Survival In Diverse Environments Research Articles

Population genomic evidence of structured and connected Plasmodium vivax populations under host selection in Latin America.

Pathogen genomic epidemiology has the potential to provide a deep understanding of population dynamics, facilitating strategic planning of interventions, monitoring their impact, and enabling timely responses, and thereby supporting control and elimination efforts of parasitic tropical diseases. Plasmodium vivax, responsible for most malaria cases outside Africa, shows high genetic diversity at the population level, driven by factors like sub-patent infections, a hidden reservoir of hypnozoites, and early transmission to mosquitoes. While Latin America has made significant progress in controlling Plasmodium falciparum, it faces challenges with residual P. vivax. To characterize genetic diversity and population structure and dynamics, we have analyzed the largest collection of P. vivax genomes to date, including 1474 high-quality genomes from 31 countries across Asia, Africa, Oceania, and America. While P. vivax shows high genetic diversity globally, Latin American isolates form a distinctive population, which is further divided into sub-populations and occasional clonal pockets. Genetic diversity within the continent was associated with the intensity of transmission. Population differentiation exists between Central America and the North Coast of South America, vs. the Amazon Basin, with significant gene flow within the Amazon Basin, but limited connectivity between the Northwest Coast and the Amazon Basin. Shared genomic regions in these parasite populations indicate adaptive evolution, particularly in genes related to DNA replication, RNA processing, invasion, and motility - crucial for the parasite's survival in diverse environments. Understanding these population-level adaptations is crucial for effective control efforts, offering insights into potential mechanisms behind drug resistance, immune evasion, and transmission dynamics.

Diversity of gut microbiome in Rocky Mountainsnail across its native range.

The animal gut microbiome is often a key requirement for host nutrition, digestion, and immunity, and can shift in relation to host geography and environmental factors. However, ecological drivers of microbiome community assembly across large geographic ranges have rarely been examined in invertebrates. Oreohelix strigosa (Rocky Mountainsnail) is a widespread land snail found in heterogeneous environments across the mountainous western United States. It is ideally suited for biogeography studies due to its broad distribution, low migration, and low likelihood of passive transport via other animals. This study aims to uncover large-scale geographic shifts in the composition of O. strigosa gut microbiomes by using 16S rRNA gene sequencing on samples from across its native range. Additionally, we elucidate smaller-scale microbiome variation using samples collected only within Colorado. Results show that gut microbiomes vary significantly across broad geographic ranges. Several possible ecological drivers, including soil and vegetation composition, habitat complexity, habitat type, and human impact, collectively explained 27% of the variation across Coloradan O. strigosa gut microbiomes. Snail gut microbiomes show more similarity to vegetation than soil microbiomes. Gut microbial richness was highest in the rocky habitats and increased significantly in the most disturbed habitats (low complexity, high human impact), potentially indicating signs of dysbiosis in the snails' gut microbiomes. These small-scale environmental factors may be driving changes in O. strigosa gut microbiome composition seen across large-scale geography. This knowledge will also help us better understand how microbial associations influence species survival in diverse environments and aid wildlife conservation efforts.

Genetic atlas of hygro-and thermosensory cells in the vinegar fly Drosophila melanogaster

The ability of animals to perceive and respond to sensory information is essential for their survival in diverse environments. While much progress has been made in understanding various sensory modalities, the sense of hygrosensation, which involves the detection and response to humidity, remains poorly understood. In this study, we focused on the hygrosensory, and closely related thermosensory, systems in the vinegar fly Drosophila melanogaster to unravel the molecular profile of the cells of these senses. Using a transcriptomic analysis of over 37,000 nuclei, we identified twelve distinct clusters of cells corresponding to temperature-sensing arista neurons, humidity-sensing sacculus neurons, and support cells relating to these neurons. By examining the expression of known and novel marker genes, we validated the identity of these clusters and characterized their gene expression profiles. We found that each cell type could be characterized by a unique expression profile of ion channels, GPCR signaling molecules, synaptic vesicle cycle proteins, and cell adhesion molecules. Our findings provide valuable insights into the molecular basis of hygro- and thermosensation. Understanding the mechanisms underlying hygro- and thermosensation may shed light on the broader understanding of sensory systems and their adaptation to different environmental conditions in animals.

Transitioning from Soil to Host: Comparative Transcriptome Analysis Reveals the Burkholderia pseudomallei Response to Different Niches.

