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metazoan
metazoa

metazoan parasite
parásito metazoario

parasite, metazoan
metazoa

metazoan parasite, nos
parásito metazoario

metazoan parasite (organism)
metazoa

the metazoan food webs from six bornean "nepenthes" species.
the metazoan food webs from six bornean "nepenthes" species.

the default state of cell proliferation in metazoan (animal life) is quiescence
el estado por defecto de la proliferación celular en metazoos (vida animal) es quiescencia

this protein has not been found in yeast, which suggests that it is likely to have an abnormal exonuclease domain like the one seen in a metazoan.
esta proteína no ha sido encontrada en levaduras, lo que sugiere que es probable que ccr4 posea un dominio exonucleasa anormal como la que se observa en los metazoos.

the effects of pitcher dimorphism on the metazoan community of the carnivorous pitcher plant "nepenthes bicalcarata" hook.f.
the effects of pitcher dimorphism on the metazoan community of the carnivorous pitcher plant "nepenthes bicalcarata" hook.f.

some forms of polymetallic nodules are also inhabited by diverse organisms, including bacteria, protozoa and metazoan, which constitute another layer of species richness, or yet another reservoir of species diversity.
algunas formas de nódulos polimetálicos también están habitados por diversos organismos, incluidos bacterias, protozoarios y metazoarios, que constituyen otra capa de riqueza biológica, un reservorio más de biodiversidad.

