Insights into Clostridium tetani: From genome to bioreactors.

Tetanus vaccination is of major importance for public health in most countries in the world. The World Health Organization indicated that 15,000 tetanus cases were reported in 2018 (Organization, World Health, 2019). Currently, vaccine manufacturers use tetanus toxin produced by Clostridium tetani fermentation in complex media. The complex components, commonly derived from animal sources, introduce potential variability in cultures. To achieve replicable fermentation and to avoid toxic or allergic reactions from animal-source compounds, several studies have tried to switch from complex to chemically defined media without affecting toxin titers. The present review introduces the current knowledge on i) C. tetani strain diversity, whole-genome sequences and metabolic networks; ii) toxin regulation and synthesis; and iii) culture media, cultivation processes and growth requirements. We critically reviewed the reported data on metabolism in C. tetani and completed comparative genomic and proteomic analyses with other Clostridia species. We integrated genomic data based on whole-genome sequence annotation, supplemented with cofactor specificities determined by protein sequence identity, in a new map of C. tetani central metabolism. This is the first data review that integrates insights from omics experiments on C. tetani. The overview of C. tetani physiology described here could provide support for the design of new chemically defined media devoid of complex sources for toxin production.

Isopropanol production from carbon dioxide in Cupriavidus necator in a pressurized bioreactor.

A bioreactor was designed to provide high gas mass transfer to reach cell and product titres in the g L-1 level from CO2 for realistic, laboratory scale, engineered autotrophic strain evaluation. The design was based on independent CO2, H2 and air inputs and the ability to operate at high pressures. The bioreactor configuration and cultivation strategy enabled growth of Cupriavidus necator strains for long periods, to reach over 3 g L-1 dry cell weight. No negative impact of the high pressure was observed on viability of the strains up to more than 4 bar overpressure. The cultivation was then carried out using an engineered isopropanol producing strain; in this case, 3.5 g L-1 isopropanol was obtained from CO2 as the sole carbon source. This is the first reported demonstration of a successful production from engineered bacteria of product in the g L-1 range on CO2, raising the prospect of future development of CO2-based bioprocesses.