Germ-free sea bass Dicentrarchus labrax larval model: a valuable tool in the study of host-microbe interactions.

A thorough understanding of host-microbe interactions is crucial for more efficient disease management in the marine larviculture industry. As demonstrated in terrestrial animal research, gnotobiotic systems (involving animals cultured in germ-free conditions or inoculated with known microorganisms) are excellent tools to extend our understanding of the mechanisms involved in host-microbe interactions and allow the evaluation of new treatments for diseases. In this study, we introduce a germ-free European sea bass Dicentrarchus labrax larval model, independent of the continuous addition of antimicrobial agents. This model has an experimental set-up that allows addition of live feed to the larvae without compromising the germ-free status. This model will facilitate and render aquaculture research more effective in terms of mitigation fish larval diseases.

Flow cytometric bacterial cell counts challenge conventional heterotrophic plate counts for routine microbiological drinking water monitoring.

Drinking water utilities and researchers continue to rely on the century-old heterotrophic plate counts (HPC) method for routine assessment of general microbiological water quality. Bacterial cell counting with flow cytometry (FCM) is one of a number of alternative methods that challenge this status quo and provide an opportunity for improved water quality monitoring. After more than a decade of application in drinking water research, FCM methodology is optimised and established for routine application, supported by a considerable amount of data from multiple full-scale studies. Bacterial cell concentrations obtained by FCM enable quantification of the entire bacterial community instead of the minute fraction of cultivable bacteria detected with HPC (typically < 1% of all bacteria). FCM measurements are reproducible with relative standard deviations below 3% and can be available within 15 min of samples arriving in the laboratory. High throughput sample processing and complete automation are feasible and FCM analysis is arguably less expensive than HPC when measuring more than 15 water samples per day, depending on the laboratory and selected staining procedure(s). Moreover, many studies have shown FCM total (TCC) and intact (ICC) cell concentrations to be reliable and robust process variables, responsive to changes in the bacterial abundance and relevant for characterising and monitoring drinking water treatment and distribution systems. The purpose of this critical review is to initiate a constructive discussion on whether FCM could replace HPC in routine water quality monitoring. We argue that FCM provides a faster, more descriptive and more representative quantification of bacterial abundance in drinking water.

Role of transparent exopolymer particles on membrane fouling in a full-scale ultrafiltration plant: feed parameter analysis and membrane autopsy.

Ultrafiltration (UF) is widely used for water purification, but membrane fouling remains an important issue. In this study, the role of transparent exopolymer particles (TEPs), recently put forward as possible major foulants, was investigated in the fouling process of a full-scale UF installation. Algae, TEPs and other parameters in the UF feed were monitored and correlated during an 8 months long full-scale operation. Results revealed a complex fouling mechanism involving interactions mainly between algae, Fe (flocculant) and TEPs. Algae related parameters rather that TEP concentrations correlated stronger with irreversible fouling rates, suggesting that the overall role of TEPs in membrane fouling seems limited for this application. Finally, membrane autopsy showed the formation of a thick Fe-rich fouling layer on top of the fouled membranes, which could mostly be removed via cleaning-in-place. It remained partly irremovable in the form of some Fe-organic complexes.