Halotolerance mechanisms of the methanotroph Methylomicrobium alcaliphilum

Abstract

Methylomicrobium alcaliphilum is an alkaliphilic and halotolerant methanotroph. The physiological responses of M. alcaliphilum to high NaCl concentrations, were studied using RNA sequencing and metabolic modeling. This study revealed that M. alcaliphilum possesses an unusual respiratory chain, in which complex I is replaced by a Na + extruding NQR complex (highly upregulated under high salinity conditions) and a Na + driven adenosine triphosphate (ATP) synthase coexists with a conventional H + driven ATP synthase. A thermodynamic and metabolic model showing the interplay between these different components is presented. Ectoine is the main osmoprotector used by the cells. Ectoine synthesis is activated by the transcription of an ect operon that contains five genes, including the ectoine hydroxylase coding ectD gene. Enzymatic tests revealed that the product of ectD does not have catalytic activity. A new Genome Scale Metabolic Model for M. alcaliphilum revealed a higher flux in the oxidative branch of the pentose phosphate pathway leading to NADPH production and contributing to resistance to oxidative stress.

Vibrio natriegens genome‐scale modeling reveals insights into halophilic adaptations and resource allocation

“…Cell division protein FtsY was also found to be upregulated. This observation is similar to the increased expression of FtsQ in the halophilic bacterium Methylomicrobium alcaliphilum (Bordel et al , 2020 ).…”

“…A variety of other ABC transporters were found upregulated, including dicarboxylate, amino acid, and ion transporters. This is not unexpected, as some ABC transporters have been found to be osmosensing enzymes and directly related to osmotic adaptations (Wood, 2015;Bordel et al, 2020). Additionally, some of the essential membrane-bound building blocks of V. natriegens' respiratory system were found to be upregulated at 300 mM, such as the Na + -translocating NADH:quinone oxidoreductase, the ATP F0F1 synthase, and cytochrome C. This may indicate that these proteins are better adapted to the transmembrane osmotic forces present at higher salinities, consistent with V. natriegens' general preference for such environments.…”

Transcriptomic and metabolomic responses to carbon and nitrogen sources in Methylomicrobium album BG8

“…Our observation that the NADH oxidoreductases are downregulated in methanol cultures provides further support for this hypothesis; in methanol, MDH-derived electrons can be directly transferred to cytochromes to fuel the electron transport chain (25), reducing the need for the electron-harvesting NADH oxidoreductase complex to power ATP production. There is less evidence for the importance of the PP pathway in methanotrophs, though increased flux through the PP pathway has been shown to satisfy the higher demand for NADPH production in response to oxidative stress in M. alcaliphilum 20Z (26). Other gammaproteobacterial methanotrophs do not show the same preference for the ED or PP pathways when growing on methanol (5, 17), suggesting that some methanol adaptations may be strain-specific, but further investigation of sugar catabolism pathway flux using more targeted analysis will be needed to confirm carbon pathway preferences in M. album BG8.…”

“…The copyright holder for this preprint this version posted February 19, 2021. ; https://doi.org/10.1101/2021.02.18.431927 doi: bioRxiv preprint 13 (26). Other gammaproteobacterial methanotrophs do not show the same preference for the ED or PP pathways when growing on methanol (5,17), suggesting that some methanol adaptations may be strain-specific, but further investigation of sugar catabolism pathway flux using more targeted analysis will be needed to confirm carbon pathway preferences in M. album BG8.…”

Biogeographical distribution and regulation of methanotrophs in Chinese paddy soils

“…Here, salinity was negatively correlated with the number of OTUs, but positively correlated with the relative abundance of Methylocaldum (type I) (p < 0.05) (Figure 6). The Methylomicrobium alcaliphilum (type I) was reported to be halotolerant methanotrophs (Bordel et al, 2020), but the salt tolerance of Methylocaldum needs to be further studied.…”