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.