Interesting post by Samantha Andrews on bioluminescence in parchment worms.

Interesting post by Samantha Andrews on bioluminescence in parchment worms. 

Originally shared by Samantha Andrews

If you go down to the beach and take a look and the sand after the tide has receded, chances are you will see lots of holes.  Chances are, these holes belong to one of a number of different marine worm species which burrow into the sand.  These guys tend not to be visible until the tide comes back in and covers them over…or you go digging them up. There are a lot of species of marine worms spanning a multitude of different phyla.  Marine worms have been found in pretty much every type of marine habitat we have explored.  This is a hugely diverse group but today we are going to take a look at just one of these intriguing little critters – Chaetopterus species, or more commonly known as the parchment worms.

The parchment worm is a member of what we call polychaetes – segmented worms belonging to the phyla annelida.  Parchment worms are found pretty much everywhere….from shallow waters down to hundreds of meters deep.  No matter where these worms lay their hat, their home is always constructed in the same way.  The parchment worm secretes mucus from its body, which hardens into cylinders around it.  You may have seen the tops of these cylinders that stick out of the burrows – they (allegedly) look a little bit like parchment paper (see where they got their name from!).  But that’s not the only trick mucus trick this worm has.  It is known to emit bioluminescent ‘puffs’ of blue light…particularly when poked by divers.  There are a lot of unanswered questions about this bioluminescent mucus.  We know that the bioluminescent properties comes from a photoproetin, but why have a blue bioluminescent mucus at all.  Most critters that use bioluminescence in shallow water environments emit green light not blue, because the green wavelength travels farthest in this depth of water (blue light is better for the deep sea).  Dimitri Deheyn and his colleagues at Scripps and Georgetown University  in the USA were intrigued so they set out to see if they could start to unravel some of the properties of this unexpected blue light.

The team started out by collecting the worms from the La Jolla submarine canyon, just off San Diego, California…around 20 – 30m down and kept in aquariums.  The works were then dissected (they used something called hypothermal anaesthesia – placing them on ice – to ‘put them to sleep’) and then sections of the worms were treated with potassium chloride to stimulation mucus secretion.  A whole host of measurements and recordings were then done on the mucus, which was exposed to different temperatures and different oxygen levels, and a few other bits and pieces.  

It seems that no matter which part of the body the researchers collected mucus from, bioluminescent properties were found, but there were some surprising differences.  The mucus in the anterior (near its head) contains less protein than the other part of the body, yet its mucus produced a rather “intense and long-lasting light”.  The researchers weren’t able to confirm one way or another if the compounds that produce this light come from the same ones that are used to construct those tubes for these critters to live in, but they were able to uncover some interesting things about the properties of this intriguing mucus.  Denser mucus produces less light than when the mucus was diluted with seawater, which may be why we don’t see the tubes ‘glow’ blue, but we can see the puffs in the water.  They also found that these little critters were able to produce this blue light even in anoxic conditions (where there is no oxygen), but adding hydrogen peroxide could damped the light produced.  Apparently that last point is very unusual and not what the researchers were expecting to see at all.  Most critters that are luminous produce light when they find themselves faced with hydrogen peroxide so what’s going on here?  Well The researchers suspect that the hydrogen peroxide influences the mucus itself, rather than the phytoprotein that produces the light.  

It also became apparent that not all of the worms produced equal amounts of mucus.  There were also differences in its viscosity, and how intense the light produced was.  Why this is the case is yet to be fully resolved but the researchers highlight a number of factors that may impact on the mucus.  This includes factors like the size or sex of the worm, the time of year the worms were collected from the field, or even their diet.  Actually this last point about diet seems to have been backed up by another study Dimitri was involved in.  In that study, the work showed that riboflavin was vital for the light produced in the mucus, but the worms can’t generate that riboflavin themselves.  Where do they get it from?  Probably their diet, but the possibility of a symbiotic relationship with a bacteria that produces riboflavin hasn’t been discounted yet.  

The paper is published in the journal Physiological and Biochemical Zoology – you can find an open access copy of it here http://ow.ly/qSM2v

Image:  Full-body imaging of live Chaetopterus sp. marine worm in bright field (left) and fluorescence (right), with indication of the studied body parts. H, head; MA, middle anterior; MP, middle posterior; T, tail.  Taken from the paper by Deheyn et al. (2013)

#marinescience   #sciencesunday   #biology   #bioluminescence   #marineworms