Polyhydroxyalkanoate (PHA) Granules Have no Phospholipids

Bresan, Stephanie; Sznajder, Anna; Hauf, Waldemar; Forchhammer, Karl; Pfeiffer, Daniel; Jendrossek, Dieter

doi:10.1038/srep26612

Cited by 94 publications

(55 citation statements)

References 94 publications

(114 reference statements)

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“…Carbonosomes have a polymer core and a surface layer of as many as 14 proteins with different functions (13) but apparently lack a phospholipid membrane (14), in contrast to what had been assumed previously.…”

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confidence: 45%

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Absence of ppGpp Leads to Increased Mobilization of Intermediately Accumulated Poly(3-Hydroxybutyrate) in Ralstonia eutropha H16

Juengert

Borisova

Mayer

et al. 2017

Appl Environ Microbiol

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In this study, we constructed a set of Ralstonia eutropha H16 strains with single, double, or triple deletions of the (p)ppGpp synthase/hydrolase (spoT1), (p)ppGpp synthase (spoT2), and/or polyhydroxybutyrate (PHB) depolymerase (phaZa1 or phaZa3) gene, and we determined the impact on the levels of (p)ppGpp and on accumulated PHB. Mutants with deletions of both the spoT1 and spoT2 genes were unable to synthesize detectable amounts of (p)ppGpp and accumulated only minor amounts of PHB, due to PhaZa1-mediated depolymerization of PHB. In contrast, unusually high levels of PHB were found in strains in which the (p)ppGpp concentration was increased by the overexpression of (p)ppGpp synthase (SpoT2) and the absence of (p)ppGpp hydrolase. Determination of (p)ppGpp levels in wild-type R. eutropha under different growth conditions and induction of the stringent response by amino acid analogs showed that the concentrations of (p)ppGpp during the growth phase determine the amount of PHB remaining in later growth phases by influencing the efficiency of the PHB mobilization system in stationary growth. The data reported for a previously constructed ΔspoT2 strain (C. J. Brigham, D. R. Speth, C. Rha, and A. J. Sinskey, Appl Environ Microbiol 78:8033-8044, 2012, https://doi.org/ 10.1128/AEM.01693-12) were identified as due to an experimental error in strain construction, and our results are in contrast to the previous indication that the spoT2 gene product is essential for PHB accumulation in R. eutropha. IMPORTANCE Polyhydroxybutyrate (PHB) is an important intracellular carbon and energy storage compound in many prokaryotes and helps cells survive periods of starvation and other stress conditions. Research activities in several laboratories over the past 3 decades have shown that both PHB synthase and PHB depolymerase are constitutively expressed in most PHB-accumulating bacteria, such as Ralstonia eutropha. This implies that PHB synthase and depolymerase activities must be well regulated in order to avoid a futile cycle of simultaneous PHB synthesis and PHB degradation (mobilization). Previous reports suggested that the stringent response in Rhizobium etli and R. eutropha is involved in the regulation of PHB metabolism. However, the levels of (p)ppGpp and the influence of those levels on PHB accumulation and PHB mobilization have not yet been determined for any PHB-accumulating species. In this study, we optimized a (p)ppGpp extraction procedure and a highperformance liquid chromatography-mass spectrometry (HPLC-MS)-based detection method for the quantification of (p)ppGpp in R. eutropha. This enabled us to study the relationship between the concentrations of (p)ppGpp and the accumulated levels of PHB in the wild type and in several constructed mutant strains. We show that overproduction of the alarmone (p)ppGpp correlated with reduced growth and mas-

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confidence: 45%

“…PHB granules were visualized by fluorescence microscopy of Nile red-stained cells using standard filters (excitation wavelengths, 562 and 40 nm; emission wavelength, 594 nm [long-pass filter]) as described previously (13,14). Insoluble inclusions could also be visualized by bright-field microscopy and appeared as dark spheres.…”

Section: Methodsmentioning

confidence: 99%

Absence of ppGpp Leads to Increased Mobilization of Intermediately Accumulated Poly(3-Hydroxybutyrate) in Ralstonia eutropha H16

Juengert

Borisova

Mayer

et al. 2017

Appl Environ Microbiol

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“…Native PHA granules are subcellular structures formed by a polymeric core surrounded by granule-associated proteins (GAPs) (18). Microbial PHA preparations usually contain adsorbed phospholipids as well (19), although the actual occurrence of this coating in vivo has been recently questioned and might represent a purification artifact from the cell extracts (20)(21)(22). Phasins, the main component of GAPs, have a relevant role in the PHA intracellular metabolism, participating in events that include the control of the size, number, and localization of granules in the cell (23,24).…”

