Bioavailability, bioaccumulation and tolerance of chromium: consequences in the food chain of freshwater ecosystems

Many abiotic and biotic factors can influence the partitioning equilibrium of heavy metals, thus influencing metal impact on aquatic environments. Unicellular algal species release soluble organic substances able to complex metals. In our laboratory a Cr-tolerant strain was selected and isolated from a wild type strain of Scenedesmus acutus. The exudates released by the two strains counteracted the growth inhibition caused by Cr(VI) and the exudates of the Cr-tolerant strain were more effective. On the contrary, the exudates did not reduce chromium toxicity to the cladoceran Daphnia magna. The reduction of chromium effect on algae seems the consequence of an algae-specific interaction among Cr(VI), exudates and algal cells. Chromium uptake resulted to be energy-dependent since bioaccumulation rate in subdued light condition was lower than at high light intensity. The effect of Cr(VI) on algae changed depending on metabolism of the cells and in particular it seemed to be related to the bioaccumulation rate. Tolerance in the selected strain could not be ascribed to a lower uptake of chromium. The difference in sensitivity to chromium between the two strains was exploited to evaluate if tolerance acquired by algae could have consequences for Daphnia. After treatment with Cr(VI), the two strains of S. acutus were used as food source for D. magna. The results indicate that chromium is accumulated by algae in a form not available for daphnids and that Cr tolerance acquired by the algae can be of some advantage to the consumer organism.     

The natural and synthetic indole weaponry against bacteria

The emergence of drug resistant bacterial infections leading to high mortality rates has posed a formidable challenge to organic synthesis and medicinal chemists to deliver potent and novel antibacterial drug candidates. In particular, antibacterial agents based on novel chemotypes and first-in-class drug candidates with novel mode of actions are highly desired. Indole scaffold has found a consistent presence in the bioactive molecules of synthetic and natural origin. The potential of indole based small molecules as antibacterial agents has not been as much explored as in other areas of medicine, like cancer therapy. In this review, we present a brief account of indole based antibacterial small molecules which have been either synthesized in the laboratory or isolated from natural sources and provide intriguing potential leads in the antibiotic drug discovery research.