# Exceptionally stable membrane lipid composition of the marine facultative anaerobe and piezotolerant ‘Labilibaculum euxinus’ under variable pressure and nutrients

## TL;DR

This study shows how a deep-sea bacterium maintains stable membrane lipids under high pressure and low nutrients, revealing its resilience in extreme marine conditions.

## Contribution

The study identifies stable lipid composition in a piezotolerant bacterium under variable pressure and phosphate levels, a novel insight into microbial adaptation.

## Key findings

- L. euxinus maintains stable polar headgroup lipid distribution despite high hydrostatic pressure.
- High pressure affects fatty acyl chain unsaturation and cardiolipin abundance.
- Cell elongation under pressure suggests morphological adaptation without lipid composition changes.

## Abstract

The lipid bilayer is a dynamic barrier that plays a critical role as a frontier between cellular elements and the environment. The marine environment presents a unique set of conditions, including variations in nutrient availability, temperature, and high hydrostatic pressure (HHP). To survive these conditions, deep-sea microbes have developed adaptive strategies to preserve the integrity of their lipid membranes, particularly in response to HHP. Here, we assessed these adaptations by determining changes in the membrane lipids of a piezotolerant bacterium, ‘Labilibaculum euxinus’ from the phylum Bacteroidota (family Marinifilaceae) isolated from 2000 meters depth in the Black Sea, under different hydrostatic pressures and phosphate concentrations. Lipid analysis of ‘L. euxinus’ grown in a medium replete in phosphate revealed the presence of lipids with nonphosphate containing amino acid headgroups, such as ornithine lipids, flavolipins, and capnine lipids, typically associated with adaptation to phosphate limitation. Microscopy analysis revealed cell elongation under HHP, suggesting cell adaptation. Despite this morphological change, the distribution of membrane lipids remained stable in terms of polar headgroups. Nevertheless, HHP affected the unsaturation of the fatty acyl chain and the relative abundance of cardiolipins. Our study showcases the adaptability of certain extremophiles, particularly piezotolerant organisms.

This study reveals how deep-sea bacteria adapt their membrane lipids to survive high pressure and nutrient limitations, highlighting the remarkable resilience of microbes in extreme marine environments..