Análise do transcriptoma de A. molluscorum Av27 após exposição ao TBT

Mestrado em BiotecnologiaO tributilestanho (TBT) é um composto tóxico com efeitos nefastos para o ambiente. Este composto foi utilizado durante vários anos como componente de tintas anti-vegetativas aplicadas nos cascos dos barcos sendo, por isso, reconhecido mundialmente como uma das fontes de contaminação de ambientes aquáticos. Atualmente, o uso destas tintas está proibido em alguns países, verificando-se uma diminuição na concentração de TBT no ambiente. Apesar disso, devido à estabilidade e persistência deste composto (principalmente nos sedimentos), a poluição por TBT continua a ser preocupante. Aeromonas molluscorum Av27 foi isolada no sedimento da Ria de Aveiro, num local contaminado por TBT. Esta bactéria é tolerante a concentrações elevadas de TBT (até 3 mM) e é capaz de degradar o composto nos seus derivados menos tóxicos, DBT e MBT. Com o intuito de conhecer o(s) mecanismo(s) molecular(es) que estão na base destas propriedades, procedeu-se à análise do transcriptoma desta estirpe por pirosequenciação. Para isso, para além da condição controlo (sem TBT), as células foram expostas a 5 e 50 μM de TBT até atingirem o meio da fase exponencial. A validação dos resultados de pirosequenciação foi feita por PCR em tempo real. De uma forma geral, a análise dos transcriptomas de A. molluscorum Av27 revelou a presença de diversos genes sobre-expressos após exposição ao TBT. Os genes que se relacionam com a atividade enzimática e o transporte/ligação de compostos foram aqueles que sofreram maiores alterações a nível de expressão, propondo-se desta forma o seu envolvimento nos mecanismos de resistência e degradação de TBT. Alguns dos genes sobre-expressos identificados codificam para bombas de efluxo e outras proteínas envolvidas na resistência a antibióticos e metais pesados, corroborando a relação entre a resistência a estes compostos e a resistência ao TBT. Para além disso, foi sugerido que proteínas envolvidas na resposta ao stress térmico podem também desempenhar um papel importante na resistência ao TBT. Tendo em conta a análise feita, não foi possível encontrar uma proteína responsável pela degradação do TBT. No entanto, foram detetadas várias proteínas sobre-expressas de função desconhecida. A anotação destas proteínas é de grande importância, uma vez que poderá contribuir para a elucidação do mecanismo de degradação de TBT nesta bactéria. Em estudos anteriores, demonstrou-se que o gene sugE está envolvido no mecanismo de resistência ao TBT em Av27 e que o seu nível de expressão está dependente da fase de crescimento das células. No presente estudo, foi possível confirmar que o gene sugE é sub-expresso na presença de TBT quando as células atingem a sua fase exponencial. Foi ainda possível notar que genes relacionados com a transcrição estão sub-expressos após exposição ao TBT, indicando que este composto afeta a transcrição genética. O estudo detalhado dos genes identificados neste trabalho, potencialmente envolvidos no mecanismo de resistência e/ou degradação do TBT, poderá contribuir para a compreensão destes mecanismos em A. molluscorum Av27, assim como noutros organismos procariotas.Tributyltin (TBT) is a toxic compound with a negative impact to the environment. This compound was used for several years as a component of antifouling paints applied to ship hulls, thus contaminating several aquatic environments worldwide. Currently, the use of these paints is prohibited in several countries, and there has been a consequent decrease of TBT concentration in the environment. However, due to the stability and persistence of the compound (mainly in the sediments), TBT pollution remains a serious problem. Aeromonas molluscorum Av27 was isolated in the sediments of Ria de Aveiro, in a TBT contaminated site. This bacterium is tolerant to high TBT concentrations (up to 3 mM) and is able to degrade it into the less toxic compounds DBT and MBT. In order to better understand the molecular mechanism(s) conferring these properties, a transcriptome analysis was carried out. In addition to the control (without TBT), the cells were grown to the mid-log phase in presence of different TBT concentrations (5 and 50 μM). Pyrosequencing analysis was performed in each of the samples. Validation of the transcriptome results was performed by quantitative real-time PCR. The analysis of the transcriptomes of A. molluscorum Av27 revealed that several genes were up-regulated following exposure to TBT. Genes responsible for enzymatic activities and transport/binding were the most affected by TBT exposure and thus, those genes seem to be involved in TBT resistance and degradation. Some efflux pumps and other proteins involved in resistance to antibiotics or heavy metals were found over-expressed when Av27 cells were exposed to TBT, supporting the relationship between the resistance to these compounds and resistance to TBT. Furthermore, a possible role of heat-shock proteins in TBT resistance in A. molluscorum Av27 was also suggested. So far, the analysis of the transcriptome didn’t allow the identification of the protein responsible for TBT degradation in A. molluscorum Av27. However, several proteins of unknown function were over-expressed in the presence of the toxic compound. The annotation of such proteins is important, since it might help to elucidate the TBT degradation mechanisms in this bacterium. Previous studies demonstrated that the sugE gene is involved in TBT resistance in Av27 strain, and that its’ expression levels depend on the growth phase. Likewise, in the present study, the sugE gene was over-expressed when the cells were grown to the mid-log phase. It was also verified that several transcription-related genes were under-expressed in A. molluscorum Av27 following exposure to TBT, suggesting that this compound negatively affects genetic transcription. Further investigation of the genes potentially involved in TBT resistance/degradation may contribute to a better understanding of these mechanisms in A. molluscorum Av27, as well as in other prokaryotes

