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This study identified the most common epiphytes infecting the algal host Gracilaria chilensis on a farm in northern Chile. Simultaneously, the types of host-epiphyte interfaces were characterized and their relative abundance and temporal variability were monitored. Five types of anatomical relationships were detected. Infection type I included the epiphytes weakly attached to the surface of the host and not associated with damage of host tissues (i.e. Hincksia mitchelliae, H. granulosa and Ectocarpus acutus). Infection type II included those epiphytes strongly attached to the surface of the host but not associated with any host tissue damage (i.e. Acrochaetium sp., Antithamnionella sp. and Colpomenia sinuosa). Infection type III included all the epiphytes that penetrated the outer layer of the host wall without damaging its cortical cells (i.e. Xenococcus sp. and Sahlingia subintegra). Infection type IV included epiphytes penetrating deep into the host cell wall, disorganizing the cortical tissue (i.e. Ulva lactuca and Acrosorium corallinarum). Infection type V included epiphytes that penetrated deeply into the cortex, reached the medullary tissue and caused destruction of the host's cells in the area around the infection (i.e. Ceramium rubrum and Polysiphonia harveyi). Prevalence varied with time and with infection type, with types II and III reaching up to 80% and 90% of the thalli respectively. Severity of epiphyte infection was similar to the distribution of infection prevalence, with crustose epiphytes colonizing up to 80% of the host surface.

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The two agar-producing red algae, Gracilaria chilensis C. J. Bird, McLachlan & E. C. Oliveira and Gracilaria conferta (Schousboe ex Montagne) Montagne, responded with hydrogen peroxide (H 2 O 2 ) release when agar oligosaccharides were added to the medium. In G. conferta, a transient release was observed, followed by a refractory state of 6 h. This response was sensitive to chemical inhibitors of NADPH oxidase, protein kinases, protein phosphatases, and calcium translocation in the cell, whereas it was insensitive to inhibitors of metalloenzymes. Transmission electron microscopic observations of the H 2 O 2 -dependent formation of cerium peroxide from cerium chloride indicated oxygen activation at the plasma membrane of G. conferta. A putative system, consisting of a receptor specific to agar oligosaccharides and a plasma membranelocated NADPH oxidase, appears to be responsible for the release of H 2 O 2 in G. conferta. Subcellular examination of G. chilensis showed that the H 2 O 2 release was located in the cell wall. It was sensitive to inhibitors of metalloenzymes and flavoenzymes, and no refractory state was observed. The release was correlated with accumulation of an aldehyde in the algal medium, suggesting that an agar oligosaccharide oxidase is present in the apoplast of G. chilensis. The presence of this enzyme could also be demonstrated by polyacrylamide electrophoresis under nondenaturating conditions and proven to be variable. Cultivation of G. chilensis at 16 to 171 C resulted in significantly stronger expression of agar oligosaccharide oxidase than cultivation at 121 C, which indicates that the enzyme is used under conditions that generally favor microbial agar macerating activity.Specific cell wall-derived oligosaccharides are known to regulate growth, development, and defense responses in higher plants (Darvill et al. 1992, Aldington and Fry 1993, John et al. 1997, Braam 1999, Vorwerk et al. 2004. Examples of recognition of oligosaccharides have also been reported for marine algae. Agar oligosaccharides released from the cell wall matrix of Gracilaria conferta (Schousboe ex Montagne) Montagne control the abundance of agar degrading bacteria at the surface of this alga (Weinberger and Friedlander 2000). Similarly, alginate oligosaccharides from the cell wall matrix of kelp sporophytes play a key role during the induction of resistance against algal endophytes and bacteria in the brown algae Laminaria digitata and Macrocystis pyrifera, respectively (Küpper et al. 2002). 1

Since the fatty acid ester profile of a given biofuel is relatively consistent with the source's fatty acid profile, the properties of the biodiesel produced from a particular feedstock exhibit predictable quality. Thus, lipid fractions and the fatty acid composition of stationary growth-phase cultures of the local strains of the diatoms Skeletonema costatum and Navicula gregaria were analysed to evaluate their suitability as biodiesel feedstock. Total lipid content was 20.83 pg cell −1 in S. costatum and 19.17 pg cell −1 in N. gregaria. Neutral lipids were the main fraction of total lipids in both species, accounting for ca. 65% and 76%, respectively. S. costatum was predominant in saturated fatty acids (SFAs; 43.48 %) and monounsaturated fatty acids (MUFAs; 40.11%), while N. gregaria was predominant in MUFAs (54.85%), followed by SFAs (33.42%). In S. costatum, the main fatty acids in neutral lipid fraction were myristic, palmitic, palmitoleic and oleic acids, while the main ones in N. gregaria were palmitic and palmitoleic acids. The oils extracted from these species presented linolenic acid contents within biodiesel's quality specifications. However, in neutral lipid fraction both species showed eicosapentaenoic acid levels higher than the required limit. The lipid quality analysed in both species suggests that a biodiesel derived from these oils may present an acceptable cetane number, but likely poor coldflow properties. This baseline information is useful for future research tending to find more suitable conditions in order to improve oil yield. In addition, both estuarine species neither compete with agriculture for food nor require farmland nor fresh water.

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