Genome analysis of the freshwater planktonic Vulcanococcus limneticus sp. nov. reveals horizontal transfer of nitrogenase operon and alternative pathways of nitrogen utilization

Background: Many cyanobacteria are capable of fixing atmospheric nitrogen, playing a crucial role in biogeochemical cycling. Little is known about freshwater unicellular cyanobacteria Synechococcus spp. at the genomic level, despite being recognised of considerable ecological importance in aquatic ecosystems. So far, it has not been shown whether these unicellular picocyanobacteria have the potential for nitrogen fixation. Here, we present the draft-genome of the new pink-pigmented Synechococcus-like strain Vulcanococcus limneticus. sp. nov., isolated from the volcanic Lake Albano (Central Italy). Results: The novel species Vulcanococcus limneticus sp. nov. falls inside the sub-cluster 5.2, close to the estuarine/marine strains in a maximum-likelihood phylogenetic tree generated with 259 marker genes with representatives from marine, brackish, euryhaline and freshwater habitats. V. limneticus sp. nov. possesses a complete nitrogenase and nif operon. In an experimental setup under nitrogen limiting and non-limiting conditions, growth was observed in both cases. However, the nitrogenase genes (nifHDK) were not transcribed, i.e., V. limneticus sp. nov. did not fix nitrogen, but instead degraded the phycobilisomes to produce sufficient amounts of ammonia. Moreover, the strain encoded many other pathways to incorporate ammonia, nitrate and sulphate, which are energetically less expensive for the cell than fixing nitrogen. The association of the nif operon to a genomic island, the relatively high amount of mobile genetic elements (52 transposases) and the lower observed GC content of V. limneticus sp. nov. nif operon (60.54%) compared to the average of the strain (68.35%) support the theory that this planktonic strain may have obtained, at some point of its evolution, the nif operon by horizontal gene transfer (HGT) from a filamentous or heterocystous cyanobacterium. Conclusions: In this study, we describe the novel species Vulcanococcus limneticus sp. nov., which possesses a complete nif operon for nitrogen fixation. The finding that in our experimental conditions V. limneticus sp. nov. did not express the nifHDK genes led us to reconsider the actual ecological meaning of these accessory genes located in genomic island that have possibly been acquired via HGT

A sombra do arquitecto, da colaboração entre João Andresen e Teófilo Rego

Do levantamento do espólio do fotógrafo Teófilo Rego podemos concluir que dos vários profissionais da “Escola do Porto” com quem colaborou intensivamente entre as décadas de 1940 e 1960, a figura que mais se destaca é sem dúvida a do arquitecto João Andresen (1920/67). Como nenhum outro, o lote das imagens da obra deste autor revela de facto, pela quantidade e diversidade do material fotográfico, uma colaboração regular, sem igual, que abrange um número considerável dos seus trabalhos, desde o projecto que apresenta ao concurso para o Monumento ao Infante D. Henrique (1954/56) ao Plano de Desenvolvimento Turístico dos Reis Magos na ilha da Madeira (1964). A comunicação passa em revista as diversas reportagens que Rego realizou das obras e projectos de Andresen, aborda as histórias, as razões e os motivos que estão na sua origem, demonstrando como desde cedo a fotografia constituiu para os profissionais portugueses um instrumento imprescindível tanto na elaboração de arquivos de memória pessoal como na divulgação e apresentação dos seus trabalhos em concursos, exposições e revistas, ou ainda como meio de comunicação e suporte das ideias que pretendiam afirmar.Este texto foi co-financiado pela Fundação para a Ciência e a Tecnologia I.P. (PIDDAC) e pelo Fundo Europeu de Desenvolvimento Regional – FEDER, através do COMPETE – Programa Operacional Fatores de Competitividade (POFC), no âmbito do projecto "Fotografia, Arquitectura Moderna e a «Escola do Porto»: Interpretações em torno do Arquivo Teófilo Rego" (PTDC/ATP-AQI/4805/2012

Photosynthetic and growth response of freshwater picocyanobacteria are strain-specific and sensitive to photoacclimation

We investigated the effect of different light conditions on primary production and growth rates of three closely related freshwater picocyanobacterial strains from three different ribotypes in laboratory cultures. The primary goal was to test whether not only different pigment types (PC-rich versus PE-rich) but also other physiological characteristics suggested by different phylogenetic positions could affect growth and photosynthetic rates of picocyanobacteria. Secondly, we tested whether photacclimation is strain specific. Experiments were conducted over light intensities ranging from 6 to 1500 μmol photons m−2 s−1 with cultures that were acclimated to low (10 μmol photons m−2 s−1) and moderate (100 μmol photons m−2 s−1) irradiance. The PE-rich strain was sensitive to high light conditions and reached highest photosynthesis and growth rates at low light intensities. The relative effect of photoacclimation was different between the two PC-rich strains, with one strain showing only moderate changes in growth rates in response to the light level used during the acclimation period. Overall, growth rates differed widely in response to light intensity and photoacclimation. Photoacclimation significantly affected both primary production and growth rates of all three strains investigated. We conclude that strain-specific photoacclimation adds to the niche partitioning among closely related freshwater picocyanobacteria

Colorful Niches of Phytoplankton Shaped by the Spatial Connectivity in a Large River Ecosystem: A Riverscape Perspective

Large rivers represent a significant component of inland waters and are considered sentinels and integrators of terrestrial and atmospheric processes. They represent hotspots for the transport and processing of organic and inorganic material from the surrounding landscape, which ultimately impacts the bio-optical properties and food webs of the rivers. In large rivers, hydraulic connectivity operates as a major forcing variable to structure the functioning of the riverscape, and–despite increasing interest in large-river studies–riverscape structural properties, such as the underwater spectral regime, and their impact on autotrophic ecological processes remain poorly studied. Here we used the St. Lawrence River to identify the mechanisms structuring the underwater spectral environment and their consequences on pico- and nanophytoplankton communities, which are good biological tracers of environmental changes. Our results, obtained from a 450 km sampling transect, demonstrate that tributaries exert a profound impact on the receiving river’s photosynthetic potential. This occurs mainly through injection of chromophoric dissolved organic matter (CDOM) and non-algal material (tripton). CDOM and tripton in the water column selectively absorbed wavelengths in a gradient from blue to red, and the resulting underwater light climate was in turn a strong driver of the phytoplankton community structure (prokaryote/eukaryote relative and absolute abundances) at scales of many kilometers from the tributary confluence. Our results conclusively demonstrate the proximal impact of watershed properties on underwater spectral composition in a highly dynamic river environment characterized by unique structuring properties such as high directional connectivity, numerous sources and forms of carbon, and a rapidly varying hydrodynamic regime. We surmise that the underwater spectral composition represents a key integrating and structural property of large, heterogeneous river ecosystems and a promising tool to study autotrophic functional properties. It confirms the usefulness of using the riverscape approach to study large-river ecosystems and initiate comparison along latitudinal gradients