Gluconeogenesis plays a critical role in mycobacterial biofilm formation

Abstract

Gluconeogenesis is an important pathway for bacteria and humans as it maintains the glucose levels in the system. These glucose molecules can be utilized as substrates for several cellular functions. Gluconeogenesis genes are important for the intracellular survival and pathogenicity of Mycobacterium tuberculosis (Mtb). A few reports have shown the role of gluconeogenesis in biofilm formation in other bacteria. Similarly, we utilized gluconeogenesis genes and explored their role in biofilm formation in Mtb. For this study, we have taken the pyruvate carboxylase (pca) gene, which catalyzes the conversion of pyruvate into oxaloacetate and diverts the carbon flux into the gluconeogenesis pathway. We observed that the transposon mutant of pca was deficient in pellicle and submerged biofilm formation and was defective in colony morphology. This phenomenon was recovered upon either gene complementation or external addition of glucose into the medium. In addition to glucose, we also observed the regaining of biofilm phenomenon in the case of pyruvate supplementation. These observations led us to hypothesize that the glucose molecules generated from the gluconeogenesis pathway can be utilized to generate carbohydrates or polysaccharides, such as cellulose, which can be integrated into the extracellular polymeric substances of the biofilm matrix. Cellulose, whose primary subunit is glucose, can be synthesized from these generated glucose molecules, thereby integrating into the biofilm matrix of mycobacteria. This study provides a novel mechanism of cellulose production through a non-canonical pathway in Mtb, which is important in the biofilm formation of this pathogenic bacterium.