Connecting Algal Polysaccharide Degradation to Formaldehyde Detoxification

Abstract

Formaldehyde is a toxic metabolite that is formed in large quantities during bacterial utilization of the methoxy sugar 6‐O‐methyl‐d‐galactose, an abundant monosaccharide in the red algal polysaccharide porphyran. Marine bacteria capable of metabolizing porphyran must therefore possess suitable detoxification systems for formaldehyde. We demonstrate here that detoxification of formaldehyde in the marine Flavobacterium Zobellia galactanivorans proceeds via the ribulose monophosphate pathway. Simultaneously, we show that the genes encoding the key enzymes of this pathway are important for maintaining high formaldehyde resistance. Additionally, these genes are upregulated in the presence of porphyran, allowing us to connect porphyran degradation to the detoxification of formed formaldehyde.

Biochemical and structural characterization of a sphingomonad diarylpropane lyase for cofactorless deformylation

“…An alternative paradigm for nonoxidative C–C bond fragmentation producing formaldehyde as a product can be found in aldolases – these enzymes catalyze reversible addition between a carbonyl and an alcohol to produce a β-hydroxy carbonyl. For example, 3-hexulose-6-phosphate synthetase catalyzes the reversible aldol reaction between formaldehyde and D -5-ribulose 5-phosphate, which may work in tandem with 6-phospho-3-hexuloisomerase to shift the reaction equilibrium ( 37 , 38 ). While most bacterial aldolases are divalent metal dependent, eukaryotic aldolases represent a cofactorless system that utilizes a catalytic lysine to form a covalent Schiff-base conjugate ( 39 ).…”

Unique alcohol dehydrogenases involved in algal sugar utilization by marine bacteria

“…It can react with free amino and thiol groups of proteins and nucleic acids, leading to protein and DNA damage as well as cross-link formations (Chen et al 2016 ; Shishodia et al 2018 ; Tayri-Wilk et al 2020 ). It has been shown that higher concentrations of formaldehyde can negatively affect the growth of Z. galactanivorans (Brott et al 2022 ). Thus, reduced growth of the ADH knockout strain could be explained by the potential accumulation of formaldehyde.…”

“…However, this reaction could not be detected. Both organisms harbor other metabolic pathways for the detoxification of formaldehyde (Brott et al 2022 ). For instance, in Z. galactanivorans , the genes encoding the key enzymes of the ribulose monophosphate pathway are upregulated in the presence of porphyran (Brott et al 2022 ), so an accumulation of formaldehyde is unlikely.…”

“…Both organisms harbor other metabolic pathways for the detoxification of formaldehyde (Brott et al 2022 ). For instance, in Z. galactanivorans , the genes encoding the key enzymes of the ribulose monophosphate pathway are upregulated in the presence of porphyran (Brott et al 2022 ), so an accumulation of formaldehyde is unlikely. Eventually, the ADHs might have a completely different biological function, such as the regeneration of NADH (Hilberath et al 2021 ; Kokorin et al 2021 ).…”

“…The deletion mutant of the ADH gene zgal_4674 in Z. galactanivorans Dsij T (collection number DSM-12802) was constructed using a sacB system (Zhu et al 2017 ), as previously described for the deletion variant of the CYP gene (Brott et al 2022 ). Briefly, to delete zgal_4674 , a 2448-bp fragment including the last 43 bp of zgal_4674 and 2405 bp of the downstream sequence was amplified using primers OFT0041 and OFT0043 on genomic DNA from Z. galactanivorans Dsij T .…”