Development of a defined medium for the heterotrophic cultivation of metallosphaera sedula

Abstract

Metallosphaera sedula is an obligate aerobe, thermoacidophilic Crenarchaeon within the order Sulfolobales. As a model organism for CO2 fixation of the genus Metallosphaera it utilizes the 3-Hydroxypropionate/4-Hydroxybutyrate cycle for autotrophic growth.The organism is best known for its lithoautotrophic mode of growth and a process called bioleaching which describes the extraction of heavy metals from ores. The CO2 fixation via the 3-HP/4-HB cycle is the feature of this organism with the most scientific attention in the past because of its incredible potential the pathway itself, but above that the enzymes within have, especially when being heterologously expressed in specific other organisms.In addition to that, M. sedula also has the ability to grow heterotrophically on complex organic molecules, but as a downside is not able to metabolize any kinds of sugar, a metabolic feature that is common within the genus Metallosphaera. Nevertheless, there are some limitations that complex media come with such as contaminations with components of the biological matrix.In this study, the complex media component tryptone could be replaced with a mixture of amino acids. Starting from a complex carbon source, the first defined cultivation medium for the heterotrophic cultivation of M. sedula could be developed. This medium consists of 16 amino acids as carbon and nitrogen sources. After analysis of substrate uptake rates the number of substrates in the medium could be reduced to 5 resulting in the final 5AA medium.Additionally, the lipid pattern of M. sedula grown on complex media was compared to the one of Sulfolobus acidocaldarius.