Parasite microtubule arrays.

Microtubules are a key component of eukaryotic cell architecture. Regulation of the dynamic growth and shrinkage of microtubules gives cells their shape, allows cells to swim, and drives the separation of chromosomes. Parasites have developed intriguingly divergent biology, seemingly expanding upon and reinventing microtubule use in fascinating ways. These organisms affect life on the planet at scales that are often overlooked: there are likely more parasitic than free-living organisms on Earth, and they have a sizeable influence across ecosystems. As parasites can cause devastating diseases, this in turn drives evolutionary adaptations and species diversity. Parasites are varied, living in all environments and at all scales - from the tiny 2 µm single-celled Plasmodium merozoite that invades red blood cells to the 40 m long Tetragonoporus, a large intestinal tapeworm of whales. To survive in their various niches, parasites have undergone striking adaptations and developed complex life cycles, often involving two or more host species. This diversity is reflected at the cellular level, where unique molecular mechanisms, cytoskeletal structures and organellar compositions are found. Hence, the study of parasite cell biology provides a biological playground for understanding diversity and species diversification. It also facilitates the identification of specific targets to develop urgently needed therapeutics: for example, drugs targeting microtubules are used at large scale to treat intestinal worms and parasites that form tissue cysts in our livers and brains. Here, we discuss some of the curious microtubule arrays found in a small, select number of human-infecting, single-celled parasites of medical importance (Table 1). Our aim is to put a spotlight on distinctive molecular features in a field that promises exciting cell-biological discoveries with the potential for therapeutic breakthroughs.

Optical control of ultrafast structural dynamics in a fluorescent protein.

The photoisomerization reaction of a fluorescent protein chromophore occurs on the ultrafast timescale. The structural dynamics that result from femtosecond optical excitation have contributions from vibrational and electronic processes and from reaction dynamics that involve the crossing through a conical intersection. The creation and progression of the ultrafast structural dynamics strongly depends on optical and molecular parameters. When using X-ray crystallography as a probe of ultrafast dynamics, the origin of the observed nuclear motions is not known. Now, high-resolution pump-probe X-ray crystallography reveals complex sub-ångström, ultrafast motions and hydrogen-bonding rearrangements in the active site of a fluorescent protein. However, we demonstrate that the measured motions are not part of the photoisomerization reaction but instead arise from impulsively driven coherent vibrational processes in the electronic ground state. A coherent-control experiment using a two-colour and two-pulse optical excitation strongly amplifies the X-ray crystallographic difference density, while it fully depletes the photoisomerization process. A coherent control mechanism was tested and confirmed the wave packets assignment.

Nutrinews (covid-19): ação extensionista sobre nutrição, saúde e segurança dos alimentos no contexto da pandemia por sars-cov-2 / Nutrinews (COVID-19): Extensionist action on nutrition, health,and food safety in the context of the SARS-CoV-2 pandemic / Nutrinews (COVID-19): acción extensionista en materia de nutrición, salud y seguridad alimentaria en el contexto de la pandemia del SARS-CoV-2

Introdução:O período pandêmico trouxe inúmeros desafios à saúde da população, entre eles, a manutenção da saúde alimentar, ameaçada pela disseminação de notícias falsas e o desconhecimento da população acerca de sua importância. Nesse contexto, o uso das mídias sociais torna-se um trajeto de aproximação entre educação e saúde.Objetivo:Relatar a experiência obtida através da execução de um projeto de extensão universitáriarelacionado a promoçãoda saúde nutricional via mídias sociais no contexto pandêmico.Metodologia:Trata-se de um estudo descritivo, do tipo relato de experiência, no qual descreve-se a execução do Projeto de extensão universitária: "Descomplicando a nutrição e segurança dos alimentos no contexto da pandemia por SARS-CoV-2".Oprojeto foi desenvolvido através do compartilhamento de publicações e serviços on-lineacerca da segurança de alimentose nutriçãono contexto da pandemia.Utilizou-seuma conta publica no Instagram®e uma comunidade virtual do Whatsapp®como veículos de informação e promoção de saúdepara população. Resultados:Entre o período de junho a dezembro de 2021, a conta do Instagram®atingiu um total de 359 seguidores,e realizou centenas de postagens, dentre posts, vídeose stories,alcançando mais de mil contas. Além das publicações, foi oferecido suporte direto, via WhatsApp®,paramanipuladores de alimentos formais e informais acompanhados pelo grupo de extensão.Conclusões:Os conteúdos trabalhadosnas redes sociais tiveram bom alcance,contribuindopara a promoção de saúde e o combate defalsas informaçõesnas redes sociais. Ao passo que, aodesenvolver as atividades, os participantes do projeto socializaramsaberese desenvolveram competências como: tomada de decisões, protagonismo, reflexão, comprometimento, trabalho em equipe e criatividade (AU).