pahomtsstudying host–microbiota mutualism in drosophila: harnessing the power of gnotobiotic flies dali ma, gilles storelli, mélanie mitchell, françois leulier the complex interaction between the metazoan host and its commensal gut microbiota is one of the essential features of symbiosis in the animal kingdom. as there is a burgeoning interest to decipher the molecular dialog that shapes host microbiota mutualism, the use of gnotobiotic model organism becomes an imperative approach to unambiguously parse the specific contributions to such interaction from the microbiome. in this review, we focus on several remarkable gnotobiotic studies in drosophila that functionally depicted how the gut microbes can alter host physiology and behavior through transcriptomic regulation, hormonal control, and diet modification. these results in concert illustrate that the gnotobiotic flies mono or poly associated with members of its gut microbiota deliver a versatile and powerful model that is amenable to different types of studies ranging from classic genetics to large scale systems approaches.(biomed j ????;??:?? ??). in 1883, louis pasteur expressed his wish to raise a “micro¬bially deprived” young animal on “pure” food from birth, and postulated that “without any preconceived notion…. life under such condition… shall become impossible.”[1] nearly 30 years later, eugene wollman at the pasteur institute in paris successfully cultured the first germ free common blow flies (calliphora vomitoria) and observed that except for certain minor growth delay, the adult flies appeared perfectly normal.[2] at first, wollman’s experiment seemed to have put an end to pasteur’s claim; yet in truth, it was only the begin¬ning. throughout his productive career as a microbiologist, wollman probably did not realize that his germ free blow flies spawned an entire field of animal physiology based on host–microbe interactions; and only when a germ free life was made possible, the concept of “gnotobiology” could spring to life. in the past century, pasteur’s musing on what life would be like without its resident microbes gradually transformed to a quest to understand how the eukaryotic hosts and their bacterial partners orchestrate the symphony of life, and how such interactions probably profoundly altered the course of our evolutionary history.[3] microbes occupy every possible ecological niche on earth. a set of particular niches comprise the various inter¬nal epithelia of the metazoan hosts, who, through eons of evolution, have forged complex and intricate relationships with this rich and diverse microbial community, called the “microbiota”[3,4] a human host carries on his body far more microorganisms than his own cells, and these invisible dwellers constitute 1–3% of his body mass.[5,6] the human gut alone harbors approximately 500–1000 bacterial spe¬cies,[7] and represents the largest mucosal surface where the exchanges between the host and the microbiota take place. in the last decades, many studies together generated a systematic understanding of how the gut microbiota and its diverse gene repertoire, called the “microbiome”, can configure the fitness parameters of the host; a healthy mi-crobiota can expand the host’s metabolic potential, fortify its immune system, promote healthy aging, and even dictate its emotional and psychological well being.[6,8 11] however, as the community structure and activities of the gut microbiota are extremely sensitive to fluctuations in the environment, perturbations to the microbiota pose significant risks to the host.[12,13] subtle changes in host immunity, diet, or xeno¬biotic concentration can disrupt the balance in the gut mi-crobial community, which consequently compromises host fitness. in mammals, microbiome imbalance, or dysbiosis, positively correlates with the onset of obesity, diabetes, colon cancer,[14 16] and human psychiatric disorders such as schizophrenia and autism.[17] currently, a large amount of research on host–microbiota mutualism employs vertebrate models, yet the high complexity of the microbial composition in the mammalian gut, the dif¬ficulty to culture most of these microbial species, and the cost of raising these animals in a strictly sterile environment pose a considerable obstacle. therefore, to delve deeper into the molecular interplay between the host genome and the micro¬biome and the environmental contributions to such interplay, a more genetically tractable model organism with simpler and even defined microbiota is an attractive option. drosophila melanogaster fits these criteria. first of all, the intestinal tract of the fruit fly is anatomically and physiologically similar to the mammalian gut;[18] yet the microbial composition is rather simple: throughout the larval and adult life, the fly gut hosts five to twenty aero tolerant commensal species, all of which are readily cultured in the laboratory.[19,20] two families of bacteria: acetobacteraceae and lactobacillaceae, dominate the community.[21 26] however, the fly gut microbiota is tran¬sient in nature and requires constant replenishment; thus, the community structure and bacterial load fluctuate highly as the flies develop and age.[27 29] such inconstancy makes it difficult to clearly pinpoint the bacterial genetic factors contributing to host physiology. therefore, the use of gnotobiotic fly models, in combination with classic genetic approaches and next generation sequencing, proves to be the new and effective means to study intestinal mutualism with added advantage, because it enables the investigators to inoculate the germ free subjects with various bacterial strains of predefined quantity and composition, such as any member of the fly microbiota. in this setting, the researchers not only can rigorously monitor the phenotypic changes in different aspects of host physiology, but also can robustly correlate and even attribute particular changes to the specific functions from the microbiome, as the genomes of many gut microbiota species are being rapidly sequenced and annotated.[5] moreover, except for acetobacter, which are mostly found in insects,[30,31] lactobacillus species are commensal to mammals.