Taking Root: Enduring Effect of Rhizosphere Bacterial Colonization in Mangroves

Mangrove forests are of global ecological and economic importance, but are also one of the world's most threatened ecosystems. Here we present a case study examining the influence of the rhizosphere on the structural composition and diversity of mangrove bacterial communities and the implications for mangrove reforestation approaches using nursery-raised plants.A barcoded pyrosequencing approach was used to assess bacterial diversity in the rhizosphere of plants in a nursery setting, nursery-raised transplants and native (non-transplanted) plants in the same mangrove habitat. In addition to this, we also assessed bacterial composition in the bulk sediment in order to ascertain if the roots of mangrove plants affect sediment bacterial composition. We found that mangrove roots appear to influence bacterial abundance and composition in the rhizosphere. Due to the sheer abundance of roots in mangrove habitat, such an effect can have an important impact on the maintenance of bacterial guilds involved in nutrient cycling and other key ecosystem functions. Surprisingly, we also noted a marked impact of initial nursery conditions on the rhizosphere bacterial composition of replanted mangrove trees. This result is intriguing because mangroves are periodically inundated with seawater and represent a highly dynamic environment compared to the more controlled nursery environment.In as far as microbial diversity and composition influences plant growth and health, this study indicates that nursery conditions and early microbial colonization patterns of the replants are key factors that should be considered during reforestation projects. In addition to this, our results provide information on the role of the mangrove rhizosphere as a habitat for bacteria from estuarine sediments

Assessment of variation in bacterial composition among microhabitats in a mangrove environment using DGGE fingerprints and barcoded pyrosequencing

Here, we use DGGE fingerprinting and barcoded pyrosequencing data, at six cut-off levels (85-100%), of all bacteria, Alphaproteobacteria and Betaproteobacteria to assess composition in the rhizosphere of nursery plants and nursery-raised transplants, native plants and bulk sediment in a mangrove habitat. When comparing compositional data based on DGGE fingerprinting and barcoded pyrosequencing at different cut-off levels, all revealed highly significant differences in composition among microhabitats. Procrustes superimposition revealed that ordination results using cut-off levels from 85-100% and DGGE fingerprint data were highly congruent with the standard 97% cut-off level. The various approaches revealed a primary gradient in composition from nursery to mangrove samples. The affinity between the nursery and transplants was greatest when using Betaproteobacteria followed by Alphaproteobacteria data. There was a distinct secondary gradient in composition from transplants to bulk sediment with native plants intermediate, which was most prevalent using all bacteria at intermediate cut-off levels (92-97%). Our results show that PCR-DGGE provides a robust and cost effective exploratory approach and is effective in distinguishing among a priori defined groups.This study was funded by the Deutsche Forschungsgemeinschaft SM59/4-1 and 4-2 (www.dfg.de/en/index.jsp), FAPERJ-Brazil (www.faperj.br), Centre for Environmental and Marine Studies (CESAM, Portugal) (www.cesam.ua.pt), Foundation for Science and Technology (FCT, Portugal) PTDC/AAC-CLI/107916/2008 (http://alfa.fct.mctes.pt) and the European Regional Development Fund (ERDF) through COMPETE- (FCOMP-01-0124-FEDER-008657). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.publishe

LEVEDURA COMO UM EXEMPLO DE DIVERSIDADE MICROBIANA EM ECOSSISTEMAS BRASILEIROS

The high degree of biodiversity among microorganisms is noted and some of the problems involved in studies of microbial communities are presented using yeasts as an example. Considerable data are available on yeasts of temperate regions and substantial collections of yeasts from these studies exist, but studies of yeasts in tropical environments have been rare and mostly focused on medical applications. The diversity and distribution of yeasts in animals, aquatic and terrestrial environments including sand dune (restinga) ecosystems, Drosophila of rain forests, and fruits in Brazil are reviewed. These studies have shown different habitats to have characteristic yeast communities often including many new biotypes and probable new species.A presente revisão trata da biodiversidade microbiana nos diversos ecossistemas enfatizando os problemas envolvidos no estudo das comunidades de leveduras como exemplo desse tipo de estudo. Existe uma quantidade considerável de dados na literatura sobre as leveduras como exemplo desse tipo de estudo. Existem uma quantidade considerável de dados na literatura sobre as leveduras nas regiões temperadas resultando na obtenção de muitas estirpes mantidas em coleções. Em contraste nas regiões tropicais poucos estudos foram efetuados, e a maioria dos trabalhos focaliza leveduras de interesse médico. Os estudos de diversidade e distribuição de leveduras em ambientes aquáticos e terrestres incluindo ecossistema de restinga, Drosophila de florestas, frutos e animais feitos no País foram discutidos. Esses estudos indicam que habitats diferentes possuem comunidades de leveduras características, revelando muitos biótipos diferentes que provavelmente representam novas espécies