Introduction:The pandemic period has brought numerous challenges to the health of the population, among them, the maintenance of food health, threatened by the spread of false news and the population's lack of knowledge about its importance. In this context, the use ofsocial media becomes a path of approximation between education and health. Objective:To report the experience obtained through the execution of a university extension project related to the promotion of nutritional health via social media in the pandemiccontext.Methodology: This is a descriptive study, of the experience report type, in which the execution of the University Extension Project is described: "Uncomplicating nutrition and food safety in the context of the SARS-CoV-2 pandemic". The project was developed through the sharing of publications and online services about food safety and nutrition in the context of the pandemic. For that, a public Instagram® account and a Whatsapp® virtual community were used as vehicles for information and health promotion for the population. Results:From June to December 2021, the Instagram® account reached a total of 359 followers, and made hundreds of posts, including posts, videos and stories, reaching more than a thousand accounts. In addition to the publications, direct support was offered via WhatsApp® to formal and informal food handlers registered and monitored by the extension group. Conclusions:The content worked on social networks had a good reach, contributing to health promotion and the fight against false information on social networks. While, when developing the activities, the students and the project coordinator shared knowledge and developed skills such as: decision-making, protagonism, reflection, commitment, teamwork and creativity (AU).

Introducción:El período de pandemia ha traído numerosos desafíos para la salud de la población, entre ellos el mantenimiento de una alimentación saludable, amenazada por la difusión de noticias falsas y el desconocimiento de la población sobre su importancia. En este contexto, el uso de las redes sociales se convierte en un camino de aproximación entre la educación y la salud. Objetivo:relatar la experiencia obtenida a través de la ejecución de un proyecto de extensión universitaria relacionado con la promoción de la salud nutricional a través de las redes sociales en el contexto de la pandemia. Metodología: Se trata de un estudio descriptivo, del tipo informede experiencia, en el que se describe la ejecución del Proyecto de Extensión Universitaria: "Descomplicando la nutrición y la seguridad alimentaria en el contexto de la pandemia por SARS-CoV-2". El proyecto se desarrolló a través del intercambio de publicaciones y servicios en línea sobre seguridad alimentaria y nutrición en el contexto de la pandemia. Se utilizó una cuenta pública de Instagram® y una comunidad virtual de Whatsapp® como vehículos de información y promoción de la salud de la población. Resultados:de junio a diciembre de 2021, la cuenta de Instagram® alcanzó un total de 359 seguidores y realizó cientos de publicaciones, entre publicaciones, videos e historias, llegando a más de mil cuentas. Además de publicaciones, se ofreció apoyo directo vía WhatsApp® a manipuladores de alimentos formales e informales monitoreados por el grupo de extensión. Conclusiones:El contenido trabajado en las redes sociales tuvo un buen alcance, contribuyendo a la promoción de la salud y la lucha contra la información falsa en las redes sociales. Mientras que, mediante el desarrollo de las actividades, los participantes del proyecto compartieron conocimientos y desarrollaron habilidades como: toma de decisiones, protagonismo, reflexión, compromiso, trabajo en equipo y creatividad (AU).

