Enrichment of hydrogen oxidizing bacteria from high temperature and salinity environments

There is an urgent need for sustainable protein supply routes with low environmental footprint. Recently, the use of hydrogen oxidizing bacteria (HOB) as a platform for high quality microbial protein (MP) production has regained interest. This study aims to investigate the added value of using selective forces (salt and temperature) to steer HOB communities to lower diversities, whilst maintaining a high protein content and a high quality amino acid profile. Pressure drop and hydrogen consumption were measured for 56 days to evaluate autotrophy of a total of six communities based on natural selection, in serum flasks. Of the six communities, four were enriched under saline (0.25, 0.5 and 1.0 mol NaCl l-1) and two under thermophilic conditions (65°C). Five communities enriched for HOB were subsequently cultivated in continuously stirred reactors under the same selective pressures to evaluate their potential as microbial protein producers. The crude protein, percentages ranged from 41 to 80 %. The highest protein content was obtained for the thermophilic enrichments. Amino acid profiles were comparable to protein sources commonly used for feed purposes. Members of the genus Achromobacter were found to dominate the saline enrichments while members of the genus Hydrogenibacillus were found to dominate the termophilic enrichments. Here we show that enriching for HOB while steering the community towards low diversity and maintaining a high quality protein content can be successfully achieved; both in saline and thermophilic conditions.