Genome-Wide Transcriptomic Analysis of N-Caproic Acid Production in Ruminococcaceae Bacterium CPB6 with Lactate Supplementation
Abstract Background: n-Caproic acid (CA) is gaining increased attention due to its high value as a chemical feedstock. Our recent studies have demonstrated that lactate can be an attractive energy substrate for the production of CA. However, little is known about the potential molecular mechanism for CA production triggered by the supplementation of exogenous lactate at the gene transcriptional level. Results: 5% lactate was supplemented into the fermentation with Ruminococcaceae bacterium CPB6 for CA production. Results showed that lactate supplementation led to earlier CA production and higher final CA titer and productivity. Transcriptional analysis was carried out using RNA-Seq for the culture with lactate supplementation compared to the control (without lactate supplementation). It has been indicated that there were only 34 differentially expressed genes (DEGs) between the two groups at the exponential phase, of which 15 were upregulated, and 19 were downregulated by more than two-fold. A total of 245 DEGs were identified between the two groups at the stationary phase, of which 123 were upregulated and 122 were downregulated. These DEGs cover crucial functional categories. Specifically, 5 genes responsible for the reverse β-oxidation pathway, 11 genes encoding ATP-binding cassette (ABC) transporters, 6 genes encoding substrate-binding protein (SBP) and 4 genes encoding phosphotransferase system (PTS) transporters were strikingly upregulated in response to the addition of lactate. These genes would be candidates for future studies aiming at understanding the regulatory mechanism of lactate conversion into CA, as well as for the improvement of CA production in strain CPB6. Conclusion: This study suggested that lactate supplementation can promote CA production by altering the expression patterns of genes involved in the essential metabolic pathways, such as central pyruvate metabolism, the reverse β-oxidation pathway, ABC and PTS transports. The findings presented herein reveal unique insights into the biomolecular effects of lactate on CA production at the gene transcriptional level.