Burkholderia pseudomallei, a soil and water saprophyte, is responsible for the tropical human disease melioidosis. A hundred years since its discovery, there is still much to learn about B. pseudomallei proteins that are essential for the bacterium's survival in and interaction with the infected host, as well as their roles within the bacterium's natural soil habitat. To address this gap, bacteria grown under conditions mimicking the soil environment were subjected to transcriptome sequencing (RNA-seq) analysis. A dual RNA-seq approach was used on total RNA from spleens isolated from a B. pseudomallei mouse infection model at 5 days postinfection. Under these conditions, a total of 1,434 bacterial genes were induced, with 959 induced in the soil environment and 475 induced in bacteria residing within the host. Genes encoding metabolism and transporter proteins were induced when the bacteria were present in soil, while virulence factors, metabolism, and bacterial defense mechanisms were upregulated during active infection of mice. On the other hand, capsular polysaccharide and quorum-sensing pathways were inhibited during infection. In addition to virulence factors, reactive oxygen species, heat shock proteins, siderophores, and secondary metabolites were also induced to assist bacterial adaptation and survival in the host. Overall, this study provides crucial insights into the transcriptome-level adaptations which facilitate infection by soil-dwelling B. pseudomallei. Targeting novel therapeutics toward B. pseudomallei proteins required for adaptation provides an alternative treatment strategy given its intrinsic antimicrobial resistance and the absence of a vaccine. IMPORTANCE Burkholderia pseudomallei, a soil-dwelling bacterium, is the causative agent of melioidosis, a fatal infectious disease of humans and animals. The bacterium has a large genome consisting of two chromosomes carrying genes that encode proteins with important roles for survival in diverse environments as well as in the infected host. While a general mechanism of pathogenesis has been proposed, it is not clear which proteins have major roles when the bacteria are in the soil and whether the same proteins are key to successful infection and spread. To address this question, we grew the bacteria in soil medium and then in infected mice. At 5 days postinfection, bacteria were recovered from infected mouse organs and their gene expression was compared against that of bacteria grown in soil medium. The analysis revealed a list of genes expressed under soil growth conditions and a different set of genes encoding proteins which may be important for survival, replication, and dissemination in an infected host. These proteins are a potential resource for understanding the full adaptation mechanism of this pathogen. In the absence of a vaccine for melioidosis and with treatment being reliant on combinatorial antibiotic therapy, these proteins may be ideal targets for designing antimicrobials to treat melioidosis.

RIViT-seq enables systematic identification of regulons of transcriptional machineries

Transcriptional regulation is a critical process to ensure expression of genes necessary for growth and survival in diverse environments. Transcription is mediated by multiple transcription factors including activators, repressors and sigma factors. Accurate computational prediction of the regulon of target genes for transcription factors is difficult and experimental identification is laborious and not scalable. Here, we demonstrate regulon identification by in vitro transcription-sequencing (RIViT-seq) that enables systematic identification of regulons of transcription factors by combining an in vitro transcription assay and RNA-sequencing. Using this technology, target genes of 11 sigma factors were identified in Streptomyces coelicolor A3(2). The RIViT-seq data expands the transcriptional regulatory network in this bacterium, discovering regulatory cascades and crosstalk between sigma factors. Implementation of RIViT-seq with other transcription factors and in other organisms will improve our understanding of transcriptional regulatory networks across biology.

Revising the Role of Cortical Cytoskeleton during Secretion: Actin and Myosin XI Function in Vesicle Tethering.

In plants, secretion of cell wall components and membrane proteins plays a fundamental role in growth and development as well as survival in diverse environments. Exocytosis, as the last step of the secretory trafficking pathway, is a highly ordered and precisely controlled process involving tethering, docking, and fusion of vesicles at the plasma membrane (PM) for cargo delivery. Although the exocytic process and machinery are well characterized in yeast and animal models, the molecular players and specific molecular events that underpin late stages of exocytosis in plant cells remain largely unknown. Here, by using the delivery of functional, fluorescent-tagged cellulose synthase (CESA) complexes (CSCs) to the PM as a model system for secretion, as well as single-particle tracking in living cells, we describe a quantitative approach for measuring the frequency of vesicle tethering events. Genetic and pharmacological inhibition of cytoskeletal function, reveal that the initial vesicle tethering step of exocytosis is dependent on actin and myosin XI. In contrast, treatments with the microtubule inhibitor, oryzalin, did not significantly affect vesicle tethering or fusion during CSC exocytosis but caused a minor increase in transient or aborted tethering events. With data from this new quantitative approach and improved spatiotemporal resolution of single particle events during secretion, we generate a revised model for the role of the cortical cytoskeleton in CSC trafficking.

