Aim The extent to which bacterial communities exhibit biogeographic patterns in their distribution remains unclear. We examined the relative influence of factors including geographic distance, latitude, elevation and catchment land use on the distribution and taxon richness of stream bacterial communities across New Zealand. Location Bacterial communities were collected from biofilm growing on submerged rocks in 244 streams. Sample sites spanned a north–south gradient of over 970 km, an elevational gradient of c. 750 m and were collected from a variety of catchment types across New Zealand. Methods We used automated ribosomal intergenic spacer analysis, a DNA fingerprinting technique, to characterize the structure and taxon richness of each bacterial community. Key attributes relating to sample location, upstream catchment land use and a suite of additional environmental parameters were collected for every site using GIS procedures. Univariate correlations between measures of bacterial community structure and latitude, elevation and distance were examined. Variance partitioning was then used to assess the relative importance of purely spatial factors versus catchment land use and environmental attributes for determining bacterial community structure and taxon richness. Results Bacterial taxon richness was related to the geographic location of the sample site, being significantly greater at latitudes closer to the equator and reduced at higher elevations. We observed distance decay patterns in bacterial community similarity related to geographic distance and latitudinal distance, but not to elevational distance. Overall, however, bacterial community similarity and taxon richness was more closely related to variability in catchment land use than to climatic variability or geographic location. Main conclusion Our data suggest that stream biