Acinetobacter baumannii is an increasingly multidrug-resistant Gram-negative bacterial pathogen and contributes to many hospital-acquired infections. Discovering new treatments against Acinetobacter baumannii infections is necessary as the pathogen adapts to the antimicrobials prescribed by physicians. Cyclic di-GMP (c-di-GMP), a bacterial second messenger, can regulate various phenotypes including biofilm formation, desiccation tolerance, motility, etc.; many of these phenotypes may help A. baumannii better survive a hospital environment, such as dryness on hospital surfaces. Up to twelve c-di-GMP modulating enzymes (CMEs) and two c-di-GMP binding proteins are predicted to be encoded by this pathogen. Diguanylate cyclases (DGCs) produce c-di-GMP, whereas phosphodiesterases (PDEs) degrade c-di-GMP. More c-di-GMP that can bind to its binding proteins means more biofilm formation and less motility. Of the eleven CMEs, 7 are DGCs, 2 are PDEs, and 3 encode both domains (DGCs/PDEs). I hypothesized that biofilm formation, desiccation tolerance, and motility were controlled by c-di-GMP and that we could target these parts of the c-di-GMP signaling network for new treatments. If we disrupt these genes, then we should see a reduction in the regulatory effects of these phenotypes. In this investigation, we generated mutants with a single gene knockout or transposon mutagenesis in two different A. baumannii strains: 17978, a historical laboratory strain that exhibits swarming motility and AB5075, a recent clinical isolate that exhibits twitching motility. To test biofilm formation, we let the mutants grow to their maximum concentration in 96-well plates, stained the plates with crystal violet, and quantified the crystal violet that stained the biofilm. To test for motility, a LB agar plate was stabbed to the plastic surface or dropped on the agar surface with diluted culture to determine the presence of twitching or swarming motility, respectively. To test for desiccation tolerance, we washed the cultures in distilled water to rid the sample of any salt, serially diluted the samples in solution, and plated them out onto LB agar plates. Bacterial counts were quantified before and after desiccation to determine survival of each mutant. From these experiments, 6 DGCs, 1 PDE, and 2 DGCs/PDEs were shown to regulate biofilm formation in AB5075. Furthermore, a PDE and a DGC/PDE were shown to regulate twitching motility in AB5075, while a single DGC was required for tolerating dryness. In strain 17978, we have found a PDE and 4 DGCs that are necessary for swarming motility and are currently conducting biofilm and desiccation tolerance assays. So far, we’ve identified a role for c-di-GMP in A. baumannii biofilm formation, motility, and desiccation survival. Inhibiting the regulation of these pathways could produce novel mechanisms to combat this pathogen in the hospital environment.

Salmonella enterica serovar Typhimurium is one of the most prevalent food-borne pathogens, affecting millions around the world every year, making it a threat to global health. Salmonella possesses the ability to survive the normally lethal condition of desiccation, however, discovery of the genes and mechanisms behind this phenomenon are still ongoing. Using a transposon mutagenesis approach to construct a broad transposon library, this study aimed to uncover genes that may be contributing to changes in Salmonella’s survivability under desiccation, particularly when exposed to the antimicrobial molecule salicylic acid. Building on previous findings showing salicylic acid can alter cell viability through differential gene regulation, transposon mutants were exposed to salicylic acid and subsequently desiccated to screen for mutants that displayed an alteration in survival phenotypes. This work identified a transposon mutant with an interruption of the porin-coding gene ompC that displayed an augmented survivability phenotype under these conditions, leading to further exploration into the origin of this phenomenon.

To persist in extreme environments, some meiofaunal taxa have adopted outstanding resistance strategies. Recent years have seen increased enthusiasm for understanding extreme-resistance mechanisms evolved by tardigrades, nematodes and rotifers, such as the capability to tolerate complete desiccation and freezing by entering a state of reversible suspension of metabolism called anhydrobiosis and cryobiosis, respectively. In contrast, the less common phenomenon of diapause, which includes encystment and cyclomorphosis, is defined by a suspension of growth and development with a reduction in metabolic activity induced by stressful environmental conditions. Because of their unique resistance, tardigrades and rotifers have been proposed as model organisms in the fields of exobiology and space research. They are also increasingly considered in medical research with the hope that their resistance mechanisms could be used to improve the tolerance of human cells to extreme stress. This review will analyse the dormancy strategies in tardigrades, rotifers and nematodes with emphasis on mechanisms of extreme stress tolerance to identify convergent and unique strategies occurring in these distinct groups. We also examine the ecological and evolutionary consequences of extreme tolerance by summarizing recent advances in this field.

Baker's yeast (Saccharomyces cerevisiae) undergoes major biochemical and structural rearrangements in order to survive cycles of desiccation and rehydration, yet a firm understanding of the response is lacking. The purpose of this study was to examine the response of S. cerevisiae to desiccation and rehydration at both the physiological and molecular levels. Transmission electron microscopy was used to show that loss of vacuolar structure, enlarged nuclear boundaries, as well as cell wall thickening were all associated with the desiccation response. Molecular analysis focused on glyceraldehyde-3-phosphate dehydrogenase (GAPDH, E.C. 1.2.1.13), a multifunctional protein that is involved in several cellular processes other than glycolysis, including nuclear translocation under stress and intracellular sensing of oxidative stress during apoptosis. Here, GAPDH was studied primarily to determine its potential role in mediating the changes in cell wall physiology identified through our structural studies. GAPDH appears to be shuttled between the cell wall and the cytoplasm during the desiccation/rehydration process. Western analyses in combination with the use of inhibitors of translation (cycloheximide) suggest that the shuttling process does not require de novo protein synthesis. Western analyses also identified an immuno-reactive peptide in the cell wall and cytoplasmic fractions of lower molecular mass than native GAPDH (27 KDa vs. 37 KDa). This lower molecular weight peptide exhibited the translocation process similar to that of the full length GAPDH. Studies with GAPDH deletion strains suggested that the 27 kDa fragment is encoded by tdh3. The importance of this lower molecular weight form is yet to be determined. / Master of Science in Life Sciences

No / Extant literature contains a number of specific case studies on differential decomposition involving adipocere formation or desiccation, but few describe the co-occurrence of these features within a temperate climate. The case of a 65-year-old male, partially buried in a shallow grave for 7 months, is presented in which the soft tissues of the body were outwardly well preserved. The right leg was desiccated, some parts of the body were covered with adipocere (head, neck, right shoulder, upper torso and left leg) and other parts could be classified as in the early stages of decomposition. In this study the taphonomic variables resulting in differential decomposition with desiccation and adipocere formation are discussed.

A desiccation-tolerant cyanobacterium <i>Nostoc commune</i> accumulates a novel group of water stress proteins (Wsp) in response to cycles of repeated drying and rehydration. Antibodies, specific for Wsp, were used to screen a lambdafix II library of <i>N. commune</i> UTEX 584 Bam H1 DNA fragments and an 8.5-kb fragment, containing a gene cluster that synthesized a 59-kDa cross-reactive protein. The cloned fragment comprised five ORF’s. The ORF’s 59, 24, 22, 36, and 70, each potentially encode products of molecular weights of 59, 24, 22, 36, and 70-kDa, respectively. The 59 and 24 ORF products were found to be expressed in <i>E. coli</i>. The 59-kDa product of this fragment gives the strongest cross-reaction with the Wsp antiserum. The 59-kDa protein was partially purified. The 24-kDa product was successfully purified to homogeneity and partially characterized. This study used <i>E. coli</i> strain DH10B transformed with the pTrc 99A plasmid. The pTre 99A contains the 8.5-kb gene cluster fragment of interest. The products of ORF 24 and 59 were isolated using an initial 40-60 % ammonium sulfate precipitation of a clarified <i>E. coli</i> cell lysate. The clarified cell lysate was then subjected to streptomycin sulfate precipitation. The cell lysate was then dialyzed extensively. The cell lysate was then applied to a Mono Q HR 5/5 anion exchange column using a 2 M KCl gradient elution procedure. The Mono Q column yielded a fraction containing both ORF products which eluted with approximately 400 mM KCl. This fraction was then applied to a Superose 12 HR 10/30 gel filtration column. The eluent fraction containing the ORF 24 product was then reapplied to the Superose 12 to yield the final fraction containing only the ORF 24 product. The final fraction of ORF 24 was purified to homogeneity as determined by SDS-PAGE analysis. Approximately 750 μg of ORF 24 was isolated. This preparation was used for characterization studies. Characterization studies of ORF 24 consisted of an amino-terminal sequence analysis, an estimation of the molecular weight using gel filtration chromatography and SDS-PAGE analysis, and an analysis of enzymatic activity as suggested by amino acid sequence homologies. The amino-terminal sequence of ORF 24 is P V E Q R S H D. The molecular weight of ORF 24 using gel-filtration chromatography and SDS-PAGE analysis is 26-kDa and 23-kDa, respectively. From gene sequence analysis, the molecular weight of ORF 24 is known to be 24,340-Da. These data indicate that ORF 24 is a monomer. ORF 24 was found to have amino acid sequence homologies with a pectate lyase (E 4.2.2.2) periplasmic precursor from <i>Erwinia caratovora</i> subspecies and a dextransucrase (EC 2.4.1.5) precursor from <i>Streptoccocus mutans</i> GS-5. However, pectate lyase activity was not detected in cellular extracts over a 24 hour period. In addition, ORF 24 was not found to interact with 10 % substrate solutions of N-acetylglucosamine, pectin, UTEX 584 sheath material, DRH1 sheath material, sucrose, or glucose using thin layer chromatography. These studies indicate that the enzymatic activities proposed from amino acid sequence homologies have not been detected. The suggestion that ORF 24 is a water stress protein with a protective function on a structural level with regards to desiccation-tolerance requires further study. / Master of Science

Les bactéries du genre Deinococcus sont extrêmement tolérantes à de fortes doses de radiations. Des études antérieures ont montré que IrrE est nécessaire à la radiotolérance et à l'induction des gènes de réparation de l'ADN après exposition des cellules à l'irradiation. Pendant des années il est resté inconnu comment IrrE active l'expression de ces gènes. L'objectif de ma thèse était la caractérisation de la voie de signalisation dépendent de IrrE chez Deinococcus deserti. Pour cela, des approches biochimiques et génétiques ont été utilisées. Les premiers résultats ont fortement suggéré que IrrE agit indirectement sur l'activation de l'expression des gènes. En utilisant des expériences in vitro et in vivo, nous avons montré que IrrE de Deinococcus deserti interagit avec DdrO, un régulateur potentiel qui est codé par un gène radio-induit et qui est, comme IrrE, conservé chez les Deinococcus. De plus, IrrE clive DdrO in vitro mais aussi in vivo lorsque les deux protéines sont co-exprimées chez Escherichia coli. Ce clivage est abolit en présence d'un agent chélateur de métaux, l'EDTA. Chez D. deserti, le clivage de DdrO dépendent de IrrE a été observé mais seulement après exposition à l'irradiation. En parallèle, nous avons montré que la répression du promoteur d'un gène radio-inductible est dépendante de DdrO. Nos résultats montrent donc que IrrE est une métalloprotéase et nous proposons que le répresseur DdrO soit désactivé après clivage par IrrE conduisant à l'induction de différents gènes indispensables pour la réparation de l'ADN et la survie des cellules après exposition de Deinococcus à l'irradiation. / Deinococcus bacteria are famous for their extreme tolerance to high doses of radiation. Earlier studies have shown that IrrE protein is required for radiation tolerance and for induction of DNA repair genes after exposure of cells to radiation. However, for years it has remained unknown how IrrE activates gene expression. The aim of my thesis was to characterize the IrrE-dependent regulation pathway in Deinococcus deserti. For this, biochemical and genetic approaches were used. The first results strongly suggested that IrrE activates gene expression in an indirect manner. Then, using other in vivo and in vitro experiments, IrrE from Deinococcus deserti was found to interact with DdrO, a predicted regulator encoded by a radiation-induced gene that is, like irrE, highly conserved in Deinococcus. Moreover, IrrE was found to cleave DdrO in vitro and also in vivo when the proteins were co-expressed in Escherichia coli. This cleavage was not observed in the presence of the metal chelator EDTA. In D. deserti, IrrE-dependent cleavage of DdrO was observed only after exposure to radiation. Furthermore, DdrO-dependent repression of the promoter of a radiation-induced gene was shown. Our results demonstrate that IrrE is a metalloprotease and we propose that IrrE-mediated cleavage inactivates repressor protein DdrO, leading to transcriptional induction of various genes required for DNA repair and cell survival after exposure of Deinococcus to radiation.