Riparin-B as a Potential Inhibitor of AdeABC Efflux System from Acinetobacter baumannii.

Acinetobacter baumannii is an important opportunistic pathogen that causes serious health-related infections, especially in intensive care units. The present study aimed to investigate the antimicrobial activity of Riparin-B (Rip-B) alone and in association with norfloxacin against multidrug-resistant clinical isolates of A. baumannii. For this, the minimum inhibitory concentrations were determined by the microdilution method. For the evaluation of resistance-modulating activity, MIC values for antibiotics were determined in the presence or absence of subinhibitory concentrations of Rip-B or chlorpromazine (CPZ). The AdeABC-AdeRS efflux system genes from these isolates were detected by PCR. Docking studies were also carried out to evaluate the interaction of Riparin-B and the AdeABC-AdeRS efflux system. The study was conducted from 2017 to 2019. The results showed that Rip-B showed weak intrinsic activity against the strains tested. On the other hand, Rip-B was able to modulate norfloxacin's response against A. baumannii strains that express efflux pump-mediated resistance. Docking studies provided projections of the interaction between Rip-B and EtBr with the AdeB protein, suggesting that Rip-B acts by competitive inhibition with the drug. Results found by in vitro and in silico assays suggest that Rip-B, in combination with norfloxacin, has the potential to treat infections caused by multidrug-resistant A. baumanni with efflux pump resistance.

Inhibition of NorA efflux pump of Staphylococcus aureus by anacardic acids isolated from the cashew nutshell liquid of Anacardium occidentale L.

The rising of diseases caused by multidrug-resistant bacteria has encouraged researchers to explore more antimicrobial substances, as well as chemicals capable of potentiating the action of existing ones against multidrug-resistant bacteria. Anacardium occidentale produces a fruit known as cashew nut, filled with a dark, almost black, caustic, and flammable liquid called cashew nutshell liquid (CNSL). The goal of the study was to evaluate the intrinsic antimicrobial activity of the major compounds present in CNSL, called anacardic acids (AA), as well as their possible modulatory action as an adjuvant of Norfloxacin against a Staphylococcus aureus strain overproducing the NorA efflux pump (SA1199B). Microdilution assays were performed to determine the minimum inhibitory concentration (MIC) of AA against different microbial species. Norfloxacin and Ethidium Bromide (EtBr) resistance modulation assays were performed in the presence or absence of AA against SA1199-B. AA showed antimicrobial activity against Gram-positive bacterial strains tested but no activity against Gram-negative bacteria or yeast strains. At subinhibitory concentration, AA reduced the MIC values for Norfloxacin and EtBr against the SA1199-B strain. Furthermore, AA increased the intracellular accumulation of EtBr in this NorA overproducer strain, indicating that AA are NorA inhibitors. Docking analysis showed that AA probably modulates Norfloxacin efflux by spatial impediment at the same binding site of NorA.

Variable microtubule architecture in the malaria parasite.

Microtubules are a ubiquitous eukaryotic cytoskeletal element typically consisting of 13 protofilaments arranged in a hollow cylinder. This arrangement is considered the canonical form and is adopted by most organisms, with rare exceptions. Here, we use in situ electron cryo-tomography and subvolume averaging to analyse the changing microtubule cytoskeleton of Plasmodium falciparum, the causative agent of malaria, throughout its life cycle. Unexpectedly, different parasite forms have distinct microtubule structures coordinated by unique organising centres. In merozoites, the most widely studied form, we observe canonical microtubules. In migrating mosquito forms, the 13 protofilament structure is further reinforced by interrupted luminal helices. Surprisingly, gametocytes contain a wide distribution of microtubule structures ranging from 13 to 18 protofilaments, doublets and triplets. Such a diversity of microtubule structures has not been observed in any other organism to date and is likely evidence of a distinct role in each life cycle form. This data provides a unique view into an unusual microtubule cytoskeleton of a relevant human pathogen.

