Lipid composition of multilamellar bodies secreted by Dictyostelium discoideum reveals their amoebal origin

Control of giant vesicle assemblies by stimuli-responsive lipids

We describe a bottom-up synthesis of giant vesicles (GVs) utilizing an artificial stimuli-responsive diazobenzene lipid building block. Controlled by light, the GVs can exhibit dynamic behaviors, including reversible formation, the generation of highly multilamellar assemblies, and vesicle capturing and releasing events.

Lipidomics Analysis of Multilamellar Bodies Produced by Amoeba Acanthamoeba castellanii in Co-Culture with Klebsiella aerogenes

Multilamellar bodies (MLBs) are membrane-bound cytoplasmic organelles of lysosomal origin. In some protozoa, they were considered as lipid storage secretory organelles and feasible participants in cell-to-cell communication. However, for Acanthamoeba castellanii, similar vesicles were indicated only as possible transmission vectors of several pathogenic bacteria without attributing them biological roles and activities. Since amoebae belonging to the genus Acanthamoeba are not only of environmental but also of clinical significance, it is of great importance to fully understand their physiology. Thus, determination of MLB lipid composition could partly address these questions. Because MLBs are secreted by amoebae as a result of bacteria digestion, the co-culture technique with the use of “edible” Klebsiella aerogenes was used for their production. Lipids obtained from The MLB fraction, previously purified from bacterial debris, were analyzed by high-performance thin-layer chromatography, gas chromatography coupled with mass spectrometry, and high-resolution mass spectrometry. Lipidomic analysis revealed that in MLBs, a very abundant lipid class was a non-phosphorous, polar glycerolipids, diacylglyceryl-O-(N,N,N)-trimethylhomoserine (DGTS). Since DGTSs are regarded as a source of nitrogen and fatty acids, MLBs can be considered as lipid storage organelles produced in stress conditions. Further, the identification of phytoceramides and possible new betaine derivatives indicates that MLBs might have a distinct bioactive potential.

Aeromonas salmonicida intra-species divergence revealed by the various strategies displayed when grazed by Tetrahymena pyriformis

Worldwide, Aeromonas salmonicida is a major bacterial pathogen of fish in both marine and freshwater environments. Despite psychrophilic growth being common for this species, the number of characterized mesophilic strains is increasing. Thus, this species may serve as a model for the study of intraspecies lifestyle diversity. Although bacteria are preyed upon by protozoan predators, their interaction inside or outside the phagocytic pathway of the predator can provide several advantages to the bacteria. To correlate intraspecies diversity with predation outcome, we studied the fate of psychrophilic and mesophilic strains of A. salmonicida co-cultured with the ciliate Tetrahymena pyriformis. Three types of outcome were observed: digestion, resistance to phagocytosis and pathogenicity. The psychrophilic strains are fully digested by the ciliate. In contrast, the mesophilic A. salmonicida subsp. pectinolytica strain is pathogenic to the ciliate. All the other mesophilic strains display mechanisms to resist phagocytosis and/or digestion, which allow them to survive ciliate predation. In some cases, passage through the phagocytic pathway resulted in a few mesophilic A. salmonicida being packaged inside fecal pellets. This study sheds light on the great phenotypic diversity observed in the complex range of mechanisms used by A. salmonicida to confront a predator.

Microfluidic technologies for the synthesis and manipulation of biomimetic membranous nano-assemblies

