Abstract
The Solfatara volcano near Naples (Italy), the origin of the recently discovered verrucomicrobial methanotroph Methylacidiphilum fumariolicum SolV was shown to contain ammonium () at concentrations ranging from 1 to 28 mM. Ammonia (NH3) can be converted to toxic hydroxylamine (NH2OH) by the particulate methane monooxygenase (pMMO), the first enzyme of the methane (CH4) oxidation pathway. Methanotrophs rapidly detoxify the intermediate NH2OH. Here, we show that strain SolV performs ammonium oxidation to nitrite at a rate of 48.2 nmol .h−1.mg DW−1 under O2 limitation in a continuous culture grown on hydrogen (H2) as an electron donor. In addition, strain SolV carries out nitrite reduction at a rate of 74.4 nmol .h−1.mg DW−1 under anoxic condition at pH 5–6. This range of pH was selected to minimize the chemical conversion of nitrite () potentially occurring at more acidic pH values. Furthermore, at pH 6, we showed that the affinity constants (Ks) of the cells for NH3 vary from 5 to 270 μM in the batch incubations with 0.5–8% (v/v) CH4, respectively. Detailed kinetic analysis showed competitive substrate inhibition between CH4 and NH3. Using transcriptome analysis, we showed up-regulation of the gene encoding hydroxylamine dehydrogenase (haoA) cells grown on H2/ compared to the cells grown on CH4/ which do not have to cope with reactive N-compounds. The denitrifying genes nirk and norC showed high expression in H2/ and CH4/ grown cells compared to cells growing at μmax (with no limitation) while the norB gene showed downregulation in CH4/ grown cells. These cells showed a strong upregulation of the genes in nitrate/nitrite assimilation. Our results demonstrate that strain SolV can perform ammonium oxidation producing nitrite. At high concentrations of ammonium this may results in toxic effects. However, at low oxygen concentrations strain SolV is able to reduce nitrite to N2O to cope with this toxicity.
Highlights
Methane (CH4) is a powerful greenhouse gas, which is released in to the atmosphere both from natural and anthropogenic sources (Conrad, 2009)
It has been shown that growth of the new acidophilic methanotrophic bacterium Methylacidiphilum fumariolicum SolV is strictly dependent on the presence of lanthanides acting as a cofactor of the methanol dehydrogenase (Keltjens et al, 2014; Pol et al, 2014)
We showed that the nitric oxide (NO)−2, NO and N2O concentrations were elevated by increasing the pH from 3 to 5.5 in the presence of
Summary
Methane (CH4) is a powerful greenhouse gas, which is released in to the atmosphere both from natural and anthropogenic sources (Conrad, 2009). New species of mesophilic acidophilic verrucomicrobial methanotrophs were isolated and characterized from a volcanic region in Italy and the new genus Methylacidimicrobium was proposed (Sharp et al, 2014; van Teeseling et al, 2014). This finding expands the diversity of verrucomicrobial methanotrophs and demonstrates that they could be present in more ecosystems than formerly supposed (Chistoserdova et al, 2009). The new verrucomicrobial strains from both genera were shown to be autotrophs that use CH4 as the sole energy source and fix CO2 using the CalvinBenson-Bassham Cycle (Khadem et al, 2011; Sharp et al, 2012, 2013, 2014; van Teeseling et al, 2014), and strain SolV was shown to be able to fix N2 (Khadem et al, 2010)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
