Ma del Pilar Gracia

Determination of organic loading rate of activated sludge plants based on protozoan analysis

Abstract Variations in the structure of the protozoan community living in activated sludge were studied in relation with the organic loading rate. 84 samples were taken over a 14 month period. Sludge and wastewaters were subjected to microscopic and physico-chemical analyses. The organic loading rate corresponding to each microscopic count was determined as the average of the values calculated for the 2 days previous to the count. Ciliate species abundance and specific diversity of ciliates were strongly related to the organic loading rate. Data were compared to three other facilities. Ciliate diversity decreased as the organic loading rate increased. This relationship could be modified if solids in suspension surpassed 4000 MLVSS mg/l or if volumetric loading rates were higher than 800 g BOD 5 /m 3 day. An easy, fast diagnostic test to estimate the organic loading rate in less than 5 days and to obtain information on plant performance is proposed.

FORAMINIFERAL COLONIZATION ON ARTIFICIAL SEAGRASS LEAVES

Colonization of seagrass leaves was studied using artificial ribbon-like substrates. The study was carried out in a seagrass ( Posidonia oceanica (L.) Delile) meadow off the Medes Islands (NW Mediterranean). Artificial leaves of different colors and textures were immersed at two depths (5 and 13 m), and retrieved after 3 and 6 months; epiphytic foraminifera were identified and counted, and the results were compared with those obtained from natural leaves. Although some differences were found in the colonization of the various types of artificial leaf (e.g., smooth, green leaves with float bladder had the highest number of individuals and species) ANOVA and cluster analyses revealed that the type of substrate did not significantly affect the colonization by foraminifera; the main sources of variability were mainly seasonality and, to a minor extent, water depth. Thus, the dominant species were the same in both natural and artificial leaves. The calcareous perforated shells and the trochospiral morphotype were the most abundant, and the dominant biological types were groups B and C, i.e., temporarily or permanently mobile species.

Longevity and effects of temperature on the viability and polar-tube extrusion of spores of Glugea stephani, a microsporidian parasite of commercial flatfish.

Abstract Food contamination with respect to microsporidiosis in humans (associated with acquired immunodeficiency syndrome) and in marine fish farming deserves particular attention. For the first time, a study on the longevity and resistance to both heat and freezing of the spores of a vertebrate microsporidian, Glugea stephani, parasitizing a commercial flatfish was carried out. As judged on the basis of determinations of the extrusion rate, the resistance of the spores to temperature stress was remarkable. The extrusion rate, which can be directly related to infectivity, was always lower than the viability (membrane integrity). It should be pointed out that neither heat (60° C for 30 min) nor freezing (−19° C for 24 h) caused a complete reduction in the extrusion rate or viability. Consequently, the ingestion of poorly cooked or raw fish (even if previously frozen) represents a danger for aquaculture and, probably, for immunodepressed patients.

Ciliated Protozoan communities in a fluvial ecosystem

The ciliated protozoan communities in the Llobregat River (Barcelona, Spain) were studied for one year. Samples were taken from 11 different stations. The physical-chemical factors of the water as well as the qualitative and quantitative nature of the ciliate populations were considered. 105 species of ciliates, grouped in 13 orders, were found.The species which constantly appeared at all 11 stations (although not every month) were Litonotus fasciola, Trithigmostoma cucullulus, Cyclidium glaucoma, Glaucoma scintillans, Vorticella microstoma, Oxytricha sp., Stylonychia mytilus, Aspidisca costata and Aspidisca lynceus. The index of diversity at the different stations, and the affinity between the most abundant species, were also determined.

The pathologic cycle of the infection of the microsporidian Microgemma ovoidea (Thèl., 1895) Amigó et al. 1996 in the liver of the Red Band fish (Cepola macrophthalma L.).

Abstract Pathologic study of the lesions caused by Microgemma ovoidea has shown that after the formation of the xenoma (stage 1), the parasitized cell is infiltrated by host macrophages (stage 2) and quickly encysted by the activity of fibroblasts that form a xenoma wall composed of collagenous fibers (stage 3). The phagocytic activity of the macrophages leads to the formation of a granuloma (stage 4) in which the cyst contents comprise macrophages filled with phagocytosed spores. This phagocytic activity is limited by the fact that some parts of the microsporidian spores, such as the spore walls, cannot be lysed by macrophages, which leads to the formation of fused giant cells containing nondigestible spore remnants. The final step in the process is healing (stage 5), in which some cells may start proliferating to regenerate the damaged area. Nevertheless, the host occasionally fails to control M. ovoidea infections. This failure can take two forms: bursting of the granuloma, or the appearance of secondary infections in granulomas, probably through parasitism of macrophages.