Protein Complex Production in Alternative Prokaryotic Hosts

Mining transcriptome data: Utilization of environmentally regulated promoters for protein expression and purification in Clostridium perfringens

Clostridium perfringens is a Gram-positive pathogen with low GC content. To identify genes that are transcribed at higher levels when the bacteria grow on a surface, we used RNA-seq in a previous study to measure global transcript levels of cells grown in three types of media on both plates and in liquid culture. We found the arcABDC-argR operon is induced >1000-fold when the cells were grown on plates than in liquid brain heart infusion (BHI). In addition, the pyrBICFZDE operon was transcribed >1000-fold higher in liquid BHI than on plates. Biochemical analysis of C. perfringens proteins is usually accomplished by cloning and expressing the relevant genes in Escherichia coli, a Gram-negative bacterium. Here we utilize both the arcA and pyrB promoters to express and purify proteins from C. perfringens plate and liquid-grown cultures, respectively. Three mg of the His-tagged cytoplasmic protein PilM were obtained when the pilM gene was expressed in cells grown on 10 BHI plates using the arcA promoter. Using the pyrB promoter, 0.85 mg of the C. perfringens His-tagged secreted toxin collagenase was purified from the culture supernatant of 500 ml of cells grown in liquid BHI. In the process of constructing clones, we found we can transform C. perfringens strain HN13 directly with DNA from an in vitro ligation mix, bypassing E. coli. These environmentally regulated promoters can be used to express clostridial or other low GC content genes for protein purification without the addition of an inducer molecule.

Heterologous and Homologous Expression of Proteins from Haloarchaea: Denitrification as Case of Study

Haloarchaea (halophilic microbes belonging to the Archaea domain) are microorganisms requiring mid or even high salt concentrations to be alive. The molecular machinery of these organisms is adapted to such conditions, which are stressful for most life forms. Among their molecular adaptations, halophilic proteins are characterized by their high content of acidic amino acids (Aspartate (Asp) and glumate (Glu)), being only stable in solutions containing high salt concentration (between 1 and 4 M total salt concentration). Recent knowledge about haloarchaeal peptides, proteins, and enzymes have revealed that many haloarchaeal species produce proteins of interest due to their potential applications in biotechnology-based industries. Although proteins of interest are usually overproduced in recombinant prokaryotic or eukaryotic expression systems, these procedures do not accurately work for halophilic proteins, mainly if such proteins contain metallocofactors in their structures. This work summarizes the main challenges of heterologous and homologous expression of enzymes from haloarchaea, paying special attention to the metalloenzymes involved in the pathway of denitrification (anaerobic reduction of nitrate to dinitrogen), a pathway with significant implications in wastewater treatment, climate change, and biosensor design.

Pseudomonas putida KT2440 is HV1 certified, not GRAS

Pseudomonas putida is rapidly becoming a workhorse for industrial production due to its metabolic versatility, genetic accessibility and stress-resistance properties. The P. putida strain KT2440 is often described as Generally Regarded as Safe, or GRAS, indicating the strain is safe to use as food additive. This description is incorrect. P. putida KT2440 is classified by the FDA as HV1 certified, indicating it is safe to use in a P1 or ML1 environment.