Repeated evolution of circadian clock dysregulation in cavefish populations.

Circadian rhythms are nearly ubiquitous throughout nature, suggesting they are critical for survival in diverse environments. Organisms inhabiting largely arrhythmic environments, such as caves, offer a unique opportunity to study the evolution of circadian rhythms in response to changing ecological pressures. Populations of the Mexican tetra, Astyanax mexicanus, have repeatedly invaded caves from surface rivers, where individuals must contend with perpetual darkness, reduced food availability, and limited fluctuations in daily environmental cues. To investigate the molecular basis for evolved changes in circadian rhythms, we investigated rhythmic transcription across multiple independently-evolved cavefish populations. Our findings reveal that evolution in a cave environment has led to the repeated disruption of the endogenous biological clock, and its entrainment by light. The circadian transcriptome shows widespread reductions and losses of rhythmic transcription and changes to the timing of the activation/repression of core-transcriptional clock. In addition to dysregulation of the core clock, we find that rhythmic transcription of the melatonin regulator aanat2 and melatonin rhythms are disrupted in cavefish under darkness. Mutants of aanat2 and core clock gene rorca disrupt diurnal regulation of sleep in A. mexicanus, phenocopying circadian modulation of sleep and activity phenotypes of cave populations. Together, these findings reveal multiple independent mechanisms for loss of circadian rhythms in cavefish populations and provide a platform for studying how evolved changes in the biological clock can contribute to variation in sleep and circadian behavior.

Development of a Novel Short Synthetic Antibacterial Peptide Derived from the Swallowtail Butterfly Papilio xuthus Larvae.

Insects possess biological defense systems that can effectively combat the invasion of external microorganisms and viruses, thereby supporting their survival in diverse environments. Antimicrobial peptides (AMPs) represent a fast-acting weapon against invading pathogens, including various bacterial or fungal strains. A 37-residue antimicrobial peptide, papiliocin, derived from the swallowtail butterfly Papilio xuthus larvae, showed significant antimicrobial activities against several human pathogenic bacterial and fungal strains. Jelleines, isolated as novel antibacterial peptides from the Royal Jelly (RJ) of bees, exhibit broad-spectrum protection against microbial infections. In this study, we developed a novel antimicrobial peptide, PAJE (RWKIFKKPFKISIHL-NH2), which is a hybrid peptide prepared by combining 1-7 amino acid residues (RWKIFKK-NH2) of papiliocin and 1-8 amino acid residues (PFKISIHL-NH2) of Jelleine-1 to alter length, charge distribution, net charge, volume, amphipaticity, and improve bacterial membrane interactions. This novel peptide exhibited increased hydrophobicity and net positive charge for binding effectively to the negatively charged membrane. PAJE demonstrated antimicrobial activity against both gram-negative and gram-positive bacteria, with very low toxicity to eukaryotic cells and an inexpensive process of synthesis. Collectively, these findings suggest that this novel peptide possesses great potential as an antimicrobial agent.

RETRACTED ARTICLE: The role of seed appendage in improving the adaptation of a species in definite seasons: a case study of Atriplex centralasiatica

BackgroundAs a common accompanying dispersal structure, specialized seed appendages play a critical role in the successful germination and dispersal of many plants, and are regarded as an adaptation character for plants survival in diverse environments. However, little is known about how the appendages modulate the linkage between germination and environmental factors. Here, we tested the responses of germination to seasonal environmental signals (temperature and humidity) via seed appendages using Atriplex centralasiatica, which is widely distributed in salt marshlands with dry-cold winter in northern China. Three types of heteromorphic diaspores that differ in morphology of persistent bracteole and dormancy levels are produced in an individual plant of A. centralasiatica.ResultsExcept for the nondormant diaspore (type A, with a brown seed enclosed in a persistent bracteole), bracteoles regulated inner seed dormancy of the other two dormant diaspore types, i.e., type B (flat diaspore with a black inner seed) and type C (globular diaspore with a black inner seed). For types B and C, germination of bracteole-free seeds was higher than that of intact diaspores, and was limited severely when incubated in the bracteole-soaking solution. Dormancy was released at a low temperature (< 10 °C) and suitable humidity (5–15%) condition. Oppositely, high temperature and unfit humidity induced secondary dormancy via inhibitors released by bracteoles. Type C with deeper dormancy needed more stringent conditions for dormancy release and was easier for dormancy inducement than type B. The germination windows were broadened and the time needed for dormancy release decreased after the bracteole flushing for the two dormant types in the field condition.ConclusionsBracteoles determine the germination adaptation by bridging seeds and environmental signals and promising seedlings establishment only in proper seasons, which may also restrict species geographical distribution and shift species distributing ranges under the global climate change scenarios.

