Marine-derived fungus as biosynthesizer of silver nanoparticles

Nano materials are of interest in a broad range of applications in various fields such as mechanics and biomedical sciences. The synthesis of nanoparticles with more diverse properties is of increasing interest; however it is somewhat limited due to the costs and the hazard of toxic chemicals involved. Novel and safer methods are therefore required, and recently marine microbial cells have been identified as potential sources for the synthesis of nanoparticles. Among these, marine-derived fungi in the Gulf of Khambhat have been found as promising metal nanoparticle producers, since many fungal species from this area have been previously recognised as efficient metal removers. 

The potential as silver nanoparticle (AgNP) synthesiser of the marine fungus Aspergillus flavus was analysed in this study which was isolated from the West Coast of India. After culturing, the fungus was added to different concentrations of AgNO_3. An effect was observed after 24 h of incubation; change in the colouration of the mixtures indicated intracellular synthesis of AgNPs from AgNO₃, and colouration and thus biomass of AgNPs increased with time. However, from spectrophotometric measurements it was suggested that a certain concentration is needed to detect significant amounts of AgNPs. 

Additionally, the effects of different pH to the biosynthesis activity of A. flavus were examined, and results revealed that more alkaline pH had significant impacts on the synthesis of AgNPs. At pH ranges from 3-7, intracellular biosynthesis occurred, whereas from pH 8 to 10, extracellular synthesis was concluded (indicated by different colouration) and higher pH generally showed faster changes of the solutions than more acidic ones. 

To summarise, the results from this study showed that the marine fungus A. flavus has the ability to synthesise AgNPs intracellularly from AgNO₃. Moreover, alkaline pH increased the extracellular biosynthesis of these nano particles. The authors pointed out that this species is a potential candidate for an environmentally friendly producer of the economically important metal nanoparticles. However, with the increasing ocean acidification I can see a limitation of such applications in the field (e.g. in the with metals heavily polluted Gulf of Khambhat from ship yeards) but rather under laboratory controlled conditions. Undoubtedly, the utilisation of A. flavus for the production of AgNPs would be very beneficial, especially when the use of harmful chemicals could be avoided. Ideally, the waters could be “cleaned” of metals with the introduction of similar species and NPs exploited at the same time. Yet is unclear how this would affect the ecosystem in general, so precaution would be required. An interesting study nonetheless with potential for future uses.

Vala et al. (2014). Biogenesis of Silvernanoparticles by Marine-Derived Fungus Aspergillus flavus from Bhavnagar Coast, Gulf of Khambhat, India. J Mar Biol Oceanogr 3:1.