Microfluidics has been proposed as an attractive alternative to conventional bulk methods used in the generation of self-assembled biomimetic structures, particularly where there is a desire for more scalable production. The approach also allows for greater control over the self-assembly process, and parameters such as particle architecture, size, and composition can be finely tuned. Microfluidic techniques used in the generation of microscale assemblies (giant vesicles and higher-order multi-compartment assemblies) are fairly well established. These tend to rely on microdroplet templation, and the resulting structures have found use as comparmentalised motifs in artificial cells. Challenges in generating sub-micron droplets have meant that reconfiguring this approach to form nano-scale structures is not straightforward. This is beginning to change however, and recent technological advances have instigated the manufacture and manipulation of an increasingly diverse repertoire of biomimetic nano-assemblies, including liposomes, polymersomes, hybrid particles, multi-lamellar structures, cubosomes, hexosomes, nanodiscs, and virus-like particles. The following review will discuss these higher-order self-assembled nanostructures, including their biochemical and industrial applications, and techniques used in their production and analysis. We suggest ways in which existing technologies could be repurposed for the enhanced design, manufacture, and exploitation of these structures and discuss potential challenges and future research directions. By compiling recent advances in this area, it is hoped we will inspire future efforts toward establishing scalable microfluidic platforms for the generation of biomimetic nanoparticles of enhanced architectural and functional complexity.

Marine Bacteria Display Different Escape Mechanisms When Facing Their Protozoan Predators

Free-living amoeba are members of microbial communities such as biofilms in terrestrial, fresh, and marine habitats. Although they are known to live in close association with bacteria in many ecosystems such as biofilms, they are considered to be major bacterial predators in many ecosystems. Little is known on the relationship between protozoa and marine bacteria in microbial communities, more precisely on how bacteria are able survive in environmental niches where these bacterial grazers also live. The objective of this work is to study the interaction between the axenized ubiquitous amoeba Acanthamoeba castellanii and four marine bacteria isolated from immersed biofilm, in order to evaluate if they would be all grazed upon by amoeba or if they would be able to survive in the presence of their predator. At a low bacteria-to-amoeba ratio, we show that each bacterium is phagocytized and follows a singular intracellular path within this host cell, which appears to delay or to prevent bacterial digestion. In particular, one of the bacteria was found in the amoeba nucleolar compartment whereas another strain was expelled from the amoeba in vesicles. We then looked at the fate of the bacteria grown in a higher bacteria-to-amoeba ratio, as a preformed mono- or multi-species biofilm in the presence of A. castellanii. We show that all biofilms were subjected to detachment from the surface in the presence of the amoeba or its supernatant. Overall, these results show that bacteria, when facing the same predator, exhibit a variety of escape mechanisms at the cellular and population level, when we could have expected a simple bacterial grazing. Therefore, this study unravels new insights into the survival of environmental bacteria when facing predators that they could encounter in the same microbial communities.

Morphology and Ecology of Two New Amoebae, Isolated From a Thalassohaline Lake, Dziani Dzaha

Dziani Dzaha is a hypersaline lake (Mayotte island), whose microbial community is dominated by photosynthetic microorganisms. Here, we describe two new free-living heteroloboseans. One belonging to the Pharyngomonas genus and the other, whose 18S rRNA gene sequence shares only 85% homology to its closest relatives Euplaesiobystra hypersalinica, was proposed as a new species of this genus being called Euplaesiobystra dzianiensis. Both strains were salt tolerant to 75‰ and grew between 25 and 37°C. Their distribution patterns varied seasonally and depended also on depth. Noticeably, both free-living amoebae isolates were able to graze on Arthrospira filaments, which are found within the same water layer. In conclusion, we document for the first time the presence and ecology of free-living amoebae in the thalassohaline lake Dziani Dzaha, and describe a new species of the Euplaesiobystra genus.

Evidence that Bacteria Packaging by Tetrahymena Is a Widespread Phenomenon

Protozoa are natural predators of bacteria, but some bacteria can evade digestion once phagocytosed. Some of these resistant bacteria can be packaged in the fecal pellets produced by protozoa, protecting them from physical stresses and biocides. Depending on the bacteria and protozoa involved in the packaging process, pellets can have different morphologies. In the present descriptive study, we evaluated the packaging process with 20 bacteria that have never been tested before for packaging by ciliates. These bacteria have various characteristics (shape, size, Gram staining). All of them appear to be included in pellets produced by the ciliates Tetrahymena pyriformis and/or T. thermophila in at least one condition tested. We then focused on the packaging morphology of four of these bacteria. Our results demonstrated that, as shown previously for Mycobacterium smegmatis, the packaging of Microbacterium oxydans, Micrococcus luteus, and Cupriavidus sp. was formed of a single layer of material. The packaging of Cellulosimicrobiumfunkei was made of indistinguishable material. A different pellet morphology was obtained for each of the four bacterial strains studied. The ingestion of small bacteria resulted in rounder, denser, and more regular pellets. These results support the idea that bacteria packaging is a relatively widespread phenomenon.