Entre os vegetais existem duas estratégias distintas para superar as condições de estresse hídrico que condicionam a sensibilidade a dessecação (SD) que está associada a mecanismos de evitação e a tolerância a dessecação (TD) que envolve suportar o estresse hídrico diretamente no nível dos tecidos e no nível subcelular. Sabe-se que os custos acoplados aos mecanismos de dessecação e reidratação em espécies TD são elevados, e provavelmente superiores aos de espécies SD. Desta forma, a coexistência de espécies com estas estratégias, como ocorre no ambiente epifítico da Cidade Universitária Armando Sales de Oliveira (CUASO), induzem questões quanto a as vantagens relativas de espécies TD sobre SD. Devido aos altos custos da estratégia TD é possível propor que estas deveriam apresentar um ganho médio de carbono superior a de espécies SD durante o período favorável (com disponibilidade hídrica). Além disso, também é razoável esperar que as distintas formas de uso da água, vinculadas às estratégias, poderiam facilitar o convívio de espécies TD e SD através da segregação de nichos. Com intuito de verificar essas hipóteses, foram realizadas análises relacionadas a estrutura de comunidade de epífitas da CUASO e, a partir destas, a detecção da associação espacial mais freqüente, que resultou composta por Pleopeltis hirsutissima (TD) e Microgramma squamulosa (SD). Estas espécies foram então selecionadas para avaliar parâmetros associados à dinâmica do uso da água, assimilação líquida de carbono, dinâmica da capacidade de uso da luz, estado de hidratação foliar e pigmentos fotossintéticos. Os resultados apontaram que espécies de ambas as estratégias não apresentam sinais de estresse crônico no ambiente estudado. Os dados reforçaram as respostas contrastantes de TD e SD, refletindo as formas distintas de lidar com os recursos e condições do ambiente. Ao contrário do esperado, P. hirsutissima não apresentou uma assimilação de carbono superior a M. squamulosa, indicando que o ganho de carbono não é um dos fatores possíveis na compensação dos custos acoplados a sua estratégia (TD). Porém, os resultados apresentados quanto a dinâmica da capacidade de uso da luz sugerem que a coexistência é facilitada pela segregação de nichos de luz, sendo a espécie TD mais heliófila do que a espécie SD / In land plants the resistance to drought can be accomplished by two main strategies. One involves mainly dehydration avoidance mechanisms and the other is based on the ability to withstand drought at the tissues and down to subcellular levels. The former is found on the desiccation sensitive plants (DS) and the last describes the desiccation tolerant plants (DT). The metabolic costs of the desiccation tolerance mechanisms are probably high, at least when considering the cessation of photosynthesis during anabiosis - a condition that is absent in drought avoidance strategies. The coexistence of drought avoiders and desiccation tolerant plants in the same substrate and condition can rise some questions about the relative advantages of each strategy when submitted to similar water regime. We ask whether desiccation tolerant plants have a compensatory carbon gain under a watering regime that induces frequent anabiosis or cumulative damage in drought avoidance have a detrimental effect comparable to the costs of the desiccation tolerance. An analysis of the epiphytic plant community associated to the trees of the CUASO urban landscape showed a very frequent co-occurring species pair including the desiccation sensitive Microgramma squamulosa and a desiccation tolerant Pleopeltis hirsutissima, both cryptogams of the same plant family. These species were thoroughly examined regarding the patterns of light, water and carbon dynamics together with pigments concentration during cycles of natural drought and wet climate field conditions. These observations were complemented with experimental induction of different water and light regimes. The results showed no sign of chronic stress in both plants living at the same condition but allowed us to identify large distinctions in resource use patterns. A compensatory carbon assimilation was not found in P.hirsutissima. Both species have similar CO2 assimilation values. Experimental induction of drought in different light regimes allowed to verify a relative advantage in desiccation tolerant P.hirsutissima in comparison to the desiccation sensitive M.squamulosa under high irradiance values. Furthermore, light curve analysis suggest that they share the same tree but their niches differ in light intensity regime allowing the high frequency of co-occurrence observed in the field

