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Brittany J Belin - One of the best experts on this subject based on the ideXlab platform.
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extended hopanoid loss reduces bacterial motility and surface attachment and leads to heterogeneity in root nodule growth kinetics in a bradyrhizobium aeschynomene symbiosis
Molecular Plant-microbe Interactions, 2019Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Roughly 10% of bacteria contain genes involved in hopanoid biosynthesis, and these genes are particularly conserved in plant-associated organisms. We previously found that the extended class of Hopanoids (C35) in the nitrogen-fixing soil bacterium Bradyrhizobium diazoefficiens promotes its root nodule symbiosis with the tropical legume Aeschynomene afraspera. By quantitatively modeling root nodule development, we identify independent consequences of extended hopanoid loss in the initiation of root nodule formation and in the rate of root nodule maturation. In vitro studies demonstrate that extended Hopanoids support B. diazoefficiens motility and surface attachment, which may correlate with stable root colonization in planta. Confocal microscopy of maturing root nodules reveals that root nodules infected with extended hopanoid-deficient B. diazoefficiens contain unusually low densities of bacterial symbionts, indicating that extended Hopanoids are necessary for persistent, high levels of host infection.
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extended hopanoid loss reduces bacterial motility and surface attachment and leads to heterogeneity in root nodule growth kinetics in a bradyrhizobium aeschynomene symbiosis
Molecular Plant-microbe Interactions, 2019Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Hopanoid biosynthesis genes are conserved in nitrogen-fixing plant symbionts, and we previously found that the extended (C35) class of Hopanoids in Bradyrhizobium diazoefficiens are required for efficient symbiotic nitrogen fixation in the tropical legume host Aeschynomene afraspera. Here, we demonstrate that the nitrogen-fixation defect conferred by extended hopanoid loss can be fully explained by a reduction in root nodule sizes rather than per-bacteroid nitrogen-fixation levels. Using a single-nodule tracking approach to quantify A. afraspera nodule development, we provide a quantitative model of root nodule development in this host, uncovering both the baseline growth parameters for wild-type nodules and a surprising heterogeneity of extended hopanoid mutant developmental phenotypes. These phenotypes include a delay in root nodule initiation and the presence of a subpopulation of nodules with slow growth rates and low final volumes, which are correlated with reduced motility and surface attachment in vitro and lower bacteroid densities in planta, respectively. This work provides a quantitative reference point for understanding the phenotypic diversity of ineffective symbionts in A. afraspera and identifies specific developmental stages affected by extended hopanoid loss for future mechanistic work.
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extended hopanoid loss reduces bacterial motility and surface attachment and leads to heterogeneity in root nodule growth kinetics in a bradyrhizobium aeschynomene symbiosis
bioRxiv, 2018Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Abstract Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Hopanoid biosynthesis genes are conserved in nitrogen-fixing plant symbionts, and we previously found that the extended (C35) class of Hopanoids in Bradyrhizobium diazoefficiens are required for efficient symbiotic nitrogen fixation in the tropical legume host Aeschynomene afraspera. Here we demonstrate that the nitrogen fixation defect conferred by extended loss can fully be explained by a reduction in root nodule sizes rather than per-bacteroid nitrogen fixation levels. Using a single-nodule tracking approach to track A. afraspera nodule development, we provide a quantitative model of root nodule development in this host, uncovering both the baseline growth parameters for wild-type nodules and a surprising heterogeneity of extended hopanoid mutant developmental phenotypes. These phenotypes include a delay in root nodule initiation and presence of a subpopulation of nodules with slow growth rates and low final volumes, which are correlated with reduced motility and surface attachment in vitro and lower bacteroid densities in planta, respectively. This work provides a quantitative reference point for understanding the phenotypic diversity of ineffective symbionts in A. afraspera and identifies specific developmental stages affected by extended hopanoid loss for future mechanistic work.
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extended hopanoid lipids promote bacterial motility surface attachment and root nodule development in the bradyrhizobium diazoefficiens aeschynomene afraspera symbiosis
bioRxiv, 2018Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Roughly 10% of bacteria contain genes involved in hopanoid biosynthesis, and these genes are particularly conserved in plant-associated organisms. We previously found that the extended class of Hopanoids (C35) in the nitrogen-fixing soil bacterium Bradyrhizobium diazoefficiens promotes its root nodule symbiosis with the tropical legume Aeschynomene afraspera. By quantitatively modeling root nodule development, we identify independent roles for Hopanoids in the initiation of root nodule formation and in determining the rate of root nodule maturation. In vitro studies demonstrate that extended Hopanoids support B. diazoefficiens motility and surface attachment, which may correlate with stable root colonization in planta. Confocal microscopy of maturing root nodules reveals that root nodules infected with extended hopanoid-deficient B. diazoefficiens contain unusually low densities of bacterial symbionts, indicating that extended Hopanoids are necessary for persistent, high levels of host infection. This work identifies extended Hopanoids as regulators of the efficiency of Bradyrhizobia nitrogen-fixing symbioses, agriculturally and economically significant associations with growing importance in a changing climate.
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hopanoid lipids from membranes to plant bacteria interactions
Nature Reviews Microbiology, 2018Co-Authors: Brittany J Belin, Nicolas Busset, Antonio Molinaro, Eric Giraud, Alba SilipoAbstract:Lipid research represents a frontier for microbiology, as showcased by hopanoid lipids. Hopanoids, which resemble sterols and are found in the membranes of diverse bacteria, have left an extensive molecular fossil record. They were first discovered by petroleum geologists. Today, hopanoid-producing bacteria remain abundant in various ecosystems, such as the rhizosphere. Recently, great progress has been made in our understanding of hopanoid biosynthesis, facilitated in part by technical advances in lipid identification and quantification. A variety of genetically tractable, hopanoid-producing bacteria have been cultured, and tools to manipulate hopanoid biosynthesis and detect Hopanoids are improving. However, we still have much to learn regarding how hopanoid production is regulated, how Hopanoids act biophysically and biochemically, and how their production affects bacterial interactions with other organisms, such as plants. The study of Hopanoids thus offers rich opportunities for discovery.
Gerard C L Wong - One of the best experts on this subject based on the ideXlab platform.
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extended hopanoid loss reduces bacterial motility and surface attachment and leads to heterogeneity in root nodule growth kinetics in a bradyrhizobium aeschynomene symbiosis
Molecular Plant-microbe Interactions, 2019Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Roughly 10% of bacteria contain genes involved in hopanoid biosynthesis, and these genes are particularly conserved in plant-associated organisms. We previously found that the extended class of Hopanoids (C35) in the nitrogen-fixing soil bacterium Bradyrhizobium diazoefficiens promotes its root nodule symbiosis with the tropical legume Aeschynomene afraspera. By quantitatively modeling root nodule development, we identify independent consequences of extended hopanoid loss in the initiation of root nodule formation and in the rate of root nodule maturation. In vitro studies demonstrate that extended Hopanoids support B. diazoefficiens motility and surface attachment, which may correlate with stable root colonization in planta. Confocal microscopy of maturing root nodules reveals that root nodules infected with extended hopanoid-deficient B. diazoefficiens contain unusually low densities of bacterial symbionts, indicating that extended Hopanoids are necessary for persistent, high levels of host infection.
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extended hopanoid loss reduces bacterial motility and surface attachment and leads to heterogeneity in root nodule growth kinetics in a bradyrhizobium aeschynomene symbiosis
Molecular Plant-microbe Interactions, 2019Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Hopanoid biosynthesis genes are conserved in nitrogen-fixing plant symbionts, and we previously found that the extended (C35) class of Hopanoids in Bradyrhizobium diazoefficiens are required for efficient symbiotic nitrogen fixation in the tropical legume host Aeschynomene afraspera. Here, we demonstrate that the nitrogen-fixation defect conferred by extended hopanoid loss can be fully explained by a reduction in root nodule sizes rather than per-bacteroid nitrogen-fixation levels. Using a single-nodule tracking approach to quantify A. afraspera nodule development, we provide a quantitative model of root nodule development in this host, uncovering both the baseline growth parameters for wild-type nodules and a surprising heterogeneity of extended hopanoid mutant developmental phenotypes. These phenotypes include a delay in root nodule initiation and the presence of a subpopulation of nodules with slow growth rates and low final volumes, which are correlated with reduced motility and surface attachment in vitro and lower bacteroid densities in planta, respectively. This work provides a quantitative reference point for understanding the phenotypic diversity of ineffective symbionts in A. afraspera and identifies specific developmental stages affected by extended hopanoid loss for future mechanistic work.