Various dictyostelids from the environment can produce multilamellar bodies

Multilamellar bodies (MLBs), structures composed of concentric membrane layers, are known to be produced by different protozoa, including species of ciliates, free-living amoebae, and Dictyostelium discoideum social amoebae. Initially believed to be metabolic waste, potential roles like cell communication and food storage have been suggested for D. discoideum MLBs, which could be useful for the multicellular development of social amoebae and as a food source. However, among dictyostelids, this phenomenon has only been observed with D. discoideum, and mainly with laboratory strains grown in axenic conditions. It was thought that other social amoebae may also produce MLBs. Four environmental social amoeba isolates were characterized. All strains belong to the Dictyostelium genus, including some likely to be Dictyostelium giganteum. They have distinctive phenotypes comprising their growth rate on Klebsiella aerogenes lawns and the morphology of their fruiting bodies. They all produce MLBs like those produced by a D. discoideum laboratory strain when grown on K. aerogenes lawns, as revealed by analysis using the H36 antibody in epifluorescence microscopy as well as by transmission electron microscopy. Consequently, this study shows that MLBs are produced by various dictyostelid species, which further supports a role for MLBs in the lifestyle of amoebae.

Symbiont location, host fitness, and possible coadaptation in a symbiosis between social amoebae and bacteria

Recent symbioses, particularly facultative ones, are well suited for unravelling the evolutionary give and take between partners. Here we look at variation in natural isolates of the social amoeba Dictyostelium discoideum and their relationships with bacterial symbionts, Burkholderia hayleyella and Burkholderia agricolaris. Only about a third of field-collected amoebae carry a symbiont. We cured and cross-infected amoebae hosts with different symbiont association histories and then compared host responses to each symbiont type. Before curing, field-collected clones did not vary significantly in overall fitness, but infected hosts produced morphologically different multicellular structures. After curing and reinfecting, host fitness declined. However, natural B. hayleyella hosts suffered fewer fitness costs when reinfected with B. hayleyella, indicating that they have evolved mechanisms to tolerate their symbiont. Our work suggests that amoebae hosts have evolved mechanisms to tolerate specific acquired symbionts; exploring host-symbiont relationships that vary within species may provide further insights into disease dynamics.

Resin secretory canals in Protium heptaphyllum (Aubl.) Marchand. (Burseraceae): a tridimensional branched and anastomosed system

Protium heptaphyllum is a Burseraceae species known by the production of aromatic resin with medicinal, economic, and ecological values. Information on the development, architecture, and lifetime of the secretory system are crucial to understand the resin production and contribute to a more sustainable tapping regime. We investigated the histology and ultrastructure of the secretory canals under a developmental point of view. Stem samples were analyzed under light and transmission electron microscopy by conventional and cytochemical methods. Secretory canals, originated from procambium and cambium, occurred immersed in the primary and secondary phloem. Mature canals have a secretory epithelium and a wide lumen where the exudate is accumulated. A sheath of parenchyma cells with meristematic features surrounds the epithelium. The canals originate by schizogenesis and develop by schyzolysigenesis. Canals active in secretion occurred since the shoot apex and near the cambium. In the dilation zone of the secondary phloem, secretory canals exhibit sclerified epithelial and sheath cells and are inactive in secretion. Secreting epithelial cells have subcellular apparatus consistent with oleoresin, polysaccharides, and enzymes secretion. Pectinase and cellulase were cytochemically detected in developing canals and are involved in cell wall changes associated to canal growth and release of exudate. In P. heptaphyllum, the secretory system has a complex structure resultant from longitudinal growth, lateral ramification, and fusion of the adjacent canals, in addition to intrusive growth of both epithelial and sheath cells. Although some anatomical results are already known, ultrastructural data represent the novelty of this work. Our findings can contribute to the establishment of more efficient and sustainable techniques for resin extraction in this species.

