Caulobacter crescentus. Christine Fenton Photo by Christine Fenton

Caulobacter crescentus. 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.

Gene Smugglers?

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.

Detective work

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 techniques.

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:

School Experiments

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.

Visit the National Center for Biotechnology Information to download GenBank genetic sequences for the New Zealand Caulobacter isolates under the following accession numbers:

freshwater isolate TS1 - L41814
Caulobacter cells showing the stalk and  holdfast at the end
freshwater isolate MR1 - L41813
sewage isolate CDF0 - L41812
sewage isolate CDF20a - L41811
sewage isolate CDF35 - L41810

Using a light microscope to examine water samples being enriched for Caulobacter species

A Year 11 NRG student examining New Zealand North Island water supplies for the presence of Caulobacter



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