BROADENING THE TARGETS FOR MICROBIAL WATER QUALITY
HOW THE CLOSE ASSOCIATION BETWEEN BACTERIA COMMUNITY COMPOSITION AND ELEVATED NUTRIENTS IN ESTUARIES COULD BE EXPLOITED TO SELECT A RANGE OF WATER QUALITY INDICATORS
K Gibb, M Kaestli, J Smith, K McGuinness
Publication Date (Web): 12 April 2016
DOI: https://doi.org/10.21139/wej.2016.019


DNA technologies give us an unprecedented opportunity to broaden microbial water quality targets for routine monitoring. It is now well understood that the conventional indicators Escherichia coli and enterococci can survive and be detected in a variety of non-faecal sources, making it difficult to monitor human faecal pollution in receiving environments. The call for broadening the targets for water quality assessment has also been driven by the application of next-generation sequencing (NGS) to environmental samples, which has allowed significant advances in our understanding of bacterial community dynamics. NGS has created an unprecedented inventory of microbial communities associated with faecal sources, allowing re-examination of which taxonomic groups are best suited as indicators.

While these new approaches have opened the door to ecological-scale microbial assessment, we still have much to learn about how microbial communities respond to disturbance. If their response to nutrient gradients, for example, is highly variable both temporally and spatially, then their value as a source of new indicators might be questionable. There are also many regions and ecosystems for which we have no community level microbial data, from which we can pose informed questions about ecosystem health and processes. Darwin Harbour is one such region, so our aim was to compare the bacterial community composition in sewage effluent impacted and control creeks with no sewage effluents. From this baseline knowledge we aimed to increase our understanding of what makes the bacterial communities different – and, if in fact they are, what the implications might be for monitoring.

We found that the microbial community was more diverse at the site with the highest level of nutrients and diversity decreased with decreasing levels of nutrients. Taxa such as Aeromonas, Azomonas (see figure) and cyanobacteria have potential as water quality indicators. The Enterobacteriales were interesting: this family contains taxa used in conventional water quality assessment including Salmonella, Escherichia coli, Enterobacter and Klebsiella. However, some members of this order also include environmental bacteria and, indeed, in our study two Enterobacteriales sequences were detected at all sites. Our NGS approach has provided more baseline microbial information for Darwin Harbour, and has identified targets for broader public health and ecosystem health monitoring.



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