Photo by Christine Fenton
Under phase contrast (X1000) we see the typical crescent shaped body
(1), the stalk (2), and rosette formation (3).
What's so Special?
Caulobacter are stalked aquatic
bacteria that are scavengers in nature. They are able to
survive during periods of nutrient exhaustion when all other bacteria
have died. They are also unusual because cell division results in two
different cell types, a stalked cell and a swarmer cell. The stalked
cell is a mature cell which immediately starts replicating its
chromosome in preparation for the next cell division. However, the
motile swarmer cell is an immature cell which is incapable of DNA
replication. In order to divide, it must differentiate by losing its
flagellum and synthesising a stalk in its place. The resulting stalked
cell then initiates DNA replication.
These non-pathogenic stalked cells appear
to have a role in the spread of antibiotic resistance genes. Strains
isolated from sewage had increased resistance to some antibiotics such
as chloramphenicol, tetracycline, erythromycin, and tobomycin. Some of
these antibiotics are in common clinical use, others are 'second
generation' antibiotics. These resistances may be due to plasmid
transfer between antibiotic resistant intestinal or human associated
bacteria and Caulobacter in the waste water treatment systems.
The significance of these observations is that Caulobacter may
serve as a reservoir of antibiotic resistance genes which then persist
in the environment and be transferred back to human associated
bacteria. One consequence might be a reduced lifetime for antibiotics
used in clinical medicine.
We will take advantage of the fact Caulobacter
can survive during periods of nutrient exhaustion and that they are
stalked to easily distinguished them from other bacteria. We will be
able to isolate them from the environment using fairly unsophisticated
This may be an ideal organism for a medium
to long term environmental study with a senior class. There are
opportunities to demonstrate some of the microbiology ideas and
techniques at Level 1 of the NCEA Science curriculum. This could also
be an ideal organism to demonstrate gene transfer and gene expression
with Year 12 and Year 13 classes (Level 2 and Level 3). Try the
technique outlined below:
We are one of the few Caulobacter
laboratories in the world. Visit Bert Ely's page
for more information on Caulobacter crescentus, the type strain
most commonly used in laboratory studies.