Integrated biomarker responses of an estuarine invertebrate to high abiotic stress and decreased metal contamination

An integrated chemical-biological effects monitoring was performed in 2010 and 2012 in two NW Iberian estuaries under different anthropogenic pressure. One is low impacted and the other is contaminated by metals. The aim was to verify the usefulness of a multibiomarker approach, using Carcinus maenas as bioindicator species, to reflect diminishing environmental contamination and improved health status under abiotic variation. Sampling sites were assessed for metal levels in sediments and C. maenas, water abiotic factors and biomarkers (neurotoxicity, energy metabolism, biotransformation, anti-oxidant defences, oxidative damage). High inter-annual and seasonal abiotic variation was observed. Metal levels in sediments and crab tissues were markedly higher in 2010 than in 2012 in the contaminated estuary. Biomarkers indicated differences between the study sites and seasons and an improvement of effects measured in C. maenas from the polluted estuary in 2012. Integrated Biomarker Response (IBR) index depicted sites with higher stress levels whereas Principal Component Analysis (PCA) showed associations between biomarker responses and environmental variables. The multibiomarker approach and integrated assessments proved to be useful to the early diagnosis of remediation measures in impacted sites

N-acetyl-β -d-glucosaminidase activity in feral Carcinus maenasexposed to cadmium

Cadmium is a priority hazardous substance, persistent in the aquatic environment, with the capacity to interfere with crustacean moulting. Moulting is a vital process dictating crustacean growth, reproduction and metamorphosis. However, for many organisms, moult disruption is difficult to evaluate in the short term, what limits its inclusion in monitoring programmes. N-acetyl-β-d-glucosaminidase (NAGase) is an enzyme acting in the final steps of the endocrine-regulated moulting cascade, allowing for the cast off of the old exoskeleton, with potential interest as a biomarker of moult disruption. This study investigated responses to waterborne cadmium of NAGase activity of Carcinus maenas originating from estuaries with different histories of anthropogenic contamination: a low impacted and a moderately polluted one. Crabs from both sites were individually exposed for seven days to cadmium concentrations ranging from 1.3 to 2000 μg/L. At the end of the assays, NAGase activity was assessed in the epidermis and digestive gland. Detoxification, antioxidant, energy production, and oxidative stress biomarkers implicated in cadmium metabolism and tolerance were also assessed to better understand differential NAGase responses: activity of glutathione S-transferases (GST), glutathione peroxidase (GPx) glutathione reductase (GR), levels of total glutathiones (TG), lipid peroxidation (LPO), lactate dehydrogenase (LDH), and NADP+-dependent isocitrate dehydrogenase (IDH). Animals from the moderately polluted estuary had lower NAGase activity both in the epidermis and digestive gland than in the low impacted site. NAGase activity in the epidermis and digestive gland of C. maenas from both estuaries was sensitive to cadmium exposure suggesting its usefulness for inclusion in monitoring programmes. However, in the digestive gland NAGase inhibition was found in crabs from the less impacted site but not in those from the moderately contaminated one. Altered glutathione levels were observed in cadmium-treated crabs from the contaminated site possibly conferring enhanced tolerance to these animals through its chelator action. Investigation of enhanced tolerance should thus be accounted for in monitoring programmes employing NAGase as biomarker to avoid data misinterpretation

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved