Marine Microbes: a Hidden Smorgasbord of Nanoparticles

   Modern nanotechnology is being held back by the absence of sustainable and green methods of synthesising nanoparticles; current methods are burdened with the financial and environmental expense of using toxic materials; plus they use 'top down processes' which demand large amounts of wastage and energy. The best candidate alternative is the manipulation of organisms using biotechnological 'bottom up processes'; they have been tentatively practised across the domains of life from microbes to plants. Microbes are suitable for nanoparticle synthesis because many are adapted to heavy metal exposure, which they extensively use metabolic processes such as absorption, precipitation and chelation which form nanoparticle  byproducts. Since marine microbes are diverse across a range of unique marine niches such as high salinity, extreme pressure, low nutrients and high heavy metal concentrations, their potential for yielding novel nanoparticles is promising; but interest in marine microbes is only gathering now and this resource has yet to be utilised.

   Most non-marine microbes secrete cell wall proteins to form extracellular complexes with metal ions, creating nanoparticle precipitates, which clump together into crystals and must be broken apart to yield nanoparticles for human use. Marine microbes have a radically different way of dealing with metal ions; before intracellular storage, they attach phosphate/carbonate/sulfide groups to metals and sequester them with peptides such as glutathione. The advantage of this for us is that because marine microbe nanoparticles are bound to peptides, they will not crystallise into bulky aggregations, increasing nanoparticle stability.

   This review reports demonstrations of marine microbe nanoparticle synthesis; two marine actinomycetes produced silver nanoparticles and a range of different particle properties were possible by altering temperature and silver nitrate concentrations. Six marine fungi were also able to synthesis similar nanoparticles; additionally, it was confirmed that each particle was surrounded by a stabilising peptide. Cubic silver nanoparticles across a range of sizes could be produced by a marine Pseudomonas isolate and marine microalgae have been shown to be capable of making silver nanoparticles which are antimicrobial towards human pathogens. Antimicrobial activity of silver nanoparticles from the marine yeast Candida sp. and cyanobacteria have also been reported to work against multi drug resistant pathogens. But its not all just silver; the marine yeast Rhodosporidium diobovatum was able to synthesis cubic lead nanoparticles.

   As this field currently stands, it seems our seas contain a vast library of nanoparticles with different potential uses in medicine, industry and biotechnology is awaiting discovery. The strong motives for tapping into this resource may be a major driving force in advancing marine microbiology, furthering our understanding in areas such as how to culture what is currently unculturable and the extent of marine microbial diversity.

Baker, S., Harini, B. P., Rakshith, D., & Satish, S. (2013). Marine microbes: Invisible nanofactories. Journal of Pharmacy Research.