The malaria parasite chaperonin containing TCP-1 (CCT) complex: Data integration with other CCT proteomes.

The multi-subunit chaperonin containing TCP-1 (CCT) is an essential molecular chaperone that functions in the folding of key cellular proteins. This paper reviews the interactome of the eukaryotic chaperonin CCT and its primary clients, the ubiquitous cytoskeletal proteins, actin and tubulin. CCT interacts with other nascent proteins, especially the WD40 propeller proteins, and also assists in the assembly of several protein complexes. A new proteomic dataset is presented for CCT purified from the human malarial parasite, P. falciparum (PfCCT). The CCT8 subunit gene was C-terminally FLAG-tagged using Selection Linked Integration (SLI) and CCT complexes were extracted from infected human erythrocyte cultures synchronized for maximum expression levels of CCT at the trophozoite stage of the parasite's asexual life cycle. We analyze the new PfCCT proteome and incorporate it into our existing model of the CCT system, supported by accumulated data from biochemical and cell biological experiments in many eukaryotic species. Together with measurements of CCT mRNA, CCT protein subunit copy number and the post-translational and chemical modifications of the CCT subunits themselves, a cumulative picture is emerging of an essential molecular chaperone system sitting at the heart of eukaryotic cell growth control and cell cycle regulation.

Characterization of Apicomplexan Amino Acid Transporters (ApiATs) in the Malaria Parasite Plasmodium falciparum.

During the symptomatic human blood phase, malaria parasites replicate within red blood cells. Parasite proliferation relies on the uptake of nutrients, such as amino acids, from the host cell and blood plasma, requiring transport across multiple membranes. Amino acids are delivered to the parasite through the parasite-surrounding vacuolar compartment by specialized nutrient-permeable channels of the erythrocyte membrane and the parasitophorous vacuole membrane (PVM). However, further transport of amino acids across the parasite plasma membrane (PPM) is currently not well characterized. In this study, we focused on a family of Apicomplexan amino acid transporters (ApiATs) that comprises five members in Plasmodium falciparum. First, we localized four of the P. falciparum ApiATs (PfApiATs) at the PPM using endogenous green fluorescent protein (GFP) tagging. Next, we applied reverse genetic approaches to probe into their essentiality during asexual replication and gametocytogenesis. Upon inducible knockdown and targeted gene disruption, a reduced asexual parasite proliferation was detected for PfApiAT2 and PfApiAT4. Functional inactivation of individual PfApiATs targeted in this study had no effect on gametocyte development. Our data suggest that individual PfApiATs are partially redundant during asexual in vitro proliferation and fully redundant during gametocytogenesis of P. falciparum parasites. IMPORTANCE Malaria parasites live and multiply inside cells. To facilitate their extremely fast intracellular proliferation, they hijack and transform their host cells. This also requires the active uptake of nutrients, such as amino acids, from the host cell and the surrounding environment through various membranes that are the consequence of the parasite's intracellular lifestyle. In this paper, we focus on a family of putative amino acid transporters termed ApiAT. We show expression and localization of four transporters in the parasite plasma membrane of Plasmodium falciparum-infected erythrocytes that represent one interface of the pathogen to its host cell. We probed into the impact of functional inactivation of individual transporters on parasite growth in asexual and sexual blood stages of P. falciparum and reveal that only two of them show a modest but significant reduction in parasite proliferation but no impact on gametocytogenesis, pointing toward dispensability within this transporter family.

Corrigendum: The "Jack-of-all-Trades" Flagellum From Salmonella and E. coli Was Horizontally Acquired From an Ancestral ß-Proteobacterium.

[This corrects the article DOI: 10.3389/fmicb.2021.643180.].

Lpp positions peptidoglycan at the AcrA-TolC interface in the AcrAB-TolC multidrug efflux pump.