[32 34] therefore, the results from such gnotobiotic fly studies can be readily translated to mam¬malian studies. drosophila models were first used to dissect the genetic networks governing host–pathogen interaction (see review by el chamy et al. in the same issue). with the same approach, pioneering studies have shown promising results to identify and functionally characterize the genetic compo¬nents of the molecular crosstalk between drosophila and its commensal bacteria. in this review, we discuss the findings from the studies using gnotobiotic fly models to unravel the impact of the members of gut microbiota on host metabolism, physiology and behavior [figure 1]. the making of the gnotobiotic flies as mentioned before, in the early 1910s, eugene woll¬man and his colleagues at the pasteur institute were among the first to raise germ free animals such as common blow flies, tadpoles, and guinea pigs. wollman made the first germ free common blow flies by treating the egg surface with diluted hydrogen peroxide and raising the larvae on sterilized meat substrate.[2] interestingly, wollman observed that the germ free larvae reached normal body size, but at a slower rate. moreover, these flies seemed slower in move¬ment and less interested in foraging. therefore, even though the “microbially deprived” life was indeed possible in a sterile environment, the difference between such a life and its conventionally reared (cr) siblings was already observ¬able to the naked eye. in the next few decades, drosophila melanogaster was attaining a more and more prominent status as a model genetic organism. as a result, in the 1950s and 1960s, different methods were developed to sterilize drosophila eggs on a large scale and keeping axenic fly stocks turned into a routine laboratory practice. in 1969, marion bakula developed the first monoxenic drosophila model by associating bleached fly eggs with either “native” or “foreign” bacterial strains (escherichia coli).[35] in her study, only the “native” bacteria isolated from the fly gut persisted throughout larval development in the fly host, who pupariated at a slightly faster pace than the axenic controls. this is also the first gnotobiotic model to demonstrate that the essential mode of microbial transmission in fruit flies is through larval ingestion of the contaminated chorion. there¬fore, thorough dechorionation of the eggs can effectively render a fly stock germ free. in the next several decades, after trying different sterilizing agents such as antiformin and formalin,[36] researchers found that treatment with common household bleach (diluted sodium hypochloride solution) in combination with ethanol wash is the safe, simple, rapid and effective way to dechorionate the embryo and rid the surface of bacterial “contaminants”. however, bleaching alone cannot eliminate intracellular endosymbionts such as wolbachia, the most widespread insect symbiont whose relationship with the host ranges from parasitism to mutualism. depending on the context, the presence of wolbachia is known to affect reproductive success, enhance insulin signaling and boost host defense.[37 40] therefore, to obtain a “true” germ free or gut commensal specific phenotype unadulterated by wolba¬chia, different laboratories have adopted various protocols to maintain germ free stocks, either by combining bleaching with rearing flies on food containing a mixture of antibiotics or by one time treatment of bleach and the subsequent mainte¬nance of the flies in a sterile environment [figure 1a]. of note, bleaching and/or antibiotic treatment can lower fly viability and fecundity and have certain unintended negative cellular and systemic effects on the host.[41] therefore, the studies us¬ing germ free flies mandate careful and thorough controls. in the following sections, we review a few seminal gnotobiotic drosophila studies that have uncovered important molecular mechanisms governing host–microbiota interaction. figure 1: building a gnotobiotic drosophila model to study host–microbiota mutualism. (a) to obtain germ free flies, freshly laid eggs are harvested in a large scale and washed in succession with bleach, ethanol, and sterile water. to maintain axeny, the dechorionated eggs are then grown in the presence of antibiotics and preservatives or in a sterile environment. (b) to study the specific contribution of the microbiome to the different aspects of host physiology, ex axenic eggs or adults are mono associated with a single gut commensal species (green drop) or poly associated with a defined set of gut commensal bacteria (blue and yellow colored drop). such gnotobiotic flies have been used to study the impact of specific commensals on host juvenile growth, developmental timing, metabolic homeostasis, and adult behavior. the study of host physiology using gnotobiotic fly model a gnotobiotic fly model with classic genetics approach that the germ free flies develop and grow at a slower pace is an old observation that has held true since wollman’s time. for example, in baluka’s monoxenic culture, the native bacterial isolates from the drosophila gut, stock 13, a brevi¬bacterium variant, accelerated pupariation compared to the axenic stock.[35] this observation has now been further char¬acterized in greater detail. on a “standard” laboratory diet, the pupariation and adult eclosion rate of the axenic flies are delayed by one day compared to their cr siblings.[23,42] however, this delay becomes striking when the axenic flies are presented with nutritive challenges. particularly, when raised on a diet where the yeast content was below 0.1%, or was completely replaced by casamino acids, the germ free flies died.[23] this observation suggests that an intact gut microbiota provides life sustaining factors for the host ex¬periencing severe nutritive duress. next, when fed on a diet with low yeast content, germ free flies pupariate six days later than the cr flies.[24] therefore, the gut microbiota can also override the developmental delay to potentiate growth in suboptimal nutritive environment. importantly, these two studies also demonstrated that inoculating the axenic fly embryos with one or several defined gut commensal species, such as lactobacillus plantarum (l. plantarum) or aceto¬bacter pomorum (a. pomorum), can recapitulate the growth benefits conferred by the entire gut microbiota. moreover, only certain strains of l. plantarum sustain growth on a low yeast diet; several other isolates from the fly origin were unable to promote host growth even though they could colonize the larval gut and the fly food just as efficiently as the beneficial strains.