize a wide range of carbon sources to produce commercially valuable carboxylic acids, alcohols, and ketones by fermentation. Despite their potential, the conversion by these bacteria of carbohydrates or C1 compounds to alcohols is not cost-effective enough to result in economically viable processes. Engineering solventogenic clostridia by impairing sporulation is one of the investigated approaches to improve solvent productivity. Sporulation is a cell differentiation process triggered in bacteria in response to exposure to environmental stressors. The generated spores are metabolically inactive but resistant to harsh conditions (UV, chemicals, heat, oxygen). In Firmicutes, sporulation has been mainly studied in bacilli and pathogenic clostridia, and our knowledge of sporulation in solvent-producing or acetogenic clostridia is limited. Still, sporulation is an integral part of the cellular physiology of clostridia; thus, understanding the regulation of sporulation and its connection to solvent production may give clues to improve the performance of solventogenic clostridia. This review aims to provide an overview of the triggers, characteristics, and regulatory mechanism of sporulation in solventogenic clostridia. Those are further compared to the current knowledge on sporulation in the industrially relevant acetogenic clostridia. Finally, the potential applications of spores for process improvement are discussed.Key Points• The regulatory network governing sporulation initiation varies in solventogenic clostridia.• Media composition and cell density are the main triggers of sporulation.• Spores can be used to improve the fermentation process.

Clostridium muellerianum sp. nov., a carbon monoxide-oxidizing acetogen isolated from old hay

“… Clostridium acetireducens and Clostridium glycyrrhizinilyticum [28]. The lack of viable spores and presence of sporulation genes is also consistent with the low sporulation rate of acetogenic and solventogenic Clostridium species reported elsewhere [29].…”

Model-driven approach for the production of butyrate from CO2/H2by a novel co-culture ofC. autoethanogenumandC. beijerinckii

“…S1). This pH is close to the optimal pH of C. autoethanogenum (40), and acid re-assimilation and ABE production in C. beijerinckii (41,22). Butyrate was the most abundant product with a stoichiometry of 0.6-0.7 mol of butyrate produced and 0.4-0.5 mol acetate consumed per mol of lactate consumed, similar to the stoichiometry reported for C. saccharobutylicum NCP262 in (37).…”

Heterologous Expression of NoxA Confers Aerotolerance in Clostridium sporogenes

“…However, over time, as oxygen diffused into the medium, the OD of the native strain started to decrease, which we further found to correlate with sporulation. Sporulation in response to oxygen stress has been observed in a range of Clostridium species (Al-Hinai, Jones and Papoutsakis, 2015; Diallo, Kengen and López-Contreras, 2021).…”

“…C. sporogenes fails to completely eradicate tumors because it cannot penetrate the outer edge of tumors where the oxygen level is higher (Mengesha et al, 2007;Mowday et al, 2016).Despite being characterized as obligate anaerobes, sensitivity to oxygen varies widely within the Clostridium genus, with individual species demonstrating an array of different mechanisms for dealing with the presence of oxygen. Some species of Clostridia undergo endosporulation to resist oxygen stress (Diallo, Kengen and López-Contreras, 2021;Morvan et al, 2021). In contrast, C. butyricum expresses NADH and NADPH oxidase in the presence of oxygen (Kawasaki et al, 1998).…”