Results of adonis analyses with the Bray-Curtis distance matrix of OTU composition as the response variable and microhabitat the independent variable.

<p>Results of adonis analyses with the Bray-Curtis distance matrix of OTU composition as the response variable and microhabitat the independent variable.</p

Ordination showing the first two PCO axes of the <i>Betaproteobacteria</i> only analysis for a) 85% cut-off level with 97%, b) 91% cut-off level with 97%, c) 92% cut-off level with 97%, d) 95% cut-off level with 97%, e) 100% cut-off level and f) DGEE data with 97% cut-off level.

<p>The arrows in the ordination point to the target configuration, the actual symbols represent the rotated configuration, i.e., the ordination based on the 97% cut-off values. Correlation (Corr) and significance values are given in the lower right corner of each graph.</p

Diversity of ndo Genes in Mangrove Sediments Exposed to Different Sources of Polycyclic Aromatic Hydrocarbon Pollution▿

Polycyclic aromatic hydrocarbon (PAH) pollutants originating from oil spills and wood and fuel combustion are pollutants which are among the major threats to mangrove ecosystems. In this study, the composition and relative abundance in the sediment bacterial communities of naphthalene dioxygenase (ndo) genes which are important for bacterial adaptation to environmental PAH contamination were investigated. Three urban mangrove sites which had characteristic compositions and levels of PAH compounds in the sediments were selected. The diversity and relative abundance of ndo genes in total community DNA were assessed by a newly developed ndo denaturing gradient gel electrophoresis (DGGE) approach and by PCR amplification with primers targeting ndo genes with subsequent Southern blot hybridization analyses. Bacterial populations inhabiting sediments of urban mangroves under the impact of different sources of PAH contamination harbor distinct ndo genotypes. Sequencing of cloned ndo amplicons comigrating with dominant DGGE bands revealed new ndo genotypes. PCR-Southern blot analysis and ndo DGGE showed that the frequently studied nah and phn genotypes were not detected as dominant ndo types in the mangrove sediments. However, ndo genotypes related to nagAc-like genes were detected, but only in oil-contaminated mangrove sediments. The long-term impact of PAH contamination, together with the specific environmental conditions at each site, may have affected the abundance and diversity of ndo genes in sediments of urban mangroves

Assessing variation in bacterial composition between the rhizospheres of two mangrove tree species

This study aimed to determine to what extent roots from the common mangrove tree species Avicennia schaueriana and Laguncularia racemosa are able to impose a selective force on the composition of sediment bacterial communities in mangrove intertidal sediments using barcoded pyrosequencing analysis of 16S rRNA gene fragments (V4 hyper-variable region). The novel results showed that root systems of A.schaueriana and L.racemosa are associated with increased bacterial dominance, lower richness and compositional shifts of sediment bacterial communities. The proportion of OTUs (operational taxonomc units) belonging to the orders Rhizobiales and Vibrionales were enriched in rhizosphere samples from both plant species and sulphur-reducing bacteria (SRB) belonging to the order Desulfobacterales and Desulfuromonadales were enriched in the rhizosphere of A.schaueriana. In addition, Clostridium and Vibrio populations were more abundant in different mangrove rhizospheres. A.schaueriana and L.racemosa roots appear to be able to impose a selective force on the composition of mangrove sediment bacterial communities and this phenomenon appears to be plant species specific. Our findings provide new insights into the potential ecological roles of bacterial guilds in plant-microbe interactions and may aid rhizoengineering approaches for replanting impacted mangrove areas