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extended hopanoid loss reduces bacterial motility and surface attachment and leads to heterogeneity in root nodule growth kinetics in a bradyrhizobium aeschynomene symbiosis
bioRxiv, 2018Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Abstract Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Hopanoid biosynthesis genes are conserved in nitrogen-fixing plant symbionts, and we previously found that the extended (C35) class of Hopanoids in Bradyrhizobium diazoefficiens are required for efficient symbiotic nitrogen fixation in the tropical legume host Aeschynomene afraspera. Here we demonstrate that the nitrogen fixation defect conferred by extended loss can fully be explained by a reduction in root nodule sizes rather than per-bacteroid nitrogen fixation levels. Using a single-nodule tracking approach to track A. afraspera nodule development, we provide a quantitative model of root nodule development in this host, uncovering both the baseline growth parameters for wild-type nodules and a surprising heterogeneity of extended hopanoid mutant developmental phenotypes. These phenotypes include a delay in root nodule initiation and presence of a subpopulation of nodules with slow growth rates and low final volumes, which are correlated with reduced motility and surface attachment in vitro and lower bacteroid densities in planta, respectively. This work provides a quantitative reference point for understanding the phenotypic diversity of ineffective symbionts in A. afraspera and identifies specific developmental stages affected by extended hopanoid loss for future mechanistic work.
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extended hopanoid lipids promote bacterial motility surface attachment and root nodule development in the bradyrhizobium diazoefficiens aeschynomene afraspera symbiosis
bioRxiv, 2018Co-Authors: Brittany J Belin, E T Tookmanian, J De Anda, Gerard C L WongAbstract:Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Roughly 10% of bacteria contain genes involved in hopanoid biosynthesis, and these genes are particularly conserved in plant-associated organisms. We previously found that the extended class of Hopanoids (C35) in the nitrogen-fixing soil bacterium Bradyrhizobium diazoefficiens promotes its root nodule symbiosis with the tropical legume Aeschynomene afraspera. By quantitatively modeling root nodule development, we identify independent roles for Hopanoids in the initiation of root nodule formation and in determining the rate of root nodule maturation. In vitro studies demonstrate that extended Hopanoids support B. diazoefficiens motility and surface attachment, which may correlate with stable root colonization in planta. Confocal microscopy of maturing root nodules reveals that root nodules infected with extended hopanoid-deficient B. diazoefficiens contain unusually low densities of bacterial symbionts, indicating that extended Hopanoids are necessary for persistent, high levels of host infection. This work identifies extended Hopanoids as regulators of the efficiency of Bradyrhizobia nitrogen-fixing symbioses, agriculturally and economically significant associations with growing importance in a changing climate.
Dianne K Newman - One of the best experts on this subject based on the ideXlab platform.
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Hopanoids play a role in stress tolerance and nutrient storage in the cyanobacterium nostoc punctiforme
Geobiology, 2017Co-Authors: Jessica Ricci, Dianne K Newman, R Morton, Gargi Kulkarni, M L SummersAbstract:Hopanes are abundant in ancient sedimentary rocks at discrete intervals in Earth history, yet interpreting their significance in the geologic record is complicated by our incomplete knowledge of what their progenitors, Hopanoids, do in modern cells. To date, few studies have addressed the breadth of diversity of physiological functions of these lipids and whether those functions are conserved across the hopanoid-producing bacterial phyla. Here, we generated mutants in the filamentous cyanobacterium, Nostoc punctiforme, that are unable to make all Hopanoids (shc) or 2-methylHopanoids (hpnP). While the absence of Hopanoids impedes growth of vegetative cells at high temperature, the shc mutant grows faster at low temperature. This finding is consistent with Hopanoids acting as membrane rigidifiers, a function shared by other hopanoid-producing phyla. Apart from impacting fitness under temperature stress, Hopanoids are dispensable for vegetative cells under other stress conditions. However, Hopanoids are required for stress tolerance in akinetes, a resting survival cell type. While 2-methylated Hopanoids do not appear to contribute to any stress phenotype, total Hopanoids and to a lesser extent 2-methylHopanoids were found to promote the formation of cyanophycin granules in akinetes. Finally, although Hopanoids support symbiotic interactions between Alphaproteobacteria and plants, they do not appear to facilitate symbiosis between N. punctiforme and the hornwort Anthoceros punctatus. Collectively, these findings support interpreting hopanes as general environmental stress biomarkers. If hopanoid-mediated enhancement of nitrogen-rich storage products turns out to be a conserved phenomenon in other organisms, a better understanding of this relationship may help us parse the enrichment of 2-methylhopanes in the rock record during episodes of disrupted nutrient cycling.
