by SM Morgan
I recently helped an office mate clean out his Tenebrio culture, which had been infected and overrun with fungus. My scientific career to date has been primarily concerned with Mesorhizobium and Drosophila, so playing around with new ‘lab rats’ is a treat.
Tenebrio molitor in its larval form is commonly called ‘mealworm’ due to it having a predilection for infesting cereal silos. The larvae are also a favorite of pet shops, and are used to feed reptiles, fish and birds. It is occasionally common to raise them with added juvenile hormone which keeps them in the larval form and induces much larger growth. They are also used as fishing bait – the worm on the end of your hook. And, apparently, when baked or fried the larvae are touted as a ‘healthy snack food’. Delightful.
T. molitor is a holometabolous insect, which means it goes through complete body changes throughout its lifecycle. Starting as an egg, a larvae (maggot) hatches and feeds, molting as it grows, until big enough to pupate. The pupal form is mostly stationary while the body is reformed, and eventually hatches into the adult insect. A lovely video of a developing and hatching pupa can be seen here. The adult form of T. molitoris a beautiful Darkling beetle:
T. molitor adult. Photo: SM Morgan
And the larval and pupal forms have some undeniable cute-factor going on:
T. molitor is used in science for, as a quick sampling; determining protein structures, testing pesticides, environmental stress research (effects of temperature, radiation and toxins on the beetle; and its response), and even investigation into the larvae as an alternative food source for humans.
And in a quick segue, because this is fascinating – that last paper was investigating the use of the mealworm as a ‘bioregenerative life support system’ – for long term space habitation. Brilliant. Astronauts need animal protein, and if the worms can live off plant wastes – so much the better.
However, perhaps most interesting (due to my own exposure via office-mates), the larvae produce a protein commonly called an ‘antifreeze’ which slows the formation of ice crystals, prevents damage from these sharp water-shards and ensures the insect can survive colder temperatures – in this case down to -13 degrees Celsius. Antifreezes are typically called as such due to their ability to reduce the freezing temperature of a liquid, and can be salts, alcohols or proteins. For this reason, the scientific field studying this particular topic prefers the full term ‘antifreeze proteins’, to avoid confusion.
The applications of such additives go further than your car engine in winter – two brands of ice cream in the US contain antifreeze protein to avoid that horrible icing situation which you find in the 6 month-old container you had forgotten about in the deep freeze. Potential applications also include use in human organ/tissue transplant; if we could super-cool the organs without damaging the tissues by freezing, we could keep them in storage for longer, and potentially save more lives. Also, if we could improve the freeze-tolerance of crop plants, the growth and harvest seasons could be extended, providing more food for a starving world.
The antifreeze protein in T. molitor has been investigated in the laboratory traditionally via recombinant means. That is, the gene sequence for the protein is put into bacteria and the bacteria manufactures plenty of the protein of which you can then study. However, bacteria perform different post-translational modifications on their proteins than insects do – they do not cut (where T. molitor does), differently fold and manipulate their gene products after they have been made so that the protein you extract from bacteria is different to that which you extract from the beetle itself, even if the protein was made from the exact same gene sequence.
It has been suggested that these bacterial modifications alter the activity of the antifreeze protein, so James McKellar, a Master of Science student under the supervision of Dr Craig Marshall here at Otago, is investigating these differences between the bacterial-produced T. molitor antifreeze protein and the protein extracted directly from the beetle larvae itself. A process which involves instant death for many larvae via liquid nitrogen submersion.
The larvae are grown in porridge oats and while they can survive off metabolic water, an added piece of apple or carrot keeps them happy. However, if left too long or without adequate ventilation, the extra moisture from the fruit can start keeping other things happy – like a delightful green mould. Cleaning out the cultures involves tedious sifting of mouldy oats and built-up beetle waste, and picking out of beetles, pupa and larvae to place into clean, mould-free porridge. The larvae however, hatch from eggs too small to see without aid, and as such when young are very small; so the process becomes similar to panning for gold. The more help, the better.
Thus my playing about with a different insect for a short while.