Production of methyl mercury in the gut of the Australian termite Mastotermes darwiniensis

Abstract

Animals are often exposed to or can ingest heavy metals along with their food. Therefore, we tested whether the hindgut microbiota of Mastotermes darwiniensis possesses the capability to form methyl mercury. The termite M. darwiniensis (Isoptera) was fed with saw dust containing different concentrations of inorganic mercury. Methyl mercury was determined by purge‐and‐trap capillary gas chromatography‐atom fluorescence spectrometry (CGC‐AFS) using ethyl mercury chloride as the internal standard. Total mercury concentrations were determined in the termite tissue by inductive coupled plasma‐isotope dilution mass spectrometry (ICP‐IDMS) after microwave‐assisted digestion. The obtained results showed in vivo methyl mercury production in terrestrial insects for the first time. Desulfovibrio intestinalis isolated from M. darwiniensis was identified as a biomethylating species of the intestinal microbiota.

Methylation of Mercury in Earthworms and the Effect of Mercury on the Associated Bacterial Communities

“…Limper et al [35] tested the ability of termites ( Mastotermes darwinesis ) to methylate inorganic-Hg. They found an in vivo methylation of Hg in termites and identified SRB ( Desulfovibrio intestinalis ) in their intestinal tract as important players in the formation of methyl-Hg.…”

Mercury-methylating bacteria are associated with copepods: A proof-of-principle survey in the Baltic Sea

“…Notably, the morphology of cladoceran gut predisposes it to active oxygenation, and gut microbiota in these animals is dominated by clones affiliated to aerobic or facultative anaerobic bacteria [38], which may explain the lack of hgcA amplification in our cladoceran samples. Hg-methylating genes have been detected in invertebrate microbiota, including termites, beetles, and oligochaetes [5,16], and in some invertebrates the endogenous MeHg production has been documented [39]. As a life form, intestinal microbiota exists in biofilms, and such communities are increasingly recognized as important sites for environmental Hg methylation [40,41].…”

Is gastrointestinal microbiota relevant for endogenous mercury methylation in terrestrial animals?

“…However, there was some contradictory results related to Desulfovibrio intestinalis 11275. These had been found as methylators by Limper et al (2008), but no activity was found by Kaschak et al (2014). The different initial IHg concentration (one hundred times lower in the latter study) could be a possible reason.…”

“…In vivo study using Desulfovibrio intestinalis isolated from the gut of termite M. darwiniensis fed with saw dust of spruce containing different concentrations of IHg Limper et al (2008) Isopod (Porcellio scaber) In vivo study using isopod P. scaber fed with 203 Hg 2 þ or CH 3 203 Hg þ dosed food Jereb et al (2003) In vivo study with isopod P. scaber fed with hazelnut leaves spiked with 203 Hg 2 þ Nolde et al (2005) Earthworms…”

“…Nevertheless, it is likely that the conditions favourable for SRB could enable methylation and, for that reason, the presence of SRB could be considered as a good starting point to identify potential Hg methylation in invertebrates. Limper et al (2008) tested the Australian termite Masotermes darwiniensis (Isoptera) because the presence of SRB in its intestine is known (Dröge et al, 2005;Fröhlich et al, 1999) and they could be a good model organism. The termites were fed with saw dust containing different concentrations of spiked IHg (25-250 mg/g) for 14 days and then the total Hg and MeHg were analysed in the whole specimen.…”