Genome-Wide Transposon Screen of a Pseudomonas syringae mexB Mutant Reveals the Substrates of Efflux Transporters.

Bacteria express numerous efflux transporters that confer resistance to diverse toxicants present in their environment. Due to a high level of functional redundancy of these transporters, it is difficult to identify those that are of most importance in conferring resistance to specific compounds. The resistance-nodulation-division (RND) protein family is one such example of redundant transporters that are widespread among Gram-negative bacteria. Within this family, the MexAB-OprM protein complex is highly expressed and conserved among Pseudomonas species. We exposed barcoded transposon mutant libraries in isogenic wild-type and ΔmexB backgrounds in P. syringae B728a to diverse toxic compounds in vitro to identify mutants with increased susceptibility to these compounds. Mutants with mutations in genes encoding both known and novel redundant transporters but with partially overlapping substrate specificities were observed in a ΔmexB background. Psyr_0228, an uncharacterized member of the major facilitator superfamily of transporters, preferentially contributes to tolerance of acridine orange and acriflavine. Another transporter located in the inner membrane, Psyr_0541, contributes to tolerance of acriflavine and berberine. The presence of multiple redundant, genomically encoded efflux transporters appears to enable bacterial strains to tolerate a diversity of environmental toxins. This genome-wide screen performed in a hypersusceptible mutant strain revealed numerous transporters that would otherwise be dispensable under these conditions. Bacterial strains such as P. syringae that likely encounter diverse toxins in their environment, such as in association with many different plant species, probably benefit from possessing multiple redundant transporters that enable versatility with respect to toleration of novel toxicants.IMPORTANCE Bacteria use protein pumps to remove toxic compounds from the cell interior, enabling survival in diverse environments. These protein pumps can be highly redundant, making their targeted examination difficult. In this study, we exposed mutant populations of Pseudomonas syringae to diverse toxicants to identify pumps that contributed to survival in those conditions. In parallel, we examined pump redundancy by testing mutants of a population lacking the primary efflux transporter responsible for toxin tolerance. We identified partial substrate overlap for redundant transporters, as well as several pumps that appeared more substrate specific. For bacteria that are found in diverse environments, having multiple, partially redundant efflux pumps likely allows flexibility in habitat colonization.

QTL Determining Diel Flight Activity in Male Culex pipiens Mosquitoes.

Members of the Culex pipiens complex differ in physiological traits that facilitate their survival in diverse environments. Assortative mating within the complex occurs in some regions where autogenous (the ability to lay a batch of eggs without a blood meal) and anautogenous populations are sympatric, and differences in mating behaviors may be involved. For example, anautogenous populations mate in flight/swarms, while autogenous populations often mate at rest. Here, we characterized flight activity of males and found that anautogenous strain males were crepuscular, while autogenous strain males were crepuscular and nocturnal, with earlier activity onset times. We conducted quantitative trait locus (QTL) mapping to explore the genetic basis of circadian chronotype (crepuscular vs. crepuscular and nocturnal) and time of activity onset. One major-effect QTL was identified for chronotype, while 3 QTLs were identified for activity onset. The highest logarithm of the odds (LOD) score for the chronotype QTL coincides with a chromosome 3 marker that contains a 15-nucleotide indel within the coding region of the canonical clock gene, cryptochrome 2. Sequencing of this locus in 7 different strains showed that the C-terminus of CRY2 in the autogenous forms contain deletions not found in the anautogenous forms. Consequently, we monitored activity in constant darkness and found males from the anautogenous strain exhibited free running periods of ~24 h while those from the autogenous strain were ~22 h. This study provides novel insights into the genetic basis of flight behaviors that likely reflect adaptation to their distinct ecological niches.