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Specific hopanoid classes differentially affect free-living and symbiotic states of Bradyrhizobium diazoefficiens
mBio, 2015Co-Authors: Gargi Kulkarni, Alba Silipo, Clémence Chaintreuil, Daniel Gargani, Nicolas Busset, Antonio Molinaro, Eric Giraud, Dianne K NewmanAbstract:A better understanding of how bacteria resist stresses encountered during the progression of plant-microbe symbioses will advance our ability to stimulate plant growth. Here, we show that the symbiotic system comprising the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens and the legume Aeschynomene afraspera requires hopanoid production for optimal fitness. While methylated (2Me) Hopanoids contribute to growth under plant-cell-like microaerobic and acidic conditions in the free-living state, they are dispensable during symbiosis. In contrast, synthesis of extended (C-35) Hopanoids is required for growth microaerobically and under various stress conditions (high temperature, low pH, high osmolarity, bile salts, oxidative stress, and antimicrobial peptides) in the free-living state and also during symbiosis. These defects might be due to a less rigid membrane resulting from the absence of free or lipidA-bound C-35 Hopanoids or the accumulation of the C-35 hopanoid diploptene. Our results also show that C-35 Hopanoids are necessary for symbiosis only with the host Aeschynomene afraspera but not with soybean. This difference is likely related to the presence of cysteine-rich antimicrobial peptides in Aeschynomene nodules that induce drastic modification in bacterial morphology and physiology. The study of hopanoid mutants in plant symbionts thus provides an opportunity to gain insight into host-microbe interactions during later stages of symbiotic progression, as well as the microenvironmental conditions for which Hopanoids provide a fitness advantage. IMPORTANCE Because bradyrhizobia provide fixed nitrogen to plants, this work has potential agronomical implications. An understanding of how Hopanoids facilitate bacterial survival in soils and plant hosts may aid the engineering of more robust agronomic strains, especially relevant in regions that are becoming warmer and saline due to climate change. Moreover, this work has geobiological relevance: hopanes, molecular fossils of Hopanoids, are enriched in ancient sedimentary rocks at discrete intervals in Earth history. This is the first study to uncover roles for 2Me- and C-35 Hopanoids in the context of an ecological niche that captures many of the stressful environmental conditions thought to be important during (2Me)-hopane deposition. Though much remains to be done to determine whether the conditions present within the plant host are shared with niches of relevance to the rock record, our findings represent an important step toward identifying conserved mechanisms whereby Hopanoids contribute to fitness.
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2 methylHopanoids are maximally produced in akinetes of nostoc punctiforme geobiological implications
Geobiology, 2009Co-Authors: David M Doughty, Ryan C Hunter, Roger E Summons, Dianne K NewmanAbstract:2-Methylhopanes, molecular fossils of 2-methylbacteriohopanepolyol (2-MeBHP) lipids, have been proposed as biomarkers for cyanobacteria, and by extension, oxygenic photosynthesis. However, the robustness of this interpretation is unclear, as 2-methylHopanoids occur in organisms besides cyanobacteria and their physiological functions are unknown. As a first step toward understanding the role of 2-MeBHP in cyanobacteria, we examined the expression and intercellular localization of Hopanoids in the three cell types of Nostoc punctiforme: vegetative cells, akinetes, and heterocysts. Cultures in which N. punctiforme had differentiated into akinetes contained approximately 10-fold higher concentrations of 2-methylHopanoids than did cultures that contained only vegetative cells. In contrast, 2-methylHopanoids were only present at very low concentrations in heterocysts. Hopanoid production initially increased threefold in cells starved of nitrogen but returned to levels consistent with vegetative cells within 2 weeks. Vegetative and akinete cell types were separated into cytoplasmic, thylakoid, and outer membrane fractions; the increase in hopanoid expression observed in akinetes was due to a 34-fold enrichment of hopanoid content in their outer membrane relative to vegetative cells. Akinetes formed in response either to low light or phosphorus limitation, exhibited the same 2-methylhopanoid localization and concentration, demonstrating that 2-methylHopanoids are associated with the akinete cell type per se. Because akinetes are resting cells that are not photosynthetically active, 2-methylHopanoids cannot be functionally linked to oxygenic photosynthesis in N. punctiforme.
