Sequentially aerated membrane biofilm reactors for autotrophic nitrogen removal: microbial community composition and dynamics

Membrane-aerated biofilm reactors performing autotrophic nitrogen removal can be successfully applied to treat concentrated nitrogen streams. However, their process performance is seriously hampered by the growth of nitrite oxidizing bacteria (NOB). In this work we document how sequential aeration can bring the rapid and long-term suppression of NOB and the onset of the activity of anaerobic ammonium oxidizing bacteria (AnAOB). Real-time quantitative polymerase chain reaction analyses confirmed that such shift in performance was mirrored by a change in population densities, with a very drastic reduction of the NOB Nitrospira and Nitrobacter and a 10-fold increase in AnAOB numbers. The study of biofilm sections with relevant 16S rRNA fluorescent probes revealed strongly stratified biofilm structures fostering aerobic ammonium oxidizing bacteria (AOB) in biofilm areas close to the membrane surface (rich in oxygen) and AnAOB in regions neighbouring the liquid phase. Both communities were separated by a transition region potentially populated by denitrifying heterotrophic bacteria. AOB and AnAOB bacterial groups were more abundant and diverse than NOB, and dominated by the r-strategists Nitrosomonas europaea and Ca. Brocadia anammoxidans, respectively. Taken together, the present work presents tools to better engineer, monitor and control the microbial communities that support robust, sustainable and efficient nitrogen removal

Diversitat bacteriana a les esponges marines

L’objectiu principal del projecte era aprofundir en el coneixement de les malalties de les esponges, centrant-nos en la diversitat bacteriana que acullen. Als estius 2008 i 2009 va haver episodis d’elevades temperatures de l’aigua de mar que van suposar importants mortalitats massives d’esponges a la Mediterrània. Contra tot pronòstic, els estius del projecte, el 2010 i el 2011, no van resultar especialment calorosos i no hi va haver episodis de mortalitat. És un fet molt positiu per les comunitats bentòniques però algun dels objectius específics de la meva proposta no es va poder dur a terme com havien estat platejats inicialment. Disposàvem de diferents mostres d’esponges malaltes de l’espècie Ircinia fasciculata, sanes i aigua circumdant recollides l’estiu 2009 i fixades per DNA, per això s’han pogut identificar i caracteritzar els canvis en la comunitat microbiològica de les esponges malaltes respecte de les sanes. Hem constatat que més que una infecció per un o pocs patògens puntuals, com havien proposat alguns autors, hi ha un canvi dràstic en la comunitat microbiològica associada a les esponges. Les esponges malaltes, on dominen els bacteris heterotròfics, presenten una major diversitat bacteriana que les sanes, on dominen els autòtrofs. Tot i que no es va poder realitzar un nou mostreig d’individus malalts, i algun objectiu específic no es va poder desenvolupar, vaig aprofitar l’estada en un centre de referència en estudis de la diversitat microbiana, per ampliar el coneixement general de les comunitats bacterianes associades a esponges. Es van realitzar nous estudis en què vam testar si totes les esponges (bacteriosponges i no) presenten simbionts reals o si les no-bacteriosponges presenten un enriquiment de les comunitats de l’aigua de mar però no una flora específica. El resultat és que totes les esponges presenten associacions molt específiques malgrat hi ha fortes diferències entre les comunitats microbianes associades a bacteriosponges i a no-bacteriosponges.

Spatial distribution and biomass of aquatic rooted macrophytes and their relevance in the metabolism of a Mediterranean coastal lagoon

This work aims to characterise the current autotrophic compartment of the Albufera des Grau coastal lagoon (Menorca, Balearic Islands) and to assess the relationship between the submerged macrophytes and the limnological parameters of the lagoon. During the study period the submerged vegetation was dominated by the macrophyte Ruppia cirrhosa, which formed dense extensive meadows covering 79% of the surface. Another macrophyte species, Potamogeton pectinatus, was also observed but only forming small stands near the rushing streams. Macroalgae were only occasionally observed. Macrophyte biomass showed a clear seasonal trend, with maximum values in July. The biomass of R. cirrhosa achieved 1760 g DW m-2, the highest biomass ever reported for this species in the literature. The seasonal production-decomposition cycle of the macrophyte meadows appears to drive the nutrient dynamics and carbon fluxes in the lagoon. Despite the significant biomass accumulation and the absence of a washout of nutrients and organic matter to the sea, the lagoon did not experience a dystrophic collapse. These results indicate that internal metabolism is more important than exchange processes in the lagoon.