The complexity of porphyrin-like pigments in a marine annelid sheds new light on haem metabolism in aquatic invertebrates

Abstract

True green pigments in the animal kingdom are scarce and are almost invariably porphyrinoids. Endogenous porphyrins resulting from the breakdown of haem are usually known as “bile pigments”. The pigmentation of intertidal Polychaeta has long gained attention due to its variety and vivid patterning that often seems incompatible with camouflage, as it occurs with Eulalia viridis, one of the few truly green Polychaeta. The present study combined UV and bright-field microscopy with HPLC to address the presence and distribution of pigments in several organs. The results showed two major types of porphyrin-like pigments, yellowish and greenish in colour, that are chiefly stored as intraplasmatic granules. Whereas the proboscis holds yellow pigments, the skin harbours both types in highly specialised cells. In their turn, oocytes and intestine have mostly green pigments. Despite some inter-individual variation, the pigments tend to be stable after prolonged storage at −20 °C, which has important implications for future studies. The results show that, in a foraging predator of the intertidal where melanins are circumscribed to lining the nervous system, porphyrinoid pigments have a key role in protection against UV light, in sensing and even as chemical defence against foulants and predators, which represents a remarkable adaptive feature.

Light-Mediated Toxicity of Porphyrin-Like Pigments from a Marine Polychaeta

“…In accordance with our previous findings (Martins et al [ 20 ]), the extracts from the “greenish” skin and the “yellowish” proboscis of Eulalia viridis contain multiple pigments and sustain very significant inter-organ variation. However, the extraction methods were distinct between the two works, albeit HPLC-DAD being used for fractioning in either case.…”

“…Whereas we previously used HCl:acetonitrile to extract the pigments, in the present work we opted for extraction in PBS to obtain a physiologically compatible vehicle for the bioassays. The most notorious difference is the higher representativity of individual yellowish pigments in the skin found in the current work relatively to Martins et al [ 20 ]. Nonetheless, the main pigments, in particular the yellow compound retrieved at retention time 4.40 min ( Figure 3 D and Figure 5 D) is seemingly present in the extracts from our preceding work.…”

“…It must also be noticed that the extracts from the skin caused DNA damage and suggest a potential dose-response and light-mediated toxicity as well. However, as pointed out in our previous work, this organ holds a much wider variety of pigments than the proboscis [ 20 ], which complicates, at this stage, isolating specific substances of interest and obtaining sufficient amounts for analyses.…”

“…Recently, we showed that an uncanny uniformly green Polychaeta, Eulalia viridis , an opportunistic predator of the rocky intertidal, owes its coloration to a multiplicity of endogenous porphyrin-like pigments whose abundance and distribution changes between organs [ 17 , 18 , 19 , 20 ]. These pigments, which seem to almost entirely replace common biochromes such as carotenoids and melanins, were found to be chiefly stored as granules allocated within unique specialized chromocytes [ 19 , 20 ]. The function and bio-reactivity of these pigments is not, however, fully understood.…”

Chemical evidence of rare porphyrins in purple shells of Crassostrea gigas oyster

“…The discovery of a rare and natural source of porphyrins offers here an unprecedented opportunity to give more added value to purple waste oyster shells. Although extraction yield and purification still need to be improved, the extraction of porphyrins may have significant potentials for biotechnology or photoactivation applications 49,50 .…”