[24] this observation unequivocally illustrates that the gut microbiota promotes growth by not just serving as a food source, but through complex molecular and biochemical interactions with the host. how then, does the gut microbiota promote host growth? first of all, like for many metazoan species, the source of the fly gut bacteria comes from contaminated food,[19,29] and naturally, some of the primary functions of the gut bacteria are to enhance digestion and expand the host’s metabolic potential. the additional enzymatic activities of bacterial origin help break down the specific nutritive sub¬strates that are otherwise indigestible for the host, who can in turn harvest energy from these food substrates and extract necessary metabolic building blocks for various biological processes.[6] in addition, essential micronutrients derived from bacterial metabolism, such as vitamins and short chain fatty acids, directly fuel the host’s metabolism.[43] indeed, two recent studies found that fortifying the food fed to the germ free flies with b vitamins phenocopies the effect of the presence of the gut bacteria to a large extent, indicating that the gut microbiota accomplishes metabolic sparing of the b vitamins for the host through a yet unknown mechanism.[42,44] however, the growth benefits from the gut microbiota are probably beyond vitamin b provision. to identify the microbial factors that can rescue host lethality on the ca¬sein diet, shin et al. conducted a random mutagenesis in a. pomorum and isolated strains that restored ex germ free larval survival on casamino acid diet but led to delayed pupariation when compared to animals mono associated with the wild type a. pomorum. several such mutations affect pyrroloquinoline quinone dependant alcohol dehy¬drogenase (pqq adh), an enzyme involved in the ethanol respiratory chain and whose end product is acetic acid. although pqq adh mutant bacterial strains were impaired in their production of acetic acid, supplementation of casamino acid diet with acetic acid alone failed to rescue germ free larval lethality. however, concomitant association with pqq adh mutant a. pomorum strains and supplementation with acetic acid completely rescued larval developmental timing. therefore, upon severe nutritive challenge, the addi¬tion of a. pomorum first and foremost restores the viability of the fly host, and then the intact activity of the bacterial ethanol respiratory chain promotes host growth and matu¬ration. based on this result, it is likely that the molecular mechanisms that sustain larval life and promote growth are separable. genetic factors from the host what are the host factors responding to the beneficial growth promotion effect of the microbiota in the presence of nutritional challenges? the studies of shin et al. and storelli et al. demonstrate that the addition of a. pomorum or l. plantarum can accelerate growth and maturation by modulating host systemic hormonal signaling. in the shin et al., study, larvae mono associated with the pqq adh mu¬tant strain of a. pomorum survived to adulthood, but dis¬played metabolic features reminiscent of defective insulin/ insulin like growth factor (iis) signaling, such as low body weight, retarded growth, elevated hemolymph glucose and trehalose levels, and higher level of triacylglyeride (tag), the main form of stored lipids. at the molecular level, in the fat body of the flies mono associated with mutant pqq adh a. pomorum strains on the casamino diet, membrane activa¬tion of phosphoinositide 3 kinase (pi3k) and cytoplasmic retention of dfoxo were abolished, and the expression of insulin like peptides (dilps) such as dilp3 and 5 was reduced in the larval brain. most importantly, the ectopic expression of dilp2 largely rescued both the defective iis phenotype and the molecular signatures associated with such defects in flies mono associated with mutant strain of a. pomorum. therefore, a. pomorum, partly via its ppq adh activity, regulates iis to maintain the host’s metabolic homeostasis [figure 2]. similarly, on a low yeast diet, mono association with l. plantarum lowered the expression of insulin re¬ceptor, a negative readout of pathway activity, suggesting that the presence of l. plantarum also enhances insulin signaling.[24] moreover, l. plantarum reduced the juvenile growth period through target of rapamycin (tor) signaling: dampening tor activity in the fat body – the functional analogue of the mammalian liver – and the prothoracic gland compromised the l. plantarum growth promoting effect as measured by adult emergence [figure 2]. tor is the host nutrient sensitive signaling pathway devoted to balance organismal growth and maturation in a nutrient dependent manner.[45,46] in the developing larvae, tor activity in the prothoracic gland directly controls ecdysone production, which in turn affects the parameters of systemic growth via iis. as tor responds to the circulating levels of different micronutrients in the hemolymph, such as branched chain amino acids, l. plantarum may act upstream of tor in several ways. first, l. plantarum can directly regulate tor activity by making certain metabolites or other biochemi¬cal pathway intermediates and/or end products. secondly, l. plantarum can either modify the diet or boost the host’s digestive capacity to enhance nutrient assimilation, which then indirectly activates tor pathway. therefore, how l. plantarum promotes host juvenile growth is yet to be studied in detail. now two groups have demonstrated that specific strains from both acetobacter and lactobacillus families can pro¬mote juvenile growth upon nutritive challenge. what effect does the combined action of acetobacter and lactobacillus have on the host? to study how these two commensal bacte¬ria interact in the host and how such interactions impact adult host physiology, a study by newell and douglas compared differences in circulating glucose levels, tag contents, and adult body weight between axenic flies and ex germ free flies associated with a single or different combinations of the five fly commensal species.[47] specifically, using a set of defined microbiomes with up to five commensal spe¬cies (a. pomorum, acetobacter tropicalis, l. plantarum, lactobacillus brevis, and lactobacillus fructivorans), the authors inoculated the germ free flies with one or different combinations of these strains and found that all these com-binations lowered the circulating glucose concentrations in comparison to axenic flies. however, in terms of lowering host tag levels, these different combinations of bacteria worked with different efficiency. the lactobacillus species could lower the tag level moderately; acetobacter did so more effectively than lactobacillus, but was not as effec¬tive as the five species co inoculation, which was the only treatment that recapitulated the benefits of the conventional commensal flora. interestingly, one specific c
pahomts