paper and an egg
can grow colonies of multi-hued microbes!
the 1880's, a Russian microbiologist named Sergei Winogradsky discovered
that water mud poured into a tall bottle and placed in the sun turned
many different colors. He found that by adding a few simple things,
such as sheese or paper, he could control which colors appeared.
Here's a recipe for making your own Winogradsky column.
clear tennis-ball container or plastic soda bottle with the
top cut off
top or plastic wrap and a rubber band
from a bay shore of the edge of a shallow pond (the smellier
newspaper page shredded
raw egg (without shell)
with a 40-watt incandescent bulb
do and to notice:
Remove any rocks or sticks from the mud, and put the mud in the
bowl. Mix it with water until it's the consistency of heavy cream.
the label from you container. Put in the shredded paper and egg,
add an inch of mud, and mix well. Then, fill the container with
mud up to an inch from the top and cover it. Wash your hands after
you complete the setup.
container about a foot from a 40-watt bulb that you can leave on
all the time. Every few days, briefly remove the container's top
to vent off the gases (if too much gas is allowed to build up, it
can blow the top off). If the mud at the top is drying out, add
a little water. In a few weeks, you'll see auras of brilliantly
colored bacteria. Keep watching, and you'll see the colors develop
and change during the next several months.
kinds of bacteria live in mud. Some are decomposers that get nutrients
by breaking down organic materials things like the egg and paper.
During the process of decomposition, all the oxygen near the bottom
of the container is used up.
bacteria are photosynthetic. Blue-green bacteria near the top of
the mud column use light, carbon from carbon dioxide, and hydrogen
from water to make carbohydrates and give off oxygen just like
plants. The carbon dioxide they need is released when the decomposers
break down the paper and egg.
orange and green bacteria that grow near the bottom of the column
are less tolerant or completely intolerant of oxygen. They're
photosynthetic, but they get their hydrogen from hydrogen sulfide,
the gas that smells like rotten eggs. In your container, hydrogen
sulfide is released when the decomposers break down the protein
in the egg.
mud contained some of each of these kinds of bacteria when you collected
it. You provided the bacteria with conditions that are just right
for them, and their populations exploded. The colorful patches are
colonies of billions of bacteria.
first billion years that life existed on the planet, the atmosphere
contained little oxygen. Bacteria like those at the bottom of your
mud column thrived. It wasn't until about two billion years ago
that the blue-green bacteria filled the atmosphere with its photosynthetic
waste product oxygen. This effectively banished other kinds of
bacteria to places where there is no oxygen to mud and sediments
and (more recently) to the insides of plants and animals.
oxygen-phobic bacteria still have crucial roles to play. Some take
part in the global sulfur cycle. Others convert nitrogen into forms
needed by plants. And neither cows nor termites would enjoy their
cellulose-based diets without the helpful bacteria in their guts
that digest the cellulose for them.