Lipid News

Bacterial sphingolipids: Perhaps not as rare as we thought?

Eric A. Klein
By Eric A. Klein
Oct. 1, 2019

Among the ways cells adapt to changes in their environment, regulation of the lipidome is critical for maintaining cellular integrity. Species that lack temperature homeostasis adapt by modulating acyl chain saturation to resist changes in membrane fluidity. Bacteria such as Escherichia coli desaturate their fatty acids as temperatures decrease; the double bonds formed by acyl chain desaturation introduce kinks in the fatty acids that inhibit lipid packing and increase membrane fluidity to counteract the effects of lower temperature.

Gram-negative aquatic bacterium Caulobacter crescentusEric Klein’s lab showed that the Gram-negative aquatic bacterium Caulobacter crescentus synthesizes a novel glycosphingolipid when phosphates in its environment are limited.U.S. Department of Energy/Wikimedia Commons

Temperature is not the only environmental variable that necessitates membrane remodeling. In many settings, nutrient availability can vary widely. For example, nutrient levels in fresh-water lakes fluctuate with the seasons, and plant decomposition affects soil. In particular, oscillations in phosphate concentration can limit bacterial growth.

When phosphates are limited, the synthesis of membrane phospholipids becomes an obvious challenge. Studies have shown that alphaproteobacteria, such as Agrobacterium tumefaciens and Mesorhizobium loti, adapt to phosphate starvation by increasing production of diacylglycerol-based glyceroglycolipids and ornithine lipids.

In our lab, we recently showed that the Gram-negative aquatic bacterium Caulobacter crescentus responds to phosphate limitation by synthesizing a novel hexosyl-hexuronosyl-ceramide glycosphingolipid, or GSL. Ceramide-based GSLs are ubiquitous in eukaryotic organisms, but in bacteria they had been observed previously only in the Sphingomonadaceae family, where they function as a substitute for outer-membrane lipopolysaccharides, or LPS. Unlike Sphingomonas species, C. crescentus produces LPS even during phosphate starvation; in this organism, the GSLs appear to play a role in resistance to phage-mediated killing.

Now that we know that bacterial GSLs are not limited to just the Sphingomonadaceae, just how widespread are these lipid species? The honest answer is that we simply don’t know. While the lipidomes of many bacteria have been characterized, our findings in C. crescentus demonstrate that lipid abundance can vary with growth conditions. Indeed, previous characterizations in rich growth media did not identify GSLs in C. crescentus.

Another major challenge is that, unlike for eukaryotes, we do not know which enzymes are responsible for ceramide synthesis in prokaryotes. Only the enzyme that catalyzes the first step of ceramide synthesis, serine palmitoyltransferase, has clear homologues in bacteria as described in a recent review by Dominic Campopiano and colleagues. This implies that either (1) bacteria carry out the same synthetic chemistry as eukaryotes, but these enzymes diverged so long ago that the functionally equivalent proteins cannot be identified by sequence homology or (2) bacterial ceramide synthesis evolved independently using novel enzymes and/or synthetic pathways. If the genes required for ceramide synthesis are identified, researchers will be able to take a bioinformatic approach to finding additional species that might produce these lipids.

A growing body of work demonstrates that bacterially produced sphingolipids may play an important role in aspects of human health such as gut homeostasis and oral pathology. Uncovering the mechanism of prokaryotic ceramide synthesis will help determine how widespread these lipids are in bacteria and also may provide a novel route for pharmacological intervention.

Enjoy reading ASBMB Today?

Become a member to receive the print edition monthly and the digital edition weekly.

Learn more
Eric A. Klein
Eric A. Klein

Eric A. Klein is an assistant professor in the biology department and the Center for Computational and Integrative Biology at Rutgers University–Camden.

Related articles

‘Fatty retina’: A root cause of vision loss in diabetes?
Clay Semenkovich & Rithwick Rajagopal
Targeting cardiolipin modification in a genetic disorder
Arianna F. Anzmann, Olivia Sniezek & Hilary Vernon
A surprising modification lowers the lipid binding affinity of a membrane trafficking protein
Jefferson Knight, Colin T. Shearn & Cisloynny Beauchamp–Pérez
Tour de flippase
Todd R. Graham

Get the latest from ASBMB Today

Enter your email address, and we’ll send you a weekly email with recent articles, interviews and more.

Latest in Science

Science highlights or most popular articles

Antidepressant fluvoxamine can keep COVID-19 patients out of the hospital
News

Antidepressant fluvoxamine can keep COVID-19 patients out of the hospital

Dec. 4, 2021

A 10-day course may work as an easy at-home treatment for early COVID-19, a clinical trial finds.

Michel strives to be a better mentor
Award

Michel strives to be a better mentor

Dec. 1, 2021

Lea Michel has won the ASBMB Early-Career Leadership Award for her commitment to advancing the careers of women in biochemistry and molecular biology.

A new way of looking at HDL in pregnancy
Journal News

A new way of looking at HDL in pregnancy

Nov. 30, 2021

Researchers at the University of Cincinnati College of Medicine explore the compositional complexity of high-density lipoprotein in expectant mothers.

How a tiny pet store fish became the center of neuroscience research
News

How a tiny pet store fish became the center of neuroscience research

Nov. 27, 2021

The tropical zebrafish is used extensively in genetics, neuroscience and development labs worldwide.

Science is a human endeavor
Essay

Science is a human endeavor

Nov. 26, 2021

The author learned some difficult and important lessons when he decided to pursue errors in a Nobel laureate’s work.

‘Fatty retina’: A root cause of vision loss in diabetes?
Lipid News

‘Fatty retina’: A root cause of vision loss in diabetes?

Nov. 25, 2021

Abnormalities of lipid metabolism are common in diabetes, so the authors reasoned that the retina might switch its programming in response to an abundance of fuel.