Enrichment of Hydrogen-Oxidizing Bacteria from High-Temperature and High-Salinity Environments

Abstract

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 conditions such as salt and temperature to steer HOB communities to lower diversities, while 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 in serum flasks. Of the six communities, four were enriched under saline (0.0, 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 conditions to evaluate their potential as microbial protein producers. The 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 thermophilic enrichments. Here we show that enriching for HOB while steering the community toward low diversity and maintaining a high quality protein content can be successfully achieved, both in saline and thermophilic conditions. IMPORTANCE Alternative feed and food supply chains are required to decrease water and land use. HOB offer a promising substitute for traditional agricultural practice to produce microbial protein (MP) from residual materials and renewable energy. To safeguard product stability, the composition of the HOB community should be controlled. Defining strategies to maintain the stability of the communities is therefore key for optimization purposes. In this study, we use salt and temperature as independent conditions to stabilize the composition of the HOB communities. Based on the results presented, we conclude that HOB communities can be steered to have low diversity using the presented conditions while producing a desirable protein content with a valuable amino acid profile.

Enrichment of halotolerant hydrogen-oxidizing bacteria and production of high-value-added chemical hydroxyectoine using a hybrid biological–inorganic system

“…Yet, the economic benefits derived from high-value products could potentially compensate for these additional costs. Moreover, other value-added products (such as vitamins, triacylglycerols, and protein) can be harvested as by-products of the extremolytes ( Shteĭnberg and Datsiuk, 1985 ; Zhang et al, 2019 ; Barbosa et al, 2021b ). Additionally, members of halotolerant HOB could serve as a means of removing pollutants, such as phosphate ions, from wastewater ( Barbosa et al, 2021a ).…”

“…Water splitting with Co-P|CoPi catalysts is promoted by increasing the concentration of the phosphate buffer from 36 to 108 mM ( Liu et al, 2016 ); however, previous studies on HBI systems have mainly used media with low-ionic-strength (i.e., phosphate buffer concentration of ≤36 mM) owing to the salt sensitivity of the biocatalysts used (e.g., C. necator and Xanthobacter autotrophicus ) ( Torella et al, 2015 ; Liu et al, 2016 ). Thus, using halotolerant HOB as the biocatalyst could potentially address this limitation ( Barbosa et al, 2021b ).…”

The microbiology of Power-to-X applications

“…was found to dominate saline enrichments, the genus Hydrogenibacillus was found to be predominant in thermophilic enrichments. The thermophilic enrichments had the highest protein content, and increased temperature was assumed to be advantageous against infection of the cultures with pathogens (Barbosa et al 2021).…”

The Species Identification and Genomic Analysis of Haemobacillus shengwangii: A Novel Pathogenic Bacterium Isolated From a Critically Ill Patient With Bloodstream Infection

“…H. schlegelii was originally named Bacillus schlegelii in 1979 ( Schenk and Aragno, 1979 ) and was transferred to be a novel genus due to its massive divergence from other species in the genus Bacillus in 2013 ( Kampfer et al, 2013 ). H. schlegelii was known for its ability of hydrogen-oxidizing ( Barbosa et al, 2020 ) and was classified into order Bacillales and family Bacillaceae with NCBI taxonomy ID of 1484. B. lithotrophica was isolated from a hot spring in Russia and reported as a new taxon in 2013 ( Perevalova et al, 2013 ).…”