Abstract
In particular niches of the marine environment, such as abyssal trenches, icy waters and hot vents, the base of the food web is composed of bacteria and archaea that have developed strategies to survive and thrive under the most extreme conditions. Some of these organisms are considered “extremophiles” and modulate the fatty acid composition of their phospholipids to maintain the adequate fluidity of the cellular membrane under cold/hot temperatures, elevated pressure, high/low salinity and pH. Bacterial cells are even able to produce polyunsaturated fatty acids, contrarily to what was considered until the 1990s, helping the regulation of the membrane fluidity triggered by temperature and pressure and providing protection from oxidative stress. In marine ecosystems, bacteria may either act as a sink of carbon, contribute to nutrient recycling to photo-autotrophs or bacterial organic matter may be transferred to other trophic links in aquatic food webs. The present work aims to provide a comprehensive review on lipid production in bacteria and archaea and to discuss how their lipids, of both heterotrophic and chemoautotrophic origin, contribute to marine food webs.
Highlights
The conditions of the marine environment led to the development of specialized lipid molecules responsible for the formation of membranes and storage of energy, and in higher organisms, for tissue formation, reproduction and growth
Lipids play an important role in the maintenance of cell viability under stressful conditions, as membrane fluidity is maintained by alterations in the fatty acid composition of the membrane phospholipids through a mechanism called ―homeoviscous adaptation‖ [22]
Extremophiles present alterations in fatty acid composition of the cellular membranes and produce specialized lipids, allowing them to survive under conditions that kill most of the other micro-organisms
Summary
The conditions of the marine environment led to the development of specialized lipid molecules responsible for the formation of membranes and storage of energy, and in higher organisms, for tissue formation, reproduction and growth. Archaeal membranes have bipolar lipids containing two polar heads linked by isoprenoid chains and ether linkages to glycerol This allows for the formation of a monolayer membrane, which is likely to be responsible for the ability of these cells to thrive in extreme environments. In the field of marine lipidology, these different approaches can be used to search for new fatty acid structures and new sources of polyunsaturated fatty acids (PUFAs), in studying the role of the several fatty acids in cell membranes and their biosynthetic pathways and in finding the best fatty acid biomarkers or fatty acid ratios to assess trophic transfer in ecosystems [6]. As pointed out in a review by Valentine and Valentine, PUFAs have significant structural roles in bacterial membranes, including: regulatory function triggered by temperature and pressure; EPA-enriched membranes support a respiratory lifestyle dependent on proton bioenergetics; and contribution to increased fluidity of the cellular membrane under marine conditions [16]. The use of bacterial fatty acids or bacterial fatty acid ratios may be used to disclose bacterial connections to the marine food web and its importance to supply materials and energy to the higher trophic levels
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