Genomic and phenotypic characterization of an atypical Aeromonas salmonicida strain isolated from a lumpfish and producing unusual granular structures

Aeromonas salmonicida strains are roughly classified into two categories, typical and atypical strains. The latter mainly regroup isolates that present unusual phenotypes or hosts, comparatively to the typical strains that belong to the salmonicida subspecies. This study focuses on an uncharacterized atypical strain, M18076-11, isolated from lumpfish (Cyclopterus lumpus) and not part of the four recognized Aeromonas salmonicida subspecies. This isolate presents an unreported phenotype in the A. salmonicida species: the formation of large granular aggregates. Granules are formed of a heterogeneous mix of live and dead cells, with live cells composing the majority of the population. Even if no mechanism was determined to cause cellular aggregation, small globular structures at the cell surface were observed, which might affect granular formation. Pan-genome phylogenetic analysis indicated that this strain groups alongside the masoucida subspecies. However, phenotypic tests showed that these strains have diverging phenotypes, suggesting that M18076-11 might belong to a new subspecies. Also, a pAsal1-like plasmid, which was only reported in strains of the subspecies salmonicida, was discovered in M18076-11. This study sheds light on unsuspected diversity in A. salmonicida subspecies and stresses the need of thorough identification when a new strain is encountered, as unique traits might be discovered.

Packaging of Mycobacterium smegmatis bacteria into fecal pellets by the ciliate Tetrahymena pyriformis

Mycobacteria are widespread microorganisms that live in various environments, including man-made water systems where they cohabit with protozoa. Environmental mycobacterial species give rise to many opportunistic human infections and can infect phagocytic protozoa. Protozoa such as amoebae and ciliates feeding on bacteria can sometimes get rid of non-digestible or pathogenic material by packaging it into secreted fecal pellets. Usually, packaged bacteria are still viable and are protected against chemical and physical stresses. We report here that mycobacteria can be packaged into pellets by ciliates. The model bacterium Mycobacterium smegmatis survived digestion in food vacuoles of the ciliate Tetrahymena pyriformis and was included in expelled fecal pellets. LIVE/DEAD® staining confirmed that packaged M. smegmatis cells preserved their viability through the process. Scanning and transmission electron microscopy revealed that bacteria are packaged in undefined filamentous and/or laminar substances and that just a thin layer of material seemed to keep the pellet contents in a spherical shape. These results imply that packaging of bacteria is more common than expected, and merits further study to understand its role in persistence and dissemination of pathogens in the environment.

Isolation, Synthesis, and Biological Activity of Chlorinated Alkylresorcinols from Dictyostelium Cellular Slime Molds

Eight chlorinated alkylresorcinols, monochasiol A-H (1-8), were isolated from the fruiting bodies of Dictyostelium monochasioides. Compounds 1-8 were synthesized to confirm their structures and to obtain sufficient material for performing biological tests. Monochasiol A (1) selectively inhibited the concanavalin A-induced interleukin-2 production in Jurkat cells, a human T lymphocyte cell line. Monochasiols were biogenetically synthesized by the combination of biosynthetic enzymes relating to the principal polyketides, MPBD and DIF-1, produced by Dictyostelium discoideum.

