Notice: eScholarship will undergo scheduled maintenance from Tuesday, January 21 to Wednesday, January 22. Some functionality may not be available during this time. Learn more at eScholarship Support.
Pseudomonas putida have emerged as promising biocatalysts for the conversion of sugars and aromatics obtained from lignocellulosic biomass. Understanding the role of carbon catabolite repression (CCR) in these strains is critical to optimize biomass conversion to fuels and chemicals. The CCR functioning in P. putida M2, a strain capable of consuming both hexose and pentose sugars as well as aromatics, was investigated by cultivation experiments, proteomics, and CRISPRi-based gene repression. Strain M2 co-utilized sugars and aromatics simultaneously; however, during co-cultivation with glucose and phenylpropanoid aromatics ( p- coumarate and ferulate), intermediates (4-hydroxybenzoate and vanillate) accumulated, and substrate consumption was incomplete. In contrast, xylose-aromatic consumption resulted in transient intermediate accumulation and complete aromatic consumption, while xylose was incompletely consumed. Proteomics analysis revealed that glucose exerted stronger repression than xylose on the aromatic catabolic proteins. Key glucose (Eda) and xylose (XylX) catabolic proteins were also identified at lower abundance during co-cultivation with aromatics implying simultaneous catabolite repression by sugars and aromatics. Downregulation of crc via CRISPRi led to faster growth and uptake of glucose and p -coumarate in the CRISPRi strains compared to the control while no difference was observed on xylose + p -coumarate. The increased abundance of the Eda and amino acids biosynthesis proteins in the CRISPRi strain further supported these observations. Lastly, small RNAs (sRNAs) sequencing results showed that CrcY and CrcZ homologues levels in M2, previously identified in P. putida strains, were lower under strong CCR (glucose + p -coumarate) condition compared to when repression was absent ( p -coumarate or glucose only).
IMPORTANCE
A newly isolated Pseudomonas putida strain, P. putida M2, can utilize both hexose and pentose sugars as well as aromatics making it a promising host for the valorization of lignocellulosic biomass. Pseudomonads have developed a regulatory strategy, carbon catabolite repression, to control the assimilation of carbon sources in the environment. Carbon catabolite repression may impede the simultaneous and complete metabolism of sugars and aromatics present in lignocellulosic biomass and hinder the development of an efficient industrial biocatalyst. This study provides insight into the cellular physiology and proteome during mixed-substrate utilization in P. putida M2. The phenotypic and proteomics results demonstrated simultaneous catabolite repression in the sugar-aromatic mixtures while the CRISPRi and sRNA sequencing demonstrated the potential role of the crc gene and small RNAs in carbon catabolite repression.
