Carbon dioxide and trace oxygen concentrations impact growth and product formation of the gut bacterium Phocaeicola vulgatus

Abstract

Background: The promising yet barely investigated anaerobic species Phocaeicola vulgatus (formerly Bacteroides vulgatus) plays a vital role for human gut health and effectively produces organic acids. Among them is succinate, a building block for high-value-added chemicals. Cultivating anaerobic bacteria is challenging, and a detailed understanding of P. vulgatus growth and metabolism is required to improve succinate production. One significant aspect is the influence of different gas concentrations. CO₂ is required for the growth of P. vulgatus. However, it is a greenhouse gas that should not be wasted. Another highly interesting aspect is the sensitivity of P. vulgatus towards O₂. In this work, the effects of varying concentrations of both gases were studied in the in-house developed Respiratory Activity MOnitoring System (RAMOS), which provides online monitoring of CO₂, O_2, and pressure under gassed conditions. The RAMOS was combined with a gas mixing system to test CO₂ and O₂ concentrations in a range of 0.25-15.0 vol% and 0.0-2.5 vol%, respectively.

Results: Changing the CO₂ concentration in the gas supply revealed a CO₂ optimum of 3.0 vol% for total organic acid production and 15.0 vol% for succinate production. It was demonstrated that the organic acid composition changed depending on the CO₂ concentration. Furthermore, unrestricted growth of P. vulgatus up to an O₂ concentration of 0.7 vol% in the gas supply was proven. The viability decreased rapidly at concentrations larger than or equal to 1.3 vol% O₂.

Conclusions: The study showed that P. vulgatus requires little CO₂, has a distinct O₂ tolerance and is therefore well suited for industrial applications.

Keywords: Anaerobic fermentation; Carbon dioxide optimum; Gut bacteria; Oxygen tolerance; Phocaeicola (Bacteroides) vulgatus; Short chain fatty acids (SCFA).