The multidrug efflux pumps of Gram-negative bacteria are a class of complexes that span the periplasm, coupling both the inner and outer membranes to expel toxic molecules. The best-characterized example of these tripartite pumps is the AcrAB-TolC complex of Escherichia coli. However, how the complex interacts with the peptidoglycan (PG) cell wall, which is anchored to the outer membrane (OM) by Braun's lipoprotein (Lpp), is still largely unknown. In this work, we present molecular dynamics simulations of a complete, atomistic model of the AcrAB-TolC complex with the inner membrane, OM, and PG layers all present. We find that the PG localizes to the junction of AcrA and TolC, in agreement with recent cryo-tomography data. Free-energy calculations reveal that the positioning of PG is determined by the length and conformation of multiple Lpp copies anchoring it to the OM. The distance between the PG and OM measured in cryo-electron microscopy images of wild-type E. coli also agrees with the simulation-derived spacing. Sequence analysis of AcrA suggests a conserved role for interactions with PG in the assembly and stabilization of efflux pumps, one that may extend to other trans-envelope complexes as well.

Mechanism of the lethal effect of Riparin E against bacterial and yeast strains.

Riparins are alkamides naturally found in the fruits of Aniba riparia (Nees) Mez, but currently synthetic molecules as Riparin E (Rip-E) can be obtained. Potential biological of Rip-E as schistosomicidal agent against Schistosoma mansoni worms, as well as against Staphylococcus aureus strains has already been described. However, the mechanism of action related to antimicrobial activity of Rip-E against bacterial or fungi species has not yet been reported. This study had as objective to evaluate the Rip-E antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as against yeast species of clinical importance. Minimal inhibitory concentrations of the compound against bacterial and yeast strains were determined by microdilution method. To verify if a possible lethal effect caused by Rip-E were related to plasma membrane damage, microbial cells treated with Rip-E were stained with 7-aminoactinomycin D (7-AAD) and analyzed by flow cytometry. Rip-E showed a bactericide effect against Gram-positive species S. aureus and S. epidermidis, as well as, against Gram-negative species Escherichia coli and Salmonella enterica Typhimurium, but was inactive against Pseudomonas aeruginosa. Moreover, Rip-E showed activity against fungi species Candida albicans and C. tropicalis. S. aureus, E. coli and C. albicans cells treated with Rip-E were marked with 7-aminoactinomycin D (7-AAD) indicating that Rip-E can cause plasma membrane damage, acting as a potential microbicide agent for prevention or treatment of infectious diseases.

The "Jack-of-all-Trades" Flagellum From Salmonella and E. coli Was Horizontally Acquired From an Ancestral ß-Proteobacterium.

The γ-proteobacteria are a group of diverse bacteria including pathogenic Escherichia, Salmonella, Vibrio, and Pseudomonas species. The majority swim in liquids with polar, sodium-driven flagella and swarm on surfaces with lateral, non-chemotactic flagella. Notable exceptions are the enteric Enterobacteriaceae such as Salmonella and E. coli. Many of the well-studied Enterobacteriaceae are gut bacteria that both swim and swarm with the same proton-driven peritrichous flagella. How different flagella evolved in closely related lineages, however, has remained unclear. Here, we describe our phylogenetic finding that Enterobacteriaceae flagella are not native polar or lateral γ-proteobacterial flagella but were horizontally acquired from an ancestral ß-proteobacterium. Using electron cryo-tomography and subtomogram averaging, we confirmed that Enterobacteriaceae flagellar motors resemble contemporary ß-proteobacterial motors and are distinct to the polar and lateral motors of other γ-proteobacteria. Structural comparisons support a model in which γ-proteobacterial motors have specialized, suggesting that acquisition of a ß-proteobacterial flagellum may have been beneficial as a general-purpose motor suitable for adjusting to diverse conditions. This acquisition may have played a role in the development of the enteric lifestyle.

Inhibition of the NorA efflux pump of S. aureus by (Z)-5-(4-Fluorobenzylidene)-Imidazolidines.

