|PhytoMarsh - The phytosphere of salt-marsh plants: an underexplored microbial hot-spot|
Programme - PTDC/AAC-AMB/118873/2010
Execution dates - 2012-04-02 - 2015-09-30 (42 Months)
Funding Entity - FCT
Funding for CESAM - 160000 €
Total Funding - 160000 €
Proponent Institution - Universidade de Aveiro
It is the overall aim of this project to perform a detailed characterisation of the microbial communities associated with salt marsh plants in Ria de Aveiro, most specifically those plants living in mercury contaminated sites and that are able to tolerate and accumulate this toxic metal. For this we will apply culture-dependent as well as culture-independent molecular approaches to unravel the bacterial diversity within these phytosphere communities, at the below ground level (rhizosphere), the aerial portion (phyllosphere) and also inside the plant tissues (endophytic bacteria).
In the last years there has been a growing interest in the use of plants to remediate environments (phytoremediation) polluted with a variety of contaminants, namely metals. In fact, because salt marsh plants are adapted to the salt marsh environment they are regarded as perfect candidates for phytoremediation of contaminated salt marshes. It is known that metal phytoextraction can be influenced by microorganisms living in intimate association with plants by increasing the tolerance of the plant to metals, or by behaving as plant growth promoting bacteria (PGPB). With the aim of identifying strains that are potential candidates to be used in microbial-assisted phytoremediation of salt marshes, we will characterise isolates obtained in this study concerning a set of traits that are generally regarded as having a plant growth promoting effect.
Human pathogens have been found in the phytosphere (phyllosphere and rhizosphere) of diverse plants including salt marsh plants which raises considerable concern regarding environmental safety and human health. Considering that multiple antibiotic resistances have been found in strains isolated from the phytosphere and that metal-resistance and antibiotic resistance determinants are commonly co-selected, there is even more reasons for concern as multiple resistant bacteria may enter the food chain. In the case of Ria de Aveiro salt marshes, this can be a serious danger since the contaminated sites are in the vicinity of areas highly exploited in terms of fishery and bivalve capture. Therefore, we will additionally characterise the phytosphere microbial communities regarding two important aspects, namely the occurrence of resistances and resistance genes and simultaneously the presence of mobile genetic elements (MGEs). This characterisation will be performed not only by culture-based methods but also by culture-independent methods in order to assess relevant information that may be contained in those members of the community that cannot be retrieved in isolation plates. Metal and antibiotic resistances are often associated with mobile genetic elements. The association of such genetic traits with mobile genetic elements, like plasmids, transposons and integrons contribute for their wide dispersion in the environment. Phytosphere (including the rhizosphere and phyllosphere) has already been shown to harbor a diversity of MGEs and exhibit high rates of horizontal gene transfer. With this project we aim to understand if the phytosphere of salt marsh plants represents a hot-spot for the evolution and dissemination of resistance genes and the risk it may represent to the environment and humans.