Section: Importancementioning

confidence: 99%

Poly-3-Hydroxybutyrate Functionalization with BioF-Tagged Recombinant Proteins

Bello-Gil

Maestro

Fonseca

et al. 2018

Appl Environ Microbiol

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Polyhydroxyalkanoates (PHAs) are biodegradable polyesters that accumulate in the cytoplasm of certain bacteria. One promising biotechnological application utilizes these biopolymers as supports for protein immobilization. Here, the PHA-binding domain of the KT2440 PhaF phasin (BioF polypeptide) was investigated as an affinity tag for the functionalization of poly-3-hydroxybutyrate (PHB) particles with recombinant proteins, namely, full-length PhaF and two fusion proteins tagged to BioF (BioF-C-LytA and BioF-β-galactosidase, containing the choline-binding module C-LytA and the β-galactosidase enzyme, respectively). The protein-biopolyester interaction was strong and stable at a wide range of pHs and temperatures, and the bound protein was highly protected from self-degradation, while the binding strength could be modulated by coating with amphiphilic compounds. Finally, BioF-β-galactosidase displayed very stable enzymatic activity after several continuous activity-plus-washing cycles when immobilized in a minibioreactor. Our results demonstrate the potentialities of PHA and the BioF tag for the construction of novel bioactive materials. Our results confirm the biotechnological potential of the BioF affinity tag as a versatile tool for functionalizing PHA supports with recombinant proteins, leading to novel bioactive materials. The wide substrate range of the BioF tag presumably enables protein immobilization of virtually all natural PHAs as well as blends, copolymers, or artificial chemically modified derivatives with novel physicochemical properties. Moreover, the strength of protein adsorption may be easily modulated by varying the coating of the support, providing new perspectives for the engineering of bioactive materials that require a tight control of protein loading.

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“…For example, bacterial microcompartments, such as the carboxysome, are surrounded by a selectively-permeable protein shell (2). Storage granules also contain a surface layer of proteins (3). In addition to these discrete organelle-like structures, chromosomal loci (4)(5)(6), proteins (7,8) and lipids (9) have all been found to exhibit non-uniform localization patterns in bacteria.…”

Section: Introductionmentioning

confidence: 99%

Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation

Ladouceur

Parmar

Biedzinski

et al. 2020

Preprint

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Once described as mere "bags of enzymes", bacterial cells are in fact highly organized, with many macromolecules exhibiting non-uniform localization patterns. Yet the physical and biochemical mechanisms that govern this spatial heterogeneity remain largely unknown. Here, we identify liquid-liquid phase separation (LLPS) as a mechanism for organizing clusters of RNA polymerase (RNAP) in E. coli. Using fluorescence imaging, we show that RNAP quickly transitions from a dispersed to clustered localization pattern as cells enter log phase in nutrientrich media. RNAP clusters are sensitive to hexanediol, a chemical that dissolves liquid-like compartments in eukaryotic cells. In addition, we find that the transcription antitermination factor NusA forms droplets in vitro and in vivo, suggesting that it may nucleate RNAP clusters. Finally, we use single-molecule tracking to characterize the dynamics of cluster components.Our results indicate that RNAP and NusA molecules move inside clusters, with mobilities faster than a DNA locus but slower than bulk diffusion through the nucleoid. We conclude that RNAP clusters are biomolecular condensates that assemble through LLPS. This work provides direct evidence for LLPS in bacteria and suggests that this process serves as a universal mechanism for intracellular organization across the tree of life. SignificanceBacterial cells are small and were long thought to have little to no internal structure. However, advances in microscopy have revealed that bacteria do indeed contain subcellular compartments. But how these compartments form has remained a mystery. Recent progress in larger, more complex eukaryotic cells has identified a novel mechanism for intracellular organization known as liquid-liquid phase separation. This process causes certain types of molecules to concentrate within distinct compartments inside the cell. Here, we demonstrate that the same process also occurs in bacteria. This work, together with a growing body of literature, suggests that liquidliquid phase separation is a universal mechanism for intracellular organization that extends across the tree of life.

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Polyhydroxyalkanoate (PHA) Granules Have no Phospholipids

Cited by 94 publications

References 94 publications

Absence of ppGpp Leads to Increased Mobilization of Intermediately Accumulated Poly(3-Hydroxybutyrate) in Ralstonia eutropha H16

Absence of ppGpp Leads to Increased Mobilization of Intermediately Accumulated Poly(3-Hydroxybutyrate) in Ralstonia eutropha H16

Poly-3-Hydroxybutyrate Functionalization with BioF-Tagged Recombinant Proteins

Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation

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