Neste trabalho caracterizamos o nematoide Panagrolaimus sp. linhagem CEW2, originalmente isolado em Monte Negro (RO), Brasil e mantido em nosso laboratório em culturas monoxênicas contendo Escherichia coli. CEW2 se mostrou um nematoide extremófilo capaz de sobreviver ao dessecamento em 10% de umidade relativa por pelo menos 48h. Essa resistência é mais evidente em larvas de primeiro estádio (L1) do que em adultos ou larvas dauer. Quando pré-incubados por 48h em 98% de umidade relativa a sua resistência ao dessecamento aumenta e pode chegar a uma sobrevivência de 86,25% dos indivíduos no caso de L1. Os animais dessecados se tornam também resistentes ao congelamento. Os indivíduos pré-incubados em 98% de umidade relativa tornam-se resistentes ao congelamento. O retorno à atividade após secagem ou congelamento ocorre de maneira diferente dependendo da concentração de NaCl no meio, sugerindo que eles sejam, além de anidrobiontes e criobiontes, sejam também osmobiontes. Um outro aspecto da fisiologia de CEW2 que também começamos a caracterizar é a composição de polipeptídeos das vitelinas de seus ovos. SDS-PAGE das proteínas presente em ovos de CEW2 apresentam 6 bandas principais coradas por Coomassie Blue (com Mr que variam de 85 a 125 kDa), 3 a mais do que aquelas detectadas nos outros dois nematoides cujas vitelinas foram caracterizadas, Caenorhabditis elegans e Oscheius tipulae. Quando comparamos as vitelinas destas três espécies notamos que CEW2 não possui a vitelina de 180 kDa (YP170A e B de C. elegans e VT1 de O. tipulae). Essa análise comparativa das vitelinas de nematoides nos permitiu propor um esquema para a origem das três bandas extras detectadas em CEW2. Não foi possível purificar as vitelinas de CEW2 usando o mesmo protocolo que desenvolvemos para as vitelinas de O. tipulae e C. elegans. Isso se deve a uma atividade proteolítica presente nos homogeneizados de vermes que co-purifica com as vitelinas e leva a sua degradação durante a armazenagem. As atividades proteolíticas presentes nesses homogeneizados foram caracterizados por zimografia e foi possível purificar uma das bandas que cremos ser uma protease digestiva de CEW2 e a responsável pela degradação das vitelinas purificadas. / In this work we characterize some survival and reproductive strategies of the nematode Panagrolaimus sp., strain CEW2. CEW2 was originally isolated in Monte Negro (RO), Brazil. CEW2 is currently maintained in monoxenic cultures with E. coli in our laboratory and has proved to be an extremophile that survives desiccation at 10% relative humidity for at least 48 hours. First instar larvae (L1) are more resistant to desiccation than adults or dauer larvae. When pre-incubated for 48 h at 98% relative humidity their resistance to desiccation increases and can reach a survival rate of 86,25 % with L1individuals. The dried animals also become resistant to freezing. Worms that were pre-incubated at 98% relative humidity become resistant to freezing in water at -20 °C. The return to activity upon drying or freezing occurs differently depending on the NaCl concentration in the medium, suggesting that CEW2 is an osmobiont in addition to its anidrobiotic and criobiotic behavior. We also began to characterize another aspect of CEW2 physiology; the polypeptide composition of the vitellins in their eggs. SDS-PAGE of the proteins present in CEW2 eggs show 6 major Coomassie Blue stained bands (Mr ranging from 85-125 kDa), three more than those detected in the vitellins of Caenorhabditis elegans and Oscheius tipulae. When we compare the vitellins of these three species we notice that CEW2 lacks the yolk proteins of 180 kDa (YP170A and B present in C. elegans and VT1 in O. tipulae). The comparative analysis of nematode vitellins allowed us to propose a model for the origin of the three extra bands detected in CEW2. We propose that in CEW2 the polypeptides that are ortologous to the 180 kDa polypeptides of C. elegans and O. tipulae, suffer a proteolytic cleavage similar to that occurring with the precursor of YP115 and 88 in C. elegans. It was not possible to purify the vitellins of CEW2 using the same protocol developed for the vitellins of O. tipulae and C. elegans. This is due to a proteolytic activity present in homogenized worms which co-purifies with the vitellins and leads to their degradation during the procedure. Proteolytic activities present in these homogenates were characterized by zymography and it was possible to purify one of the bands that we believe to be a digestive protease from CEW2 responsible for the degradation of purified vitellins.

Diversas espécies de anuros da família Leptodactylidae se reproduzem em corpos dágua sazonais, temporários e mantidos exclusivamente por chuvas. Em períodos de estiagem prolongada a poça pode secar completamente, ocasionando elevadas taxas de mortalidade de ovos e girinos dessas espécies, podendo exercer forte pressão seletiva na evolução de mecanismos de resistência e sobrevivência nas fases iniciais do desenvolvimento. Algumas espécies de girinos conseguem sobreviver cerca de cinco dias fora dágua o que pode proporcionar uma adaptação vantajosa, porque possibilita a sobrevivência dos girinos por um período que pode ser suficiente para a reincidência de novas chuvas e restabelecimento do corpo dágua. Apesar dessa capacidade de sobrevivência, pouco se sabe sobre as possíveis modificações que a desidratação pode causar na locomoção e na morfologia durante o desenvolvimento desses animais. O presente trabalho teve como objetivo avaliar o efeito do estresse hídrico: (1) no nível de sobrevivência e perda de massa corpórea; (2) no desempenho locomotor; (3) na morfologia externa (morfometria linear) e interna, analisando tanto o volume total quanto o volume visceral (estereologia); e (4) no tempo até metamorfose após o estresse. Utilizamos girinos de duas espécies de anuros, Leptodactylus fuscus (Leptodactylinae) e Physalaemus nattereri (Leiuperinae), ambas as espécies se reproduzem em corpos dágua temporários, em áreas com estação seca definida estando, portanto sujeitas as mesmas pressões seletivas. Além disso, as duas espécies apresentam modos reprodutivos diferentes, podendo apresentar diferentes graus de resistência ao estresse hídrico. Os girinos das duas espécies foram divididos em dois grupos, os que ficaram em água (grupo controle) e os que foram submetidos ao estresse hídrico (grupo tratamento), por três períodos de tempo (12, 24 e 72 horas). Houve diferenças significativas para valores de perda de massa entre os grupos controle e tratamento em ambas as espécies, sendo o grupo tratamento que mais perdeu massa corpórea em todos os períodos, além disso, quase metade dos girinos de P. nattereri morreram em 36 horas de estresse. Não houve diferenças significativas para os dados de desempenho locomotor e volume total entre os grupos testado para girinos de L. fuscus, mas houve diferenças morfometricas significantes nos componentes relacionados a cauda e no volume visceral, onde, o intestino do grupo tratamento foi menor que do controle. Já em P. nattereri, houve diferenças significativas entre os grupos testados para desempenho locomotor, volume total, morfometria da cauda e volume visceral, sendo o estomago e anexo do tratamento maior que do controle. Nossos resultados sugerem que a exposição ao estresse hídrico não afeta significativamente a morfologia e o desempenho locomotor dos girinos de L. fuscus. No entanto, girinos de P. nattereri apresentaram uma sensibilidade ao estresse hídrico prolongado, principalmente sobre o seu desempenho locomotor. / Several species of frogs (Leptodactylidae) breed in temporary pools maintained exclusively by rainfall. These pools easily dry out causing high mortality of eggs or tadpoles thereby possibly exerting strong selective pressure on the evolution of resistance mechanisms and survival in the early stages of development. However, the tadpoles of some species can survive up to five days in pools that are drying out, needing only a humid substrate for development which can provide an advantageous adaptation, because it enables the survival of tadpoles for a period that may be enough for the recurrence of new rains and restoration of the water body. Despite this ability to survive out of water, it is not known which possible damages dehydration stress causes in tadpoles during their ontogeny. The aim of this study was to evaluate the effect of hydric stress on: (1) the level of survival and weight loss; (2) locomotor performance; (3) external (linear morphometry) and internal morphology, analyzing the total volume and visceral volume (stereology); and (4) the time of development after stress. We used tadpoles of two species, Leptodactylus fuscus (Leptodactylinae) and Physalaemus nattereri (Leiuperinae), both species breed in temporary ponds in areas with well-defined dry season therefore these species are subject to the same selective pressure. In addition, the two species show different reproductive modes, and may possess different degrees of resistance to water stress. To this end, the tadpoles were divided into two groups, those who stayed in 100 ml of water (control group) and those that were subjected to hydric stress (treatment group) for three time periods (12, 24 and 72 hours). Significant differences for weight loss were found between the groups (control/treatment) in both species, with the treatment group losing more weight in all stress levels. Furthermore almost half of P. nattereri tadpoles died within 36 hours of stress. There was no significant difference for locomotor performance and total volume between control group and treatment group of L. fuscus tadpoles, but morphometric analyses indicated a significant difference in the components related to tail and visceral volume, with the gut of the treatment group was lower than the control. In P. nattereri tadpoles, there were significant differences between the groups tested for locomotor performance, total volume, tail morphometry and visceral volume, with the stomach of the treatment group being greater than in the control group. Our results suggest that hydric stress has a significant effect on locomotion and morphology of P. nattereri tadpoles, but not in L. fuscus.