Searching for new alternatives to antibiotic treatments is crucial to surmount the multidrug-resistant bacteria. In this work, the antimicrobial activity of synthetic imidazolidines was evaluated as well as their modulating effect on the resistance to fluoroquinolones in a S. aureus strain (SA-1199B), which overexpresses the norA gene that encodes the NorA efflux pump. Results showed weak antimicrobial activity (512 µg mL-1) for two fluorobenzylidene derivatives against this bacterial strain, while the other benzylidene derivatives were inactive. Despite this fact, both fluorinated compounds were able to enhance the activity of norfloxacin and ciprofloxacin against SA-1199B up to 6.4- and 3.2-fold, respectively. In addition, both derivatives potentiated the action of ethidium bromide against this strain, suggesting that the modulating effect probably involves the inhibition of the NorA efflux pump, which is in concordance with the fluorimetic assays and molecular docking analyses performed in this work.

Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia.

Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages - archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes - wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.

The Dynamic Roles of the Inner Membrane Complex in the Multiple Stages of the Malaria Parasite.

Apicomplexan parasites, such as human malaria parasites, have complex lifecycles encompassing multiple and diverse environmental niches. Invading, replicating, and escaping from different cell types, along with exploiting each intracellular niche, necessitate large and dynamic changes in parasite morphology and cellular architecture. The inner membrane complex (IMC) is a unique structural element that is intricately involved with these distinct morphological changes. The IMC is a double membrane organelle that forms de novo and is located beneath the plasma membrane of these single-celled organisms. In Plasmodium spp. parasites it has three major purposes: it confers stability and shape to the cell, functions as an important scaffolding compartment during the formation of daughter cells, and plays a major role in motility and invasion. Recent years have revealed greater insights into the architecture, protein composition and function of the IMC. Here, we discuss the multiple roles of the IMC in each parasite lifecycle stage as well as insights into its sub-compartmentalization, biogenesis, disassembly and regulation during stage conversion of P. falciparum.

γ-proteobacteria eject their polar flagella under nutrient depletion, retaining flagellar motor relic structures.

Bacteria switch only intermittently to motile planktonic lifestyles under favorable conditions. Under chronic nutrient deprivation, however, bacteria orchestrate a switch to stationary phase, conserving energy by altering metabolism and stopping motility. About two-thirds of bacteria use flagella to swim, but how bacteria deactivate this large molecular machine remains unclear. Here, we describe the previously unreported ejection of polar motors by γ-proteobacteria. We show that these bacteria eject their flagella at the base of the flagellar hook when nutrients are depleted, leaving a relic of a former flagellar motor in the outer membrane. Subtomogram averages of the full motor and relic reveal that this is an active process, as a plug protein appears in the relic, likely to prevent leakage across their outer membrane; furthermore, we show that ejection is triggered only under nutritional depletion and is independent of the filament as a possible mechanosensor. We show that filament ejection is a widespread phenomenon demonstrated by the appearance of relic structures in diverse γ-proteobacteria including Plesiomonas shigelloides, Vibrio cholerae, Vibrio fischeri, Shewanella putrefaciens, and Pseudomonas aeruginosa. While the molecular details remain to be determined, our results demonstrate a novel mechanism for bacteria to halt costly motility when nutrients become scarce.

Effect of Sweeteners on Root Dentine Demineralization Using a Microcosm Biofilm Model / Efecto de los Edulcorantes en la Desmineralización de la Dentina Radicular Utilizando un Modelo de Biofilm Microcosmo

ABSTRACT: The aim of the present study was to evaluate the effect of commercial sweeteners on root dentin demineralization using a microcosm biofilm model. Bovine dentin specimens with pre-determined surface hardness were randomized into six groups according to the studied sweeteners: sucralose, stevia, saccharin, aspartame. Sucrose was used as a positive control and an untreated group as a negative control. The specimens were submitted to biofilm development from one saliva donor and the cariogenic challenge occurred on subsequent five days, twice a day. At the end, the percentage of surface hardness loss (%SHL) and biomass was determined and submitted to ANOVA followed by Tukey's test. Sucrose presented the highest rate of demineralization, however, all sweeteners tested lead to a statistically higher root demineralization compared to the negative control (p <0.05). Sucrose caused greater demineralization in root dentin, however, the sweeteners were also able to induce it under this biofilm model.

