A fascinating article appeared in a recently-published edition of Water Environmental Research detailing how cyanobacteria handle higher-than-normal concentrations of organic and inorganic mercury. The objective was to assess monomethylmercury toxicity to cyanobacteria by measuring growth rates, uptake and cell density, and to gauge the effectiveness of suspected EPSs, or extracellular polymeric substances: protein complexes in the cyanobacterium’s cell wall that quarantined toxic mercury on the outside of the cell.
Their results were, in some ways, unsurprising. Cell density declined notably as mercury concentrations increased, and EPS concentration rose, confirming their suspicions that it did indeed play a role. But what is most interesting is the uptake of mercury into the cells:
For lower doses of mercury, uptake remained roughly the same, albeit increasing slightly. But what is interesting is that high doses of mercury result in significantly higher levels of mercury uptake, implying that there is a critical point at which any countermeasures to prevent uptake become ineffective. Or, perhaps it simply implies that the EPSs work both ways, locking in whatever mercury is uptaken.
It would be interesting to see if similar countermeasures exist for other organisms. Active removal is one thing, but direct prevention of uptake is quite another. Perhaps this could prove useful for dealing with heavy metal pollution. Maybe strains of cyanobacteria could be produced with EPSs that could be switched on and off, allowing them to freely and rapidly uptake mercury from the environment and then lock it away.
Chen, Ho-Wen, Wo, You-Xuan, Huang, Winn-Jung. 2014. Methylmercury accumulation and toxicity to cyanobacteria: implications of extracellular polymeric substances and growth properties. Water Environment Research 86(7):626-634.