Hiking With A Field Microscope
Copyright © 2004, Wayne Lanier, PhD
A Hard Life Out in the Salt Flats
TABLE OF CONTENTS
Secrets of a San Francisco Deck Garden
Giant Bacteria Found in Golden Gate Park Flowers...!
Cryptobiotic Soil Unearthed in Utah
Revealing Films of Life in a Cliff-side Seep
A Hard Life Out in the Salt Flats
Beneath the Tufas in Mono Lake
The south end of San Francisco Bay has provided salt to man
for at least a thousand years. When the Spaniards came they found
a thriving evaporative salt production on the salt flats. At the
height of salt production, during the mid-twentiety century, giant
salterns produced tons of salt.
The aerial photograph below, taken by Cris Benton, shows part of the Don Edwards where he and I hiked with field microscopes. Water in the large saltern, part of the former salt works, showed 24.4-percent salt. The red color of the saltern is the result of tiny motile algae called "dinoflagelates" living in the water.
Between the saltern and the slough is a salt marsh dense with pickleweed. Many small ponds dot the salt marsh. We sampled one at about the position of the pointer extending out from the words "Salt Marsh" in the photograph above. Water in the salt marsh pond was 5-percent salt, still higher than the Bay water salt content.
We found two distinct communities in the pond we sampled and we observed similar comunities in the other ponds. Representatives from the two communities are shown below.
One community, shown on the right, was defined by masses of green algae; the other, shown on the left, by masses of red bacteria.
Some of these communities were tiny, some were quite large - covering as much area as a square meter. Often a red bacteria colony would be only a few centimeters from a green colony, with the colonies almost touching. Measurements did not show differences in water temperature, pH, or salinity between a green algal colony and a red bacterial colony. Examination of the microbial populations in each commuity, however, showed substantial differences.
First, the red bacteria... A photomicrograph from the red colony sample is shown below:
At 100X magnification, the large red colonies turned out to be dominated by many fluffy red microcolonies. Here the microcolonies are lit from the side to show their appearance. They are so dense that the larger microcolonies are opaque. It took close examination of the smaller microcolonies to show they consist of masses of small bacteria. This is shown in the next photomicrograph.
The "granular" structure of the microcolonies becomes apparent
at 400X. The bacteria that make up these microcolonies are
probably purple non-sulfur bacteria, a general term for a group of
photosynthetic bacteria exhibiting a red color because of carotenoid
pigment. Non-sulfur bacteria may be cocci, rods, or
spirals. Some produce gelatinous substances, as may be the
situation here where a gel probably binds these microcolonies
together.
These colonies were often surrounded by large motile bacterial
rods,
as can be seen by playing a brief movie by clicking here. You need a
QuickTime player to play the movie. To return to this page, use
the <Back> button on your browser.
The large motile rods are probably not part of the red
bacteria colony,
but may be attracted to the colony by its metabolic products.
Colony bacteria appear to be much smaller and granular in appearance,
as
shown below.
The large communities of red bacteria did not remain as discrete colonies throughout the year. In the winter, when rain and increased run-off from streams disturbed the slough and its ponds, the neat colonies were smeared along the edges of the ponds.
Many other microorganisms were associated with the red
bacterial colony community. Some of these other microorganisms
were also found in the green algae community, but most are unique to
the
red bacterial colony community. These included diatoms,
dinoflagelates, cyanobacteria, other kinds of bacteria, and
protozoa. For example, here is a "spiral" or "vibrio" bacterium,
shown at 800x magnification. These bacteria were fast, tumbling
along with a spiral motion.
You can see the spiral motion of these bacteria if you click here. Use your
<Back> button to return to this page.
In the the red bacterial colony community we found many
dinoflagelates:
Click here for a
movie of one of these dinoflagelates. After viewing it, return to
this page by using your <Back> button.
Among the dinoflagelates were ciliate protozoa.
The ciliate protozoa is on the left of the image, a
microcolony of red bacteria is at the bottom. Click here for a movie showing several
of the ciliates playing among the red bacteria and cyanobacteria.
Use your <Back> button to return to this page.
Can you guess what the ciliate shown below has been eating?
The photozynthetic red bacteria are at the bottom of the food
chain, the ciliates are just a little higher up. Shown below are
two ciliates conjugating. In the protozoa, conjugation is a way
of exchanging genetic material.
Click here to see a movie of
these conjugating ciliates. If you view the movie, you can see
that conjugation does not impair their mobility. Use the
<Back> button to return to this page.
Below, a large cyanobacterial filament is in a sheath.
These cyanobacteria were slowly motile. They are also
photosynthetic, so are at the bottom end of the food chain.
Click here to see a movie
of cyanobacteria and ciliates.
Some of the cyanobacteria were red in color, although they
were clearly not like the red bacteria. The cause of the red
color was not apparent. These may have been a different species
of cyanobacteria, normally red pigmented... Or they may have been
the same cyanobacteria that were normally green, but had become red for
some reason.
The red-bacteria community also had many diatoms. Shown
below are two commonly found:
Click here to see a movie of
this diatom. Use your <Back> button to return. Below
is another common diatom.
Although this has been only a brief survey of the red-bacteria
community, it is now time to examine the green-algae community next
door.
To be continued...