Energy status and immune system alterations in Elliptio complanata after ingestion of cyanobacteria Anabaena flos-aquae

Cyanobacteria have often been described as nutritionally poor for herbivorous organisms. To gain additional information on the potential impacts of invertebrates feeding on cyanobacteria, we fed Elliptio complanata mussels with two types of algae: Anabaena flos-aquae (cyanobacteria) and Pseudokirchneriella subcapitata (green algae). Physiological parameters were examined at the energy status, immune system and oxidative stress levels. Energy status was examined by following the rate of electron transport activity in mitochondria (a measure of cellular energy expense) and lipid/sugar stores in the visceral mass. The cyanobacteria were not actively producing toxins. Based on the digestive gland index, the mussels fed equally on either regime. However, the energy status in mussels fed A. flos-aquae revealed that the total sugar was lower in the digestive gland, whereas mitochondrial electron transport activity (MET), once corrected against the digestive gland somatic index, showed increased energy expenses. Acetylcholinesterase activity and lipid peroxidation (LPO) were also higher in mussels fed with A. flos-aquae compared with mussels fed with P. subcapitata. LPO was correlated by mitochondrial activity in both the digestive gland and gills, suggesting that oxidative stress resulted from metabolic respiration. Immunocompetence (phagocytic activity, natural killer cell-like activity, haemocyte count and viability) and humoral level of lysozyme were not affected in mussels by the algae or cyanobacteria regime. Moreover, the xenobiotic conjugating enzyme, glutathione S-transferase, hemoprotein oxidase and vitellogenin-like proteins were not affected in mussel organs via ingestion of A. flos-aquae. Our study suggests that ingestion of cyanobacteria leads to increased energy expenses, oxidative stress and increased acetylcholine turnover in mussels.

Actin-related proteins in Anabaena spp. and Escherichia coli

Actin has been described in all eukaryotic cells as the major microfilament cytoskeletal protein. Although prokaryotic cells do not have a cytoskeleton, proteins related to the latter have been found in different prokaryotic species. We have found prokaryotic actin-related proteins in the enterobacterium Escherichia coli and in the cyanobacteria Anabaena cylindrica and Anabaena variabilis. They were identified by the following criteria: (1) by cross-reaction with a fluorescent conjugated anti-actin (rat-brain) mAb by Western blot analysis (in total cellular extracts); (2) specific binding of acetone powder and soluble cellular extracts to DNase I; and (3) specific binding of cells and total cellular extracts to phalloidin. In E coli, specific binding of phalloidin labelled with rhodamine to cells was detected by spectrofluorometry. In total cellular extracts, three bands of 60, 43 and 35 kDa were weakly recognized by the mAb by Western blot analysis; this recognition increased when phalloidin was added to the extracts. Furthermore, three polypeptides of kDa were isolated by binding to DNase I, showing pI values of 6.7, 6.65 and 6.6, less acidic than all reported actin pI values. In A. cylindrica and A. variabilis, specific binding of phalloidin labelled with rhodamine to cells was also detected by spectrofluorometry. In total and soluble cellular extracts, the mAb recognized two bands of 45 and 40 kDa by Western blot analysis, but only the first was purified by binding to DNase I, and it showed three isoforms of pI values 6.8, 6.5 and 6.4. These results suggest the presence, in prokaryotes, of proteins with similar biochemical characteristics to eukaryotic actin.

Antibodies to the N-terminal sequence of GVPa bind to the ends of gas vesicles

Antibodies were raised against intact gas vesicles of Anabaena flos-aquae, and against a synthetic peptide (GVPaNT) whose sequence is identical to the N-terminal region of the main gas vesicle protein, GVPa. A two-stage centrifugation procedure is described for separating gold-labelled antibodies bound to gas vesicles from unbound antibodies. The GVPaNT antibody bound to gas vesicles that had been previously rinsed with SDS to remove the outer gas vesicle protein, GVPc. Treatment with this antibody caused the gas vesicles to aggregate together end-to-end rather than side-by-side. The binding of the anti-GVPaNT-immunogold particles to the gas vesicle was restricted to the conical ends of the structure. These observations indicate that the sequence to which the GVPaNT antibodies were raised, residues 1 to 13 of the GVPa molecule, is exposed only at the outer surface of the cones and that it is normally obscured by GVPc. As GVPa forms both the conical ends and the cylindrical midsection of the gas vesicle, exposure of the N-terminal sequence only in the cones must be due to differences in the contact between adjacent GVPa molecules in the central cylinders and end-cones.