Neutral Lipid Bodies in Prokaryotes: Recent Insights into Structure, Formation, and Relationship to Eukaryotic Lipid Depots

Abstract

Many prokaryotes are able to accumulate large amounts of lipophilic compounds as inclusion bodies in the cytoplasm. Members of most genera synthesize polymeric lipids such as poly(3-hydroxybutyrate) (PHB) or other polyhydroxyalkanoates (PHAs) (125), whereas accumulation of triacylglycerols (TAGs) and wax esters (WEs) in intracellular lipid-bodies is a property of only a few prokaryotes (10). Like the formation of PHAs, TAG and WE biosynthesis is also promoted in response to stress imposed on the cells and during imbalanced growth, for example by nitrogen limitation, if an abundant carbon source is present at the same time. All these lipids act as storage compounds for energy and carbon needed for maintenance of metabolism and synthesis of cellular metabolites during starvation and in particular if growth resumes. Although neutral lipid metabolism in bacteria, especially WE biosynthesis, has attracted increasing biotechnological interest, there has so far been little interest in medical research in the formation of prokaryotic lipid bodies. However, recent findings suggest that lipid body formation and accumulation of TAGs play an important role in the metabolism of the pathogenic bacteria like Mycobacterium tuberculosis (37,52).In contrast to the restricted occurrence of storage TAGs in prokaryotes, intracellular TAGs are widespread in many eukaryotes (34,35,40,53,65,106,112,132,133). In eukaryotes, storage lipids are also deposited as lipid bodies. Their structure and formation have recently been reviewed in detail by several authors, but additional information on prokaryotic lipid-bodies has been only superficial (98,100,151). In contrast, intracellular accumulation of WEs as a storage lipid is a great exception in eukaryotes and occurs only in jojoba (Simmondsia chinensis) (147), and PHAs are not at all synthesized as a storage compound in eukaryotes.The number of studies investigating the enzymatic and structural fundamentals of storage lipid metabolism in bacteria has increased drastically in the last years, providing the knowledge that storage lipids in bacteria have a similar important metabolic function like in eukaryotes. This review will focus on prokaryotic neutral lipid bodies in comparison with the currently discussed models for lipid body structure and their formation in eukaryotes and with PHA inclusions in prokaryotes.

Lipidomics of host–pathogen interactions

“…In fact, they are now considered bonafide organelles with distinct metabolism. Their biogenesis is not fully understood and follows different pathways in bacteria and eukaryotic cells [42]. Triglycerides have been described in Toxoplasma [43] and in mycobacteria from sputum of patients with TB [44].…”

Bioresources for Third-Generation Biofuels

“…The most interesting prokaryote genera in terms of accumulation of TAGs are nocardioforms such as Mycobacterium sp., Nocardia sp., Rhodococcus sp., Micromonospora sp., Dietzia sp., and Gordonia sp, alongside streptomycetes, which accumulate TAGs in the cells and the mycelia. TAGs storage is also frequently shown by members of the gram-negative genus Acinetobacter (although, in this case, WE are the dominant inclusion bodies components) (Waltermann & Steinbüchel, 2010). Within eukaryotes, with the exception of algae, yeasts of the genera Candida (non albicans) (Amaretti et al, 2010), Saccharomyces (Kalscheuer et al, 2004;Waltermann & Steinbüchel, 2010) and Rhodotorula (Cheirsilp et al, 2011) are the most interesting ones to produce biodiesel feedstocks.…”

“…TAGs storage is also frequently shown by members of the gram-negative genus Acinetobacter (although, in this case, WE are the dominant inclusion bodies components) (Waltermann & Steinbüchel, 2010). Within eukaryotes, with the exception of algae, yeasts of the genera Candida (non albicans) (Amaretti et al, 2010), Saccharomyces (Kalscheuer et al, 2004;Waltermann & Steinbüchel, 2010) and Rhodotorula (Cheirsilp et al, 2011) are the most interesting ones to produce biodiesel feedstocks. Steinbüchel and collaborators have worked on the heterologous expression of the non specific acyl transferase WS/DGAT from Acinetobacter calcoaceticus ADP1 in Saccharomyces cerevisiae H1246 (a mutant strain unable of accumulating TAGs) (Kalscheuer et al, 2004).…”

“…But, as occurred with microalgae, not all species are suitable for biodiesel production owing to differences in the kind of storage lipids. Thus, as stated by Waltermann & Steinbüchel (2010), many prokaryotes synthesize polymeric compounds such as poly(3-hydroxybutyrate) (PHB) or other polyhydroxyalkanoates (PHAs), whereas only a few genera show accumulation of triacylglycerols (TAGs) and wax esters (WEs) in the form of intracellular lipid bodies. On the other hand, storage TAGs are often found in eukaryotes, while PHAs are absent, and WE accumulation has only been reported in jojoba (Simmondsia chinensis).…”

Role of bioactive lipid mediators in obese adipose tissue inflammation and endocrine dysfunction

“…Lipid droplets (LD) (also called lipid bodies, oil bodies or adiposomes) are considered a bona fide organelle present in almost all vertebrate cells, some plant cells and several yeasts and prokaryotes (Waltermann and Steinbuchel, 2005;Murphy, 2001). LD are composed of a hydrophobic core, mainly consisting of neutral lipids such as TAG and cholesterol esters surrounded by a phospholipid monolayer (as opposed to the normal bilayer of the other organelles) (Fujimoto and Parton, 2011).…”