Azetidine-Containing Alkaloids Produced by a Quorum-Sensing Regulated Nonribosomal Peptide Synthetase Pathway in Pseudomonas aeruginosa.

Pseudomonas aeruginosa displays an impressive metabolic versatility, which ensures its survival in diverse environments. Reported herein is the identification of rare azetidine-containing alkaloids from P. aeruginosa PAO1, termed azetidomonamides, which are derived from a conserved, quorum-sensing regulated nonribosomal peptide synthetase (NRPS) pathway. Biosynthesis of the azetidine motif has been elucidated by gene inactivation, feeding experiments, and biochemical characterization in vitro, which involves a new S-adenosylmethionine-dependent enzyme to produce azetidine 2-carboxylic acid as an unusual building block of NRPS. The mutants of P. aeruginosa unable to produce azetidomonamides had an advantage in growth at high cell density in vitro and displayed rapid virulence in Galleria mellonella model, inferring functional roles of azetidomonamides in the host adaptation. This work opens the avenue to study the biological functions of azetidomonamides and related compounds in pathogenic and environmental bacteria.

Azetidine‐Containing Alkaloids Produced by a Quorum‐Sensing Regulated Nonribosomal Peptide Synthetase Pathway in Pseudomonas aeruginosa

AbstractPseudomonas aeruginosa displays an impressive metabolic versatility, which ensures its survival in diverse environments. Reported herein is the identification of rare azetidine‐containing alkaloids from P. aeruginosa PAO1, termed azetidomonamides, which are derived from a conserved, quorum‐sensing regulated nonribosomal peptide synthetase (NRPS) pathway. Biosynthesis of the azetidine motif has been elucidated by gene inactivation, feeding experiments, and biochemical characterization in vitro, which involves a new S‐adenosylmethionine‐dependent enzyme to produce azetidine 2‐carboxylic acid as an unusual building block of NRPS. The mutants of P. aeruginosa unable to produce azetidomonamides had an advantage in growth at high cell density in vitro and displayed rapid virulence in Galleria mellonella model, inferring functional roles of azetidomonamides in the host adaptation. This work opens the avenue to study the biological functions of azetidomonamides and related compounds in pathogenic and environmental bacteria.

T6SS intraspecific competition orchestrates Vibrio cholerae genotypic diversity.

Vibrio cholerae is a diverse species that inhabits a wide range of environments from copepods in brackish water to the intestines of humans. In order to remain competitive, V. cholerae uses the versatile type-VI secretion system (T6SS) to secrete anti-prokaryotic and anti-eukaryotic effectors. In addition to competing with other bacterial species, V. cholerae strains also compete with one another. Some strains are able to coexist, and are referred to as belonging to the same compatibility group. Challenged by diverse competitors in various environments, different V. choleare strains secrete different combination of effectors - presumably to best suit their niche. Interestingly, all pandemic V. cholerae strains encode the same three effectors. In addition to the diversity displayed in the encoded effectors, the regulation of V. cholerae also differs between strains. Two main layers of regulation appear to exist. One strategy connects T6SS activity with behavior that is suited to fighting eukaryotic cells, while the other is linked with natural competence - the ability of the bacterium to acquire and incorporate extracellular DNA. This relationship between bacterial killing and natural competence is potentially a source of diversification for V. cholerae as it has been shown to incorporate the DNA of cells recently killed through T6SS activity. It is through this process that we hypothesize the transfer of virulence factors, including T6SS effector modules, to happen. Switching of T6SS effectors has the potential to change the range of competitors V. cholerae can kill and to newly define which strains V. cholerae can co-exist with, two important parameters for survival in diverse environments.

Thermoregulation of Biofilm Formation in Burkholderia pseudomallei Is Disrupted by Mutation of a Putative Diguanylate Cyclase.