Janus dendrimersomes coassembled from fluorinated, hydrogenated, and hybrid Janus dendrimers as models for cell fusion and fission

A three-component system of Janus dendrimers (JDs) including hydrogenated, fluorinated, and hybrid hydrogenated-fluorinated JDs are reported to coassemble by film hydration at specific ratios into an unprecedented class of supramolecular Janus particles (JPs) denoted Janus dendrimersomes (JDSs). They consist of a dumbbell-shaped structure composed of an onion-like hydrogenated vesicle and an onion-like fluorinated vesicle tethered together. The synthesis of dye-tagged analogs of each JD component enabled characterization of JDS architectures with confocal fluorescence microscopy. Additionally, a simple injection method was used to prepare submicron JDSs, which were imaged with cryogenic transmission electron microscopy (cryo-TEM). As reported previously, different ratios of the same three-component system yielded a variety of structures including homogenous onion-like vesicles, core-shell structures, and completely self-sorted hydrogenated and fluorinated vesicles. Taken together with the JDSs reported herein, a self-sorting pathway is revealed as a function of the relative concentration of the hybrid JD, which may serve to stabilize the interface between hydrogenated and fluorinated bilayers. The fission-like pathway suggests the possibility of fusion and fission processes in biological systems that do not require the assistance of proteins but instead may result from alterations in the ratios of membrane composition.

Membranes, energetics, and evolution across the prokaryote-eukaryote divide

The evolution of the eukaryotic cell marked a profound moment in Earth’s history, with most of the visible biota coming to rely on intracellular membrane-bound organelles. It has been suggested that this evolutionary transition was critically dependent on the movement of ATP synthesis from the cell surface to mitochondrial membranes and the resultant boost to the energetic capacity of eukaryotic cells. However, contrary to this hypothesis, numerous lines of evidence suggest that eukaryotes are no more bioenergetically efficient than prokaryotes. Thus, although the origin of the mitochondrion was a key event in evolutionary history, there is no reason to think membrane bioenergetics played a direct, causal role in the transition from prokaryotes to eukaryotes and the subsequent explosive diversification of cellular and organismal complexity.

Over time, life on Earth has evolved into three large groups: archaea, bacteria, and eukaryotes. The most familiar forms of life – such as fungi, plants and animals – all belong to the eukaryotes. Bacteria and archaea are simpler, single-celled organisms and are collectively referred to as prokaryotes.

The hallmark feature that distinguishes eukaryotes from prokaryotes is that eukaryotic cells contain compartments called organelles that are surrounded by membranes. Each organelle supports different activities in the cell. Mitochondria, for example, are organelles that provide eukaryotes with most of their energy by producing energy-rich molecules called ATP. Prokaryotes lack mitochondria and instead produce their ATP on their cell surface membrane.

Some researchers have suggested that mitochondria might actually be one of the reasons that eukaryotic cells are typically larger than prokaryotes and more varied in their shape and structure. The thinking is that producing ATP on dedicated membranes inside the cell, rather than on the cell surface, boosted the amount of energy available to eukaryotic cells and allowed them to diversify more. However, other researchers are not convinced by this view. Moreover, some recent evidence suggested that eukaryotes are no more efficient in producing energy than prokaryotes.

Lynch and Marinov have now used computational and comparative analysis to compare the energy efficiency of different organisms including prokaryotes and eukaryotes grown under defined conditions. To do the comparison, the results were scaled based on cell volume and the total surface area deployed in energy production.

From their findings, Lynch and Marinov concluded that mitochondria did not enhance how much energy eukaryotes could produce per unit of cell volume in any substantial way. Although the origin of mitochondria was certainly a key event in evolutionary history, it is unlikely to have been responsible for the diversity and complexity of today’s life forms.

