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Thursday, 12 February 2015

Mud, glorious mud

By Jacqueline Campbell


Connections are often established in the most unexpected manner. How many times do you come away from a situation thinking “it’s a small world”, where just the opportune mention of a single word or phrase strikes a chord and is enough to foster new links and an avenue by which to share new ideas.

As unlikely as it seems, the words “pond mud” brought the Red Maids’ School together with the University of Bristol Botanic Garden recently. And from this link, students at the school have gone on to create their own miniature sustainable ecosystems using mud gathered from the garden’s mature and established ponds.

Marvellous muddy mesocosms

Mrs Turner, Head of Biology at Red Maids' School, studying
the mesocosms.
Sixth Form students following the International Baccalaureate biology curriculum are required to complete a number of practical experiments. One of these is the creation of a mesocosm known as a Winogradsky column; essentially a self-contained, sustainable ecosystem grown in a sealed plastic bottle under controlled conditions.

A critical element of this experiment is pond mud. As they are situated no more than a couple of miles apart, the Red Maids’ School approached staff at the Botanic Garden for their advice and assistance in setting up such an ecosystem.  A number of phone calls and a few visits later, two groups of students have used pond mud sourced from the Botanic Garden and are watching to see the bacteria in their stratified ecosystems develop. 

The mesocosms in this image are just a few hours old.
Images are taken every two days to track and record the changes
over time.
The mesocoms now live on a sunny window sill in the Biology Department at Red Maids’, and are a constant source of curiosity to all. Despite a little reluctance mainly associated with the smell of pond mud, the students involved are thrilled to have created their own ecosystems and are often now found enthusing about the colour of their bacteria and amount of respiration they can see.

Images taken every two days are providing a good record of how the ecosystems are developing over time. From an initial cloudy but uniform situation, clearly defined layers are forming coupled with a notable increase in the pressure within the bottles showing the incredible amount of respiration that is occurring within the system.

Bacteria of many colours

Students have seen the pressure within their ecosystems
increase over time thanks to the highly visible levels of
respiration occurring within the sealed environment. A range
of different coloured bacteria are also now present.
The ingredients required to create the Winogradsky column are: pond mud, shredded newspaper, crushed egg shells and raw egg yolk. Pond mud provides a suitable base while the newspaper, egg shell and egg yolk provide sources of carbon, carbon dioxide and sulphur respectively. As a first step, these components are mixed together and poured into the bottom of a plastic fizzy drinks bottle.

On top of this layer comes another of compost, followed finally by some pond water. The idea is that many different coloured layers of bacteria develop, and each of these transforms molecules for the others to use. And as long as there is light entering the system, the column should theoretically continue to maintain a healthy microbial ecosystem for many months.

Waiting to develop: Over time, students at Red Maids' hope
to see their Winogradsky columns develop into a stratified
system. This will provide a visual example of various modes of
metabolism and zonation in the microbial world. The
mesocosm shown in this image is several months old. 
Conditions at the bottom of the column are highly anaerobic with a high sulphide concentration ideal for the growth of sulphate reducing bacteria, green sulphur bacteria and purple sulphur bacteria. Moving higher in the column, with conditions becoming more aerobic and a reduction in sulphide concentration, we can expect to see the development of purple non-sulphur bacteria, iron-oxidizing bacteria, heterotrophic bacteria and cyanobacteria. 

Of course none of this would be possible without the kind assistance of the Botanic Garden staff, who waded into freezing winter waters to collect the mud. The Red Maids’ School is very grateful to have established this connection, and hopes that it too will blossom over time. 

Dr Jacqueline Campbell has a PhD in physics from St Andrews University and twelve years of editorial experience working for the Institute of Physics Publishing and as a freelance journalist. She now works as a science technician at the Red Maids' School.