Burkholderia pseudomallei, a tier 1 select agent and the etiological agent of melioidosis, transitions from soil and aquatic environments to infect a variety of vertebrate and invertebrate hosts. During the transition from an environmental saprophyte to a mammalian pathogen, B. pseudomallei encounters and responds to rapidly changing environmental conditions. Environmental sensing systems that control cellular levels of cyclic di-GMP promote pathogen survival in diverse environments. Cyclic di-GMP controls biofilm production, virulence factors, and motility in many bacteria. This study is an evaluation of cyclic di-GMP-associated genes that are predicted to metabolize and interact with cyclic di-GMP as identified from the annotated genome of B. pseudomallei 1026b. Mutants containing transposon disruptions in each of these genes were characterized for biofilm formation and motility at two temperatures that reflect conditions that the bacteria encounter in the environment and during the infection of a mammalian host. Mutants with transposon insertions in a known phosphodiesterase (cdpA) and a predicted hydrolase (Bp1026b_I2285) gene exhibited decreased motility regardless of temperature. In contrast, the phenotypes exhibited by mutants with transposon insertion mutations in a predicted diguanylate cyclase gene (Bp1026b_II2523) were strikingly influenced by temperature and were dependent on a conserved GG(D/E)EF motif. The transposon insertion mutant exhibited enhanced biofilm formation at 37°C but impaired biofilm formation at 30°C. These studies illustrate the importance of studying behaviors regulated by cyclic di-GMP under varied environmental conditions in order to better understand cyclic di-GMP signaling in bacterial pathogens.IMPORTANCE This report evaluates predicted cyclic di-GMP binding and metabolic proteins from Burkholderia pseudomallei 1026b, a tier 1 select agent and the etiologic agent of melioidosis. Transposon insertion mutants with disruptions in each of the genes encoding these predicted proteins were characterized in order to identify key components of the B. pseudomallei cyclic di-GMP-signaling network. A predicted hydrolase and a phosphodiesterase that modulate swimming motility were identified, in addition to a diguanylate cyclase that modulates biofilm formation and motility in response to temperature. These studies warrant further evaluation of the contribution of cyclic di-GMP to melioidosis in the context of pathogen acquisition from environmental reservoirs and subsequent colonization, dissemination, and persistence within the host.

Staying in Shape: the Impact of Cell Shape on Bacterial Survival in Diverse Environments.

Bacteria display an abundance of cellular forms and can change shape during their life cycle. Many plausible models regarding the functional significance of cell morphology have emerged. A greater understanding of the genetic programs underpinning morphological variation in diverse bacterial groups, combined with assays of bacteria under conditions that mimic their varied natural environments, from flowing freshwater streams to diverse human body sites, provides new opportunities to probe the functional significance of cell shape. Here we explore shape diversity among bacteria, at the levels of cell geometry, size, and surface appendages (both placement and number), as it relates to survival in diverse environments. Cell shape in most bacteria is determined by the cell wall. A major challenge in this field has been deconvoluting the effects of differences in the chemical properties of the cell wall and the resulting cell shape perturbations on observed fitness changes. Still, such studies have begun to reveal the selective pressures that drive the diverse forms (or cell wall compositions) observed in mammalian pathogens and bacteria more generally, including efficient adherence to biotic and abiotic surfaces, survival under low-nutrient or stressful conditions, evasion of mammalian complement deposition, efficient dispersal through mucous barriers and tissues, and efficient nutrient acquisition.

Distinct chitinases are expressed during various growth phases of the human pathogen Paracoccidioides brasiliensis

The aim of this work was the partial purification and subsequent evaluation of chitinase expression during the various growth phases of Paracoccidioides brasiliensis. Initially, PbCTS1r was expressed as a recombinant protein and displayed enzymatic activity against 4-MU-[N-acetylglucosamine (GlcNAc)]3 and 4-MU-(GlcNAc)2. Two proteins, 45 kDa and 39 kDa in size, were partially purified from P. brasiliensis yeast crude extract using cation-exchange chromatography coupled with HPLC and were characterised as PbCTS1 and PbCTS2, respectively. Anti-PbCTS1r antibody recognised two proteins in the crude extracts of yeast and the transitional stage between mycelial and yeast phases. In crude extracts of mycelium, only the 45 kDa protein was detected. However, quantitative real-time polymerase chain reaction led to the detection of small quantities of Pbcts2 transcript in the mycelial phase. In the yeast cell wall extract, only the 39 kDa protein was detected. Moreover, both proteins were secreted by the yeast parasitic phase, suggesting that these proteins participate in the modulation of the fungal environment. Phylogenetic analysis of the predicted PbCTS1 and PbCTS2 proteins indicated that they code for distinct chitinases in P. brasiliensis. During evolution, P. brasiliensis could have acquired the paralogues Pbcts1 and Pbcts2 for growth and survival in diverse environments in both saprophytic and parasitic phases.

