Money doesn’t grow on trees… (2) [Or, From cuddly koalas to bird poo…]

Could the koala's diet of eucalyptus result in gold?
Image: David Iliff/Wikimedia Commons (CC-BY-SA 3.0).
Image: David Iliff/Wikimedia Commons (CC-BY-SA 3.0).

OK, I know, this item is the real ‘money doesn’t grow on trees’ story you were expecting. So, I’ll try not to disappoint. Melvyn Lintern et al. provide the first evidence of particulate gold (Au) within natural – i.e. not from laboratory experimentation (and therefore which evidence doesn’t count..?) – specimens of living biological tissue.  The living biological tissue in question is that of the iconic Australian plant species eucalyptus, the gum tree. Apparently, and hitherto, reports of Au from plant samples have led to questions as to whether the Au was within the tissues (and therefore absorbed) or adsorbed onto the external surfaces as a result of aerial contamination. The team consider their discovery to demonstrate active biogeochemical absorption of Au, and it may therefore be used as a sort of bioassay (quite how quantitative this is may require further testing – maybe even experimentation…) to indicate the presence of soil-based Au deposits within the reach of the tree’s roots (the presumed route for uptake of the metal from the soil). The overall effect of this study is a little spoilt by the final sentence of the abstract, which begins, ‘This observation conclusively demonstrates active biogeochemical adsorption of Au…’. Shouldn’t that ante-penultimate word be absorption? Potential use of plants as agents to absorb metals – and other compounds – from soils and waters has been widely touted as a method for cleaning up such environments and comes under the broad category of phytoremediation. However, the fact that some plants may accumulate economically important metals – such as gold – has long been recognised and underlies the practice of geobotanical prospecting, which apparently dates as far back as the 5th century BCE in China. Whilst this study isn’t necessarily proposing use of eucalyptus in a bioindicator capacity, the authors do suggest that the gold therein might be extractable on a commercial basis. For more on this topic, see Sheoran et al.’s articles on ‘phytomining’ in general and of that for gold in particular. Anyway, I think somebody’s missing a trick here. What’s the iconic Australian animal species? The herbivorous koala, which famously has a diet rich in leaves of… eucalyptus. Now, applying the well-known principle of biomagnification – whereby organisms higher up the food chain accumulate materials from what they feed on – if koalas can be persuaded to eat only Au-loaded gum-tree leaves, then maybe their faecal pellets may contain gold, but concentrated to much higher levels than those found within their food source. Just a little nugget (!) of information I’m happy to share. All somebody needs to do is harvest the stuff (but isn’t that why postgrads/postdocs were invented..?). What’s that you say, where there’s muck there’s brass? Indeed! After all, we all know how expensive coffee is when made from the ‘beans’ that have been peristaltically massaged and ‘processed’ by passage through the alimentary tract of the Asian palm civet! And in a more scientifically imaginative  – though similarly scatologically-inclined – ‘muck = brass’ way the veracity in this wise saying is verified by work in Australia’s antipodean neighbour, New Zealand. Exhibit A, the evidence base that is the coprolite (‘fossilized feces’)  recently exploited by Jamie Wood et al. [http://dx.doi.org/10.1073/pnas.1307700110] to discern information about the ecology of four sympatric (species living in the same geographical area) species of moa – flightless herbivorous birds, which became extinct in New Zealand about 600 years ago. Unfortunately, there’s insufficient space for the details of the study here, but it involves identification of vegetation from pollen, aDNA (ancient DNA),  and plant macrofossils within the bird droppings (and therefore inferences about moas’ diet and habitat). This is a great example of that admirable ‘rolling-up-your-shirt-sleeves-and-getting-your-hands-dirty’ dedication to the cause of true science; definitely not merely going through the motions(!). What, after all, is more valuable than brass, or even gold? Knowledge! Well, some sorts of knowledge anyway, because, and rather vaguely, the Antipodean team’s ‘golden gum tree’ article just mentions ‘Eucalyptus trees’; there’s no further taxonomic help to their identity in the Supplementary Information either. So, although the article itself is Open Access, maybe naming the species concerned is too commercially sensitive for general consumption?