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Bacterial diversity in streams


Biofilm bacterial diversity data were collected from samples obtained on seven sampling occasions between September 2004 to July 2006.

For each sampling date, ten similarly sized sample rocks were selected within a 30 m reach of each stream. Biofilm was sampled from the upper surface of each rock and the bacterial community structure and composition characterised by DNA sequence analysis of cloned bacterial 16S rRNA genes.

  • The low impact stream contained a lower abundance of autotrophic cyanobacteria than more highly impacted streams, possibly the consequence of increased shade within the highly forested catchment. In contrast, members of the Betaproteobacteria were most abundant within the least impacted site. Members of the Gammaproteobacteria were abundant within all four streams.


Class-level bacterial diversity in Auckland streams
(click on picture to see chart in full size)
(click here to see this data in table format)

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  • Alphaproteobacteria populations were quite diverse in all streams and generally were a high proportion of the population in less impacted streams.


Alpaproteobacterial diversity in Auckland streams
(click on picture to see chart in full size)
(click here to see this data in table format)

  • Betaproteobacteria populations showed high diversity at all sites and no clear pattern between differently impacted streams.


Betaproteobacterial diversity in Auckland streams
(click on picture to see chart in full size)
(click here to see this data in table format)

  • Gammaproteobacteria occured in all streams and tended to be more numerous in warm seasons. Interestingly, organisms related to the putative pathogenic bacteria Escherichia coli, Legionella, Salmonella and Shigella were commonly detected within all streams, and with no trend in abundance relating to the extent of stream catchment impact. We are currently undertaking further investigations to identify ‘environmental clades’ of E. coli within freshwater aquatic systems (i.e., genetically distinct groups of E. coli with the ability to survive and multiply outside of the intestinal tract).


Gammaproteobacterial diversity in Auckland streams
(click on picture to see chart in full size)
(click here to see this data in table format)

  • Cyanobacteria abundance was higher in streams subjected to greater levels of human impact. In particular, members of the genera Oscillatoria, Anabaena and Aphenizomenon were found in greater number within the medium and highly impacted streams.


Cyanobacterial diversity in Auckland streams
(click on picture to see chart in full size)
(click here to see this data in table format)

  • Summary. Bacterial diversity was high at all sites including the most impacted stream. Few trends in bacterial composition were apparent between sites increasingly impacted by human activity, although the abundance of cyanobacteria was notably greater within the most impacted site.
    In order to further interrogate links between bacterial community organization and level of catchment impact, we are currently devising methods to categorise the abundance and diversity of different ‘functional groups’ of bacteria (such as those characterizing resistance to heavy metals). This will enable the study of differences in bacterial populations with respect to their differing functional attributes. This ongoing work will improve significantly our understanding of the importance of maintaining microbial diversity in streams.
   

 

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Stream Biofilm Research Group
School of Biological Sciences
The University of Auckland
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© Stream Biofilm Project, The University of Auckland 2008-2010
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