Actin Polymerization Drives Septation of Listeria monocytogenes namA Hydrolase Mutants, Demonstrating Host Correction of a Bacterial Defect

The Gram-positive bacterial cell wall presents a structural barrier that requires modification for protein secretion and large-molecule transport as well as for bacterial growth and cell division. The Gram-positive bacterium Listeria monocytogenes adjusts cell wall architecture to promote its survival in diverse environments that include soil and the cytosol of mammalian cells. Here we provide evidence for the enzymatic flexibility of the murein hydrolase NamA and demonstrate that bacterial septation defects associated with a loss of NamA are functionally complemented by physical forces associated with actin polymerization within the host cell cytosol. L. monocytogenes ΔnamA mutants formed long bacterial chains during exponential growth in broth culture; however, normal septation could be restored if mutant cells were cocultured with wild-type L. monocytogenes bacteria or by the addition of exogenous NamA. Surprisingly, ΔnamA mutants were not significantly attenuated for virulence in mice despite the pronounced exponential growth septation defect. The physical force of L. monocytogenes-mediated actin polymerization within the cytosol was sufficient to sever ΔnamA mutant intracellular chains and thereby enable the process of bacterial cell-to-cell spread so critical for L. monocytogenes virulence. The inhibition of actin polymerization by cytochalasin D resulted in extended intracellular bacterial chains for which septation was restored following drug removal. Thus, despite the requirement for NamA for the normal septation of exponentially growing L. monocytogenes cells, the hydrolase is essentially dispensable once L. monocytogenes gains access to the host cell cytosol. This phenomenon represents a notable example of eukaryotic host cell complementation of a bacterial defect.

The contribution of mobile genetic elements to the evolution and ecology of Vibrios

An increase in the frequency of seafood-borne gastroenteritis in humans and Vibrio-related disease of fish and invertebrates has generated interest in the ecology of disease-causing Vibrios and the mechanisms driving their evolution. Genome sequencing studies have indicated a substantial contribution of horizontal gene transfer (HGT) to the evolution of Vibrios. Of particular interest is the contribution of HGT to the evolution of Vibrios pathogens and the adaptation of disease-causing Vibrios for survival in diverse environments. In this review, we discuss the diversity and distribution of mobile genetic elements (MGEs) isolated from Vibrios and the contribution of these elements to the expansion of the ecological and pathogenic niches of the host strain. Much of the research on Vibrio MGEs has focused on understanding phages and plasmids and we will primarily discuss the evolution of these elements and also briefly highlight the other diverse elements characterized from Vibrios, which includes genomic islands and conjugative elements.

INHIBITORY EFFECT OF CLOVE OIL (SYZIUM AROMATICUM) AGAINST LISTERIA MONOCYTOGENES CELLS INCUBATED IN FRESH‐CUT SALMON

ABSTRACT The ability of Listeria monocytogenes to survive and grow at refrigeration temperature in a wide spectrum of foods is a public health concern. Essential oil of clove (Syzium aromaticum) was investigated for its ability to inhibit the growth of this pathogen in food. Three strains of L. monocytogenes (106 cfu/g) were inoculated on fresh‐cut salmon and stored (4C and 25C) for 2 weeks. The effect of clove oil (1% and 2%) on the growth of cells was determined. The results proved that all strains survived and grew at 4C and 25C. In addition, we noted that the growth was inhibited under storage conditions in the presence of clove oil (1% or 2%). Listeria counts in treated samples were 1–4 log10 cfu/g less compared with controls at different intervals during storage. The results revealed the potential of clove oil as a natural preservative in fresh salmon.PRACTICAL APPLICATIONS Listeria monocytogenes continues to be a significant threat to the safety of the food supply. It was isolated from a variety of foods and ready‐to‐eat products and generated a serious public health problem. Because of its growth capacity at refrigerating temperatures and its survival in diverse environments, the control of L. monocytogenes is becoming a challenge.Several agents were used to suppressing contamination by L. monocytogenes, such as the addition of biopreservatives and essential oil. Spices and herbs are commonly used in food preservation because they do not have a strong effect on food quality unlike chemical and synthetic compounds. Clove oil, contains eugenol which when tested on various agar media, has antimicrobial properties, and it was able to restrict the proliferation of L. monocytogenes in food products. For this reason, clove oil has good potential as an antilisterial substance in food preservation as it may be more acceptable to consumers.