Methylaminotrophic Bacteria in Xenic Nanoalgal Cultures: Incidence, Significance, and Role of Methylated Algal Osmoprotectants

Abstract

Bacteria that oxidize methylated amines are ubiquitous in the sea. The likely source of these C₁ substrates is the quaternary ammonium osmoprotectant, glycine betaine, which degrades to release trimethylamine (TMA), dimethylamine (DMA), and monomethylamine (MMA). Each of these compounds are successively oxidized to yield formaldehyde, formate, and CO₂. The release of methylamines from nanoalgae was determined indirectly by the presence of MMA-oxidizing bacteria in cultures of oceanic algae. Of 19 xenic and axenic pairs of unidentified nanoalgal clones, 6 xenic clones (31.6%) as well as one of the “axenic” counterparts contained methylaminotrophs. A larger survey of 70 algal clones from seven algal classes, revealed 43% as positive, while a group of 78 unidentified clones had a similar methylaminotroph incidence of 41%. When 147 of the clones tested were grouped according to their area of isolation, those from presumably less stratified waters had a relatively low incidence of MMA-oxidizing bacteria (mean <42%), while this incidence in algal clones from stratified gyre waters were relatively higher (mean >42%). Algal clones from the pycnocline of the Sargasso Sea had the highest incidence of methylaminotrophs at 83%. These results are discussed in regard to nanoalgai osmotica and an apparent requirement for C₁ bacterial consorts as in situ mineralizers in the stratified upper ocean.

Keywords:

• Monomethylamine
• methylaminotrophs
• nanoalgae
• osmoprotectants
• stratification
• bacterial consorts