Dynamics and Complexity of Dark Fermentation Microbial Communities Producing Hydrogen From Sugar Beet Molasses in Continuously Operating Packed Bed Reactors

Anna Detman; Daniel Laubitz; Aleksandra Chojnacka; Ewa Wiktorowska-Sowa; Jan Piotrowski; Agnieszka Salamon; Wiktor Kaźmierczak; Mieczysław K Błaszczyk; Albert Barberan; Yongjian Chen; Ewa Łupikasza; Fei Yang; Anna Sikora

doi:10.3389/fmicb.2020.612344

Dynamics and Complexity of Dark Fermentation Microbial Communities Producing Hydrogen From Sugar Beet Molasses in Continuously Operating Packed Bed Reactors

Front Microbiol. 2021 Jan 8:11:612344. doi: 10.3389/fmicb.2020.612344. eCollection 2020.

Authors

Affiliations

¹ Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland.
² Department of Pediatrics, University of Arizona, Tucson, AZ, United States.
³ Department of Biochemistry and Microbiology, Institute of Biology, Warsaw University of Life Sciences, Warsaw, Poland.
⁴ Krajowa Spółka Cukrowa S.A. Production Facility Dobrzelin Sugar Factory, Dobrzelin, Poland.
⁵ Institute of Agricultural and Food Biotechnology, Warsaw, Poland.
⁶ Department of Environmental Science, University of Arizona, Tucson, AZ, United States.
⁷ Faculty of Earth Sciences, University of Silesia in Katowice, Sosnowiec, Poland.

Abstract

This study describes the dynamics and complexity of microbial communities producing hydrogen-rich fermentation gas from sugar-beet molasses in five packed-bed reactors (PBRs). The bioreactors constitute a part of a system producing hydrogen from the by-products of the sugar-beet industry that has been operating continuously in one of the Polish sugar factories. PBRs with different working volumes, packing materials, construction and inocula were tested. This study focused on analysis (based on 16S rRNA profiling and shotgun metagenomics sequencing) of the microbial communities selected in the PBRs under the conditions of high (>100 cm³/g COD of molasses) and low (<50 cm³/g COD of molasses) efficiencies of hydrogen production. The stability and efficiency of the hydrogen production are determined by the composition of dark fermentation microbial communities. The most striking difference between the tested samples is the ratio of hydrogen producers to lactic acid bacteria. The highest efficiency of hydrogen production (130-160 cm³/g COD of molasses) was achieved at the ratios of HPB to LAB ≈ 4:2.5 or 2.5:1 as determined by 16S rRNA sequencing or shotgun metagenomics sequencing, respectively. The most abundant Clostridium species were C. pasteurianum and C. tyrobutyricum. A multiple predominance of LAB over HPB (3:1-4:1) or clostridia over LAB (5:1-60:1) results in decreased hydrogen production. Inhibition of hydrogen production was illustrated by overproduction of short chain fatty acids and ethanol. Furthermore, concentration of ethanol might be a relevant marker or factor promoting a metabolic shift in the DF bioreactors processing carbohydrates from hydrogen-yielding toward lactic acid fermentation or solventogenic pathways. The novelty of this study is identifying a community balance between hydrogen producers and lactic acid bacteria for stable hydrogen producing systems. The balance stems from long-term selection of hydrogen-producing microbial community, operating conditions such as bioreactor construction, packing material, hydraulic retention time and substrate concentration. This finding is confirmed by additional analysis of the proportions between HPB and LAB in dark fermentation bioreactors from other studies. The results contribute to the advance of knowledge in the area of relationships and nutritional interactions especially the cross-feeding of lactate between bacteria in dark fermentation microbial communities.

Keywords: anaerobic digestion; biohydrogen; dark fermentation; hydrogen-producing bacteria; lactic acid bacteria; metagenomic analysis; microbial communities.