Natalia Wilke - One of the best experts on this subject based on the ideXlab platform.
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hopanoid hopene locates in the interior of membranes and affects their properties
Langmuir, 2021Co-Authors: Matias A Crosio, Dayane S Alvares, Natalia WilkeAbstract:Hopanoids are proposed as sterol surrogates in some bacteria, and it has been proved that some Hopanoids are able to induce a liquid-order phase state in lipid membranes. The members of this group of molecules have diverse structures, and not all of them have been studied in detail yet. Here, we study membranes with the hopanoid hopene (hop-22 (29)-ene or diploptene), which is the product of the cycling of squalene by squalene-hopene cyclase, and thus is present in the first step of hopanoid biosynthesis. Hopene is particularly interesting because it lacks a polar head group, which opens the question of how does this molecule accommodate in a lipid membrane, and what are the effects promoted by its presence. In order to get an insight into this, we prepared monolayers and bilayers of a phospholipid with hopene and studied their properties in comparison with pure phospholipid membranes, and with the sterol cholesterol or the hopanoid diplopterol. Film stiffness, shear viscosity, and bending dynamics were very affected by the presence of hopene, while zeta-potential, generalized polarization of Laurdan, and conductivity were affected moderately by this molecule. The results suggest that at very low percentages, hopene locates parallel to the phospholipid molecules, while the excess of the hopene molecules stays between leaflets, as previously proposed using molecular dynamics simulations.
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the antimicrobial peptide polybia mp1 differentiates membranes with the hopanoid diplopterol from those with cholesterol
BBA Advances, 2021Co-Authors: Mariela R Monti, Joao Ruggiero Neto, Dayane S Alvares, Natalia WilkeAbstract:Abstract Polybia-MP1 is an antimicrobial peptide that shows a decreased activity in membranes with cholesterol (CHO). Since it is now accepted that Hopanoids act as sterol-surrogates in some sterol-lacking bacteria, we here inquire about the impact of Polybia-MP1 on membranes containing the hopanoid diplopterol (DP) in comparison to membranes with CHO. We found that, despite the properties induced on lipid membranes by DP are similar to those induced by CHO, the effect of Polybia-MP1 on membranes with CHO or DP was significantly different. DP did not prevent dye release from LUVs, nor the insertion of Polybia-MP1 into monolayers, and peptide-membrane affinity was higher for those with DP than with CHO. Zeta potentials ( ζ ) for DP-containing LUVs showed a complex behavior at increasing peptide concentration. The effect of the peptide on membrane elasticity, investigated by nanotube retraction experiments, showed that peptide addition softened all membrane compositions, but membranes with DP got stiffer at long times. Considering this, and the ζ results, we propose that peptides accumulate at the interface adopting different arrangements, leading to a non-monotonic behavior. Possible correlations with cell membranes were inquired testing the antimicrobial activity of Polybia-MP1 against hopanoid-lacking bacteria pre-incubated with DP or CHO. The fraction of surviving cells was lower in cultures incubated with DP compared to those incubated with CHO. We propose that the higher activity of Polybia-MP1 against some bacteria compared to mammalian cells is not only related to membrane electrostatics, but also the composition of neutral lipids, particularly the Hopanoids, could be important.