Identification of Proteins Associated with Multilamellar Bodies Produced by Dictyostelium discoideum

Dictyostelium discoideum amoebae produce and secrete multilamellar bodies (MLBs) when fed digestible bacteria. The aim of the present study was to elucidate the proteic content of MLBs. The lipid composition of MLBs is mainly amoebal in origin, suggesting that MLB formation is a protozoa-driven process that could play a significant role in amoebal physiology. We identified four major proteins on purified MLBs using mass spectrometry in order to better understand the molecular mechanisms governing MLB formation and, eventually, to elucidate the true function of MLBs. These proteins were SctA, PhoPQ, PonC and a protein containing a cytidine/deoxycytidylate deaminase (CDD) zinc-binding region. SctA is a component of pycnosomes, which are membranous materials that are continuously secreted by amoebae. The presence of SctA on MLBs was confirmed by immunofluorescence and Western blotting using a specific anti-SctA antibody. The CDD protein may be one of the proteins recognized by the H36 antibody, which was used as a MLB marker in a previous study. The function of the CDD protein is unknown. Immunofluorescence and flow cytometric analyses confirmed that the H36 antibody is a better marker of MLBs than the anti-SctA antibody. This study is an additional step to elucidate the potential role of MLBs and revealed that only a small set of proteins appeared to be present on MLBs.

Packaging of Campylobacter jejuni into Multilamellar Bodies by the Ciliate Tetrahymena pyriformis

Campylobacter jejuniis the leading cause of bacterial gastroenteritis worldwide. Transmission to humans occurs through consumption of contaminated food or water. The conditions affecting the persistence of C. jejuniin the environment are poorly understood. Some protozoa package and excrete bacteria into multilamellar bodies (MLBs). Packaged bacteria are protected from deleterious conditions, which increases their survival. We hypothesized that C. jejuni could be packaged under aerobic conditions by the amoeba Acanthamoeba castellanii or the ciliate Tetrahymena pyriformis, both of which are able to package other pathogenic bacteria.A. castellanii did not produce MLBs containing C. jejuni In contrast, when incubated with T. pyriformis,C. jejuni was ingested, packaged in MLBs, and then expelled into the milieu. The viability of the bacteria inside MLBs was confirmed by microscopic analyses. The kinetics of C. jejuni culturability showed that packaging increased the survival of C. jejuniup to 60 h, in contrast to the strong survival defect seen in ciliate-free culture. This study suggests that T. pyriformis may increase the risk of persistence of C. jejuniin the environment and its possible transmission between different reservoirs in food and potable water through packaging.

Amoeba-resisting bacteria found in multilamellar bodies secreted by Dictyostelium discoideum: social amoebae can also package bacteria

Many bacteria can resist phagocytic digestion by various protozoa. Some of these bacteria (all human pathogens) are known to be packaged in multilamellar bodies produced in the phagocytic pathway of the protozoa and that are secreted into the extracellular milieu. Packaged bacteria are protected from harsh conditions, and the packaging process is suspected to promote bacterial persistence in the environment. To date, only a limited number of protozoa, belonging to free-living amoebae and ciliates, have been shown to perform bacteria packaging. It is still unknown if social amoebae can do bacteria packaging. The link between the capacity of 136 bacterial isolates to resist the grazing of the social amoeba Dictyostelium discoideum and to be packaged by this amoeba was investigated in the present study. The 45 bacterial isolates displaying a resisting phenotype were tested for their capacity to be packaged. A total of seven isolates from Cupriavidus, Micrococcus, Microbacterium and Rathayibacter genera seemed to be packaged and secreted by D. discoideum based on immunofluorescence results. Electron microscopy confirmed that the Cupriavidus and Rathayibacter isolates were formally packaged. These results show that social amoebae can package some bacteria from the environment revealing a new aspect of microbial ecology.

