Biology subjects

Rissanen, A. J.

Publications and source records attributed to Rissanen, A. J..

3 recordsLinked to original sources

bioRxiv2021

16S rRNA gene sequences of Candidatus Methylumidiphilus (Methylococcales), a putative methanotrophic genus in lakes and ponds

A putative novel methanotrophic genus, Candidatus Methylumidiphilus (Methylococcales), was recently shown to be ubiquitous and one of the most abundant methanotrophic genera in water columns of oxygen-stratified lakes and ponds of boreal and subarctic area. However, it has probably escaped detection in many previous studies using 16S rRNA gene amplicon sequencing due to insufficient database coverage, which is because Ca. Methylumidiphilus lacks cultured representatives and previously analysed metagenome assembled genomes (MAGs) affiliated with it do not contain 16S rRNA genes. Therefore, we screened MAGs affiliated with the genus for their 16S rRNA gene sequences in a recently published lake and pond MAG dataset. Among 66 MAGs classified as Ca. Methylumidiphilus (with completeness over 40% and contamination less than 5%) originating from lakes in Finland, Sweden and Switzerland as well as from ponds in Canada, we could find 5 MAGs each containing one 1532 bp long sequence spanning the V1-V9 regions of the 16S rRNA gene. After removal of sequence redundancy, this resulted in two unique 16S rRNA gene sequences. These sequences represented two different putative species, i.e. Ca. Methylumidiphilus alinenensis (Genbank accession: OK236221) as well as another so far unnamed species of Ca. Methylumidiphilus (Genbank accession: OK236220). We suggest that including these two sequences in reference databases will enhance 16S rRNA gene - based detection of members of this genus from environmental samples.

ecology↗

bioRxiv2021

A two-staged bacterial process coupling methanotrophic and heterotrophic bacteria for 1-alkene production from methane

Methane (CH4) is a sustainable carbon feedstock source for aerobic CH4-oxidizing bacteria (methanotrophs) to produce value-added chemicals. Under substrate-limited (e.g., CH4, oxygen and nitrogen) conditions, CH4 oxidation results in the production of various short-chain organic acids and platform chemicals. These CH4-derived products could be broadened by utilizing them as a feedstock for heterotrophic bacteria. As a proof of concept, a two-stage system for CH4 abatement and 1-alkene production was developed in this study. Types I and II methanotrophs, i.e., Methylobacter tundripaludum SV96 and Methylocystis rosea SV97, respectively, were investigated in batch tests under different CH4 and air supplementation schemes. CH4 oxidation under either microaerobic or aerobic conditions induced the production of formate, acetate, succinate, and malate in M. tundripaludum SV96, accounting for 4.8-7.0% of consumed CH4-carbon while M. rosea SV97 produced the same compounds except for malate, and with lower efficiency than M. tundripaludum SV96, accounting for 0.7-1.8% of consumed CH4-carbon For the first time, the organic acids-rich spent media of methanotrophs were successfully used for 1-alkene production using engineered Acinetobacter baylyi ADP1 tesA-undA cells. The highest yield of 1-undecene was obtained from spent medium of M. tundripaludum SV96 at 68.9 {+/-} 11.6 mol mol Csubstrate-1.

microbiology↗

bioRxiv2021

Nitrate enhances anaerobic oxidation of methane in boreal lake sediments

The identity of electron acceptors in promoting anaerobic oxidation of methane (AOM) in the sediments of boreal lakes is currently unknown. Here, we studied the AOM rate of sediment slurries collected from three profundal stations of a nitrate-rich, oligo-mesotrophic, boreal lake (Lake Paajarvi, Finland), under varying nitrate concentrations using 13C-labelling. Furthermore, vertical profiles of the sediment and porewater geochemistry, and the microbial communities (16S rRNA gene and shotgun metagenomic sequencing) were analyzed. Despite geochemical data indicating that simultaneous consumption of nitrate and methane took place at the sediment layers chosen for incubations, AOM rate was not enhanced by nitrate amendments at either of the stations. AOM rate was much higher at the shallow Station 1 (0.9-6.8 nmol C cm-3 d-1) with high contents of labile phytoplankton-derived organic matter, than at the deeper stations, Station 2 (0-0.3 nmol C cm-3 d-1) and 3 (0-0.2 nmol C cm-3 d-1). Accordingly, a higher relative abundance of methanotrophic archaea (Candidatus Methanoperedens) and bacteria (Methylococcales) were observed in the layers chosen for incubations at Station 1 than at the other stations. Besides nitrate, the geochemical profiles indicated that AOM was potentially coupled with iron or sulfate reduction at all stations. Furthermore, putative nitrite-reducing methanotrophs (Ca. Methylomirabilis) were the most abundant methanotrophs above the incubation layer at Station 2 and 3, which suggests that nitrite reduction also plays a role in driving AOM in the study lake. We conclude that AOM is not uniquely coupled to nitrate reduction in sediments of nitrate-rich, oligo-mesotrophic, boreal lakes.

ecology↗