Non-human microbiomes


This post drew on elements of my own Honours project, which I undertook in 2008. Yes, it’s been awhile, but I still love science. I hope this is interesting to someone. Please feel free to comment.

Microbiomes seem to be the talk of the town at the moment. This microbial underworld is intrinsically linked to many aspects of life we take for granted. It’s actually a lot more inextricably linked than most of us know or suspect. Studies of mammalian subjects have shown that microbiota are crucial. In fact, axenic mammals fare very poorly in comparison to their microbe infested kin.

I have posted a series of links to articles via my social media about not only the physiological importance of having a microbiota,  but also about how intimately entwined these hitchhikers have become with complex life-including us.

Aphids harbour a bacteria called Buchneria wolbachia…

Shown here residing within bacteriocytes; modified fat cells in the host aphid’s hindgut

At this point in time a great deal of research has been carried out on human microbiota: gastrointestinal,  mouth etc. Of invertebrates, sponges have been the object of most study. 

Sponges have been around for nearly 800 million years, and stand testament to an old adage: if it ain’t broke, don’t fix it.

Big Pharma has taken to the seas in recent years, upon realising it is a treasure trove of bio-active compounds which may be of use in combating disease,  including cancer.
Molluscs have been an increasing avenue of research as the neverending war between modern humanity and disease rages on. A predatory marine whelk; Dicathais orbita has been one such focus of research. This snail produces bio-active compounds believed to have anti-cancer properties.

One interesting aspect of this emphasis on invertebrates as a source of new medicines is that it highlights a possible role for bacteria in production of these compounds. For example, molluscs such as D. orbita are the only molluscs to employ a class of compounds called bromoperoxidases in the production of bio-active compounds. However, gene sequencing of D. orbita has turned up no genes or proteins that synthesise these compounds. Subsequent searches of databases such as NCBI has turned up nearly a hundred bacterial genes for bromoperoxidases. 

Microbiomes (in the case of D. orbita) do exist. Whereas they have been exhaustively catalogued in humans only recently have studies into invertebrates and their structures begun to bear fruit. 

In D. orbita, bacteria show selective colonisation of differing regions within the snail. Certain organs and glands are known to be bio-active; for example rectal and hypobranchial glands. These regions show low diversity of bacterial passengers. In contrast non biosynthetic centres; gut, mantle and foot showed a seemingly random and diverse spread of bacteria. This is easily explained by environmental uptake.

A female specimen of D.orbita. Highlighted (white arrow) are two biosynthetic centres: the hypobranchial gland and rectal gland, both of which show a structured bacterial complement.

This seemingly selective dispersal of differing bacterial spp. suggests mechanisms by which certain bacterial groups favour particular locations within organisms. Once they have taken a hold there they then proceed to earn their keep; in the case of D. orbita providing chemical defences against other bacteria and pathogens. 
Bacteria are supreme opportunists, having been found almost in literally every environment on and under earth. Whereas they have a natural tendency to form semi-structured, semi-organised communities known as biofilms they also just as readily colonise other organisms, co-opting them for shelter and other benefits whilst paying their way. Their role in the rise and continued existence of. multicellular life can not be overstated.

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