RESUMEN: El objetivo del presente estudio fue evaluar el efecto de los edulcorantes comerciales en la desmineralización de la dentina radicular utilizando un modelo de biofilm microcosmo. Se asignaron al azar muestras de dentina bovina con una dureza de la superficie predeterminada de acuerdo con los edulcorantes estudiados: sucralosa, estevia, sacarina, aspartame. La sacarosa se utilizó como control positivo y un grupo no tratado como control negativo. Las muestras se enviaron al desarrollo de biopelículas de un donante de saliva y el desafío cariogénico se produjo en los siguientes cinco días, dos veces al día. Al final, se determinó el porcentaje de pérdida de dureza de la superficie (% PDS) y biomasa y se aplicó un estudio estadístico de ANOVA seguido de la prueba de Tukey. La sacarosa presentó la mayor tasa de desmineralización; sin embargo, todos los endulzantes probados condujeron a una desmineralización de la raíz estadísticamente mayor en comparación con el control negativo (p<0,05). La sacarosa causó una mayor desmineralización en la dentina de raíz, sin embargo, los edulcorantes también fueron capaces de inducirla bajo este modelo de biofilm.

Giant flagellins form thick flagellar filaments in two species of marine γ-proteobacteria.

Flagella, the primary means of motility in bacteria, are helical filaments that function as microscopic propellers composed of thousands of copies of the protein flagellin. Here, we show that many bacteria encode "giant" flagellins, greater than a thousand amino acids in length, and that two species that encode giant flagellins, the marine γ-proteobacteria Bermanella marisrubri and Oleibacter marinus, produce monopolar flagellar filaments considerably thicker than filaments composed of shorter flagellin monomers. We confirm that the flagellum from B. marisrubri is built from its giant flagellin. Phylogenetic analysis reveals that the mechanism of evolution of giant flagellins has followed a stepwise process involving an internal domain duplication followed by insertion of an additional novel insert. This work illustrates how "the" bacterial flagellum should not be seen as a single, idealised structure, but as a continuum of evolved machines adapted to a range of niches.

Bacterial Flagellins: Does Size Matter?

The bacterial flagellum is the principal organelle of motility in bacteria. Here, we address the question of size when applied to the chief flagellar protein flagellin and the flagellar filament. Surprisingly, nature furnishes multiple examples of 'giant flagellins' greater than a thousand amino acids in length, with large surface-exposed hypervariable domains. We review the contexts in which these giant flagellins occur, speculate as to their functions, and highlight the potential for biotechnology to build on what nature provides.

Communication across the bacterial cell envelope depends on the size of the periplasm.

The cell envelope of gram-negative bacteria, a structure comprising an outer (OM) and an inner (IM) membrane, is essential for life. The OM and the IM are separated by the periplasm, a compartment that contains the peptidoglycan. The OM is tethered to the peptidoglycan via the lipoprotein, Lpp. However, the importance of the envelope's multilayered architecture remains unknown. Here, when we removed physical coupling between the OM and the peptidoglycan, cells lost the ability to sense defects in envelope integrity. Further experiments revealed that the critical parameter for the transmission of stress signals from the envelope to the cytoplasm, where cellular behaviour is controlled, is the IM-to-OM distance. Augmenting this distance by increasing the length of the lipoprotein Lpp destroyed signalling, whereas simultaneously increasing the length of the stress-sensing lipoprotein RcsF restored signalling. Our results demonstrate the physiological importance of the size of the periplasm. They also reveal that strict control over the IM-to-OM distance is required for effective envelope surveillance and protection, suggesting that cellular architecture and the structure of transenvelope protein complexes have been evolutionarily co-optimised for correct function. Similar strategies are likely at play in cellular compartments surrounded by 2 concentric membranes, such as chloroplasts and mitochondria.