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Hopanoids like sterols modulate dynamics compaction phase segregation and permeability of membranes
Biochimica et Biophysica Acta, 2019Co-Authors: Agustin Mangiarotti, Dario M Genovese, Christoph A Naumann, Mariela R Monti, Natalia WilkeAbstract:Abstract In recent years, Hopanoids, a group of pentacyclic compounds found in bacterial membranes, are in the spotlight since it was proposed that they induce order in lipid membranes in a similar way cholesterol do in eukaryotes, despite their structural differences. We studied here whether diplopterol (an abundant hopanoid) promoted similar effects on model membranes as sterols do. We analyzed the compaction, dynamics, phase segregation, permeability and compressibility of model membranes containing diplopterol, and compared with those containing sterols from animals, plants and fungi. We also tested the effect that the incubation with diplopterol had on hopanoid-lacking bacteria. Our results show that diplopterol induces phase segregation, increases lipid compaction, and decreases permeability on phospholipid membranes, while retaining membrane fluidity and compressibility. Furthermore, the exposition to this hopanoid decreases the permeability of the opportunistic pathogen Pseudomonas aeruginosa and increases the resistance to antibiotics. All effects promoted by diplopterol were similar to those generated by the sterols. Our observations add information on the functional significance of Hopanoids as molecules that play an important role in membrane organization and dynamics in model membranes and in a bacterial system.
Miguel A Valvano - One of the best experts on this subject based on the ideXlab platform.
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elucidation of the burkholderia cenocepacia hopanoid biosynthesis pathway uncovers functions for conserved proteins in hopanoid producing bacteria
Environmental Microbiology, 2015Co-Authors: Crystal L Schmerk, Paula V Welander, Mohamad A Hamad, Katie Bain, Mark A Bernards, Miguel A ValvanoAbstract:Summary Hopanoids are bacterial surrogates of eukaryotic membrane sterols and among earth's most abundant natural products. Their molecular fossils remain in sediments spanning more than a billion years. However, hopanoid metabolism and function are not fully understood. Burkholderia species are environmental opportunistic pathogens that produce Hopanoids and also occupy diverse ecological niches. We investigated Hopanoids biosynthesis in Burkholderia cenocepacia by deletion mutagenesis and structural characterization of the Hopanoids produced by the mutants. The enzymes encoded by hpnH and hpnG were essential for production of all C35 extended Hopanoids, including bacteriohopanetetrol (BHT), BHT glucosamine and BHT cyclitol ether. Deletion of hpnI resulted in BHT production, while ΔhpnJ produced only BHT glucosamine. Thus, HpnI is required for BHT glucosamine production while HpnJ is responsible for its conversion to the cyclitol ether. The ΔhpnH and ΔhpnG mutants could not grow under any stress condition tested, whereas ΔhpnI, ΔhpnJ and ΔhpnK displayed wild-type growth rates when exposed to detergent, but varying levels of sensitivity to low pH and polymyxin B. This study not only elucidates the biosynthetic pathway of Hopanoids in B. cenocepacia, but also uncovers a biosynthetic role for the conserved proteins HpnI, HpnJ and HpnK in other hopanoid-producing bacteria.
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hopanoid production is required for low ph tolerance antimicrobial resistance and motility in burkholderia cenocepacia
Journal of Bacteriology, 2011Co-Authors: Crystal L Schmerk, Mark A Bernards, Miguel A ValvanoAbstract:Hopanoids are pentacyclic triterpenoids that are thought to be bacterial surrogates for eukaryotic sterols, such as cholesterol, acting to stabilize membranes and to regulate their fluidity and permeability. To date, very few studies have evaluated the role of Hopanoids in bacterial physiology. The synthesis of Hopanoids depends on the enzyme squalene-hopene cyclase (Shc), which converts the linear squalene into the basic hopene structure. Deletion of the 2 genes encoding Shc enzymes in Burkholderia cenocepacia K56-2, BCAM2831 and BCAS0167, resulted in a strain that was unable to produce Hopanoids, as demonstrated by gas chromatography and mass spectrometry. Complementation of the Δshc mutant with only BCAM2831 was sufficient to restore hopanoid production to wild-type levels, while introducing a copy of BCAS0167 alone into the Δshc mutant produced only very small amounts of the hopanoid peak. The Δshc mutant grew as well as the wild type in medium buffered to pH 7 and demonstrated no defect in its ability to survive and replicate within macrophages, despite transmission electron microscopy (TEM) revealing defects in the organization of the cell envelope. The Δshc mutant displayed increased sensitivity to low pH, detergent, and various antibiotics, including polymyxin B and erythromycin. Loss of hopanoid production also resulted in severe defects in both swimming and swarming motility. This suggests that hopanoid production plays an important role in the physiology of B. cenocepacia.