The many forms of a pleomorphic bacterial pathogen-the developmental network of Legionella pneumophila

Legionella pneumophila is a natural intracellular bacterial parasite of free-living freshwater protozoa and an accidental human pathogen that causes Legionnaires' disease. L. pneumophila differentiates, and does it in style. Recent experimental data on L. pneumophila's differentiation point at the existence of a complex network that involves many developmental forms. We intend readers to: (i) understand the biological relevance of L. pneumophila's forms found in freshwater and their potential to transmit Legionnaires' disease, and (ii) learn that the common depiction of L. pneumophila's differentiation as a biphasic developmental cycle that alternates between a replicative and a transmissive form is but an oversimplification of the actual process. Our specific objectives are to provide updates on the molecular factors that regulate L. pneumophila's differentiation (Section The Differentiation Process and Its Regulation), and describe the developmental network of L. pneumophila (Section Dissecting Lp's Developmental Network), which for clarity's sake we have dissected into five separate developmental cycles. Finally, since each developmental form seems to contribute differently to the human pathogenic process and the transmission of Legionnaires' disease, readers are presented with a challenge to develop novel methods to detect the various L. pneumophila forms present in water (Section Practical Implications), as a means to improve our assessment of risk and more effectively prevent legionellosis outbreaks.

Defective lysosome maturation and Legionella pneumophila replication in Dictyostelium cells mutant for the Arf GAP ACAP-A

Dictyostelium discoideum ACAP-A is an Arf GTPase-activating protein (GAP) involved in cytokinesis, cell migration and actin cytoskeleton dynamics. In mammalian cells, ACAP family members regulate endocytic protein trafficking. Here, we explored the function of ACAP-A in the endocytic pathway of D. discoideum. In the absence of ACAP-A, the efficiency of fusion between post-lysosomes and the plasma membrane was reduced, resulting in the accumulation of post-lysosomes. Moreover, internalized fluid-phase markers showed extended intracellular transit times, and the transfer kinetics of phagocyted particles from lysosomes to post-lysosomes was reduced. Neutralization of lysosomal pH, one essential step in lysosome maturation, was also delayed. Whereas expression of ACAP-A-GFP in acapA(-) cells restored normal particle transport kinetics, a mutant ACAP-A protein with no GAP activity towards the small GTPase ArfA failed to complement this defect. Taken together, these data support a role for ACAP-A in maturation of lysosomes into post-lysosomes through an ArfA-dependent mechanism. In addition, we reveal that ACAP-A is required for efficient intracellular growth of Legionella pneumophila, a pathogen known to subvert the endocytic host cell machinery for replication. This further emphasizes the role of ACAP-A in the endocytic pathway.

Secondary ion mass spectrometry imaging of Dictyostelium discoideum aggregation streams

High resolution imaging mass spectrometry could become a valuable tool for cell and developmental biology, but both, high spatial and mass spectral resolution are needed to enable this. In this report, we employed Bi₃ bombardment time-of-flight (Bi₃ ToF-SIMS) and C₆₀ bombardment Fourier transform ion cyclotron resonance secondary ion mass spectrometry (C₆₀ FTICR-SIMS) to image Dictyostelium discoideum aggregation streams. Nearly 300 lipid species were identified from the aggregation streams. High resolution mass spectrometry imaging (FTICR-SIMS) enabled the generation of multiple molecular ion maps at the nominal mass level and provided good coverage for fatty acyls, prenol lipids, and sterol lipids. The comparison of Bi₃ ToF-SIMS and C₆₀ FTICR-SIMS suggested that while the first provides fast, high spatial resolution molecular ion images, the chemical complexity of biological samples warrants the use of high resolution analyzers for accurate ion identification.

Potential role of bacteria packaging by protozoa in the persistence and transmission of pathogenic bacteria

Many pathogenic bacteria live in close association with protozoa. These unicellular eukaryotic microorganisms are ubiquitous in various environments. A number of protozoa such as amoebae and ciliates ingest pathogenic bacteria, package them usually in membrane structures, and then release them into the environment. Packaged bacteria are more resistant to various stresses and are more apt to survive than free bacteria. New evidence indicates that protozoa and not bacteria control the packaging process. It is possible that packaging is more common than suspected and may play a major role in the persistence and transmission of pathogenic bacteria. To confirm the role of packaging in the propagation of infections, it is vital that the molecular mechanisms governing the packaging of bacteria by protozoa be identified as well as elements related to the ecology of this process in order to determine whether packaging acts as a Trojan Horse.