Role of bacterivorous organisms on fungal-based systems for natural tannin degradation.

Tannery wastewater presents high concentrations of organic load and pollutant recalcitrant molecules (e.g. tannins), which reduce the efficiency of biological treatment processes. Recent studies showed that several fungal species and strains are effective in the degradation of tannins. However, high bacterial load can negatively affect fungal growth, reducing system stability and degradation performances. The aim of the present study was to evaluate the effects of the introduction of bacterivorous grazers (ciliates and/or rotifers) in batch scale experiments using fungi to remove Tara tannin, i.e. to check the potential synergistic effect between fungi and bacterivorous grazers in the degradation of recalcitrant compounds. In this context, the ciliated grazers Paramecium calkinsi, Tetrahymena sp., Pseudovorticella sp., and the rotifer Lecane inermis, preliminary selected according to their ability to grow in a solution prepared with Tara tannin, were separately tested. Activated sludge, including a complex mixture of native grazers, was used as experimental control. The following parameters were monitored: bacterial load, number of grazers/mL and Soluble Chemical Oxygen Demand (SCOD). Colony Forming Unit (CFU)/grazers ratio was also calculated. Particular attention was paid to: i) bacterial load reduction and ii) enhancement of recalcitrant compounds degradation, and we observed that in all experimental conditions where grazers occurred bacterial load was significantly reduced and the system achieved a higher SCOD removal in a shorter time. Our findings provide useful insights for the stabilization of fungal-based systems in non-sterile conditions.

High degree of specificity in the association between symbiotic betaproteobacteria and the host Euplotes (Ciliophora, Euplotia).

The Betaproteobacteria-Euplotes association is an obligatory symbiotic system involving a monophyletic group of ciliate species and two betaproteobacteria species which can be alternatively present. Recent data showed that this relationship has been established more than once and that several symbiont-substitution events took place, revealing a complex and intriguing evolutionary path. Due to the different evolutionary pathways followed by the different symbionts, each bacterial strain could have differentially evolved and/or lost functional traits. Therefore, we performed re-infection experiments, both by phagocytosis and by microinjection, to test the possible functional role of the different bacteria towards the ciliates. Our results confirm that the growth capacity of the host is indissolubly linked to the presence of its original symbionts. Results of the attempts of re-infection by phagocytosis showed that none of the bacteria is able to successfully colonize the host cytoplasm in this way, even if regularly ingested. Re-infection by microinjection succeed only in one case. Such results point to a high degree of specificity in the interactions between bacteria and Euplotes even after the invasion step. Due to a co-evolutive pathway of reciprocal adaptation, different degree of re-colonization ability could have been conserved by the different species and strains of the symbionts.