Halotolerance mechanisms of the methanotroph Methylomicrobium alcaliphilum

BORDEL SERGIO; SARA CANTERA; RAUL MUÑOZ; PERE REBECA; NURIA FERNANDEZ; ELISA RODRIGUEZ; M. ALEJANDRA MARTINEZ

Biotechnology and Bioengineering

John Wiley and Sons Inc.P.O.Box 18667NewarkNJ 07191-8667

Año: 2020

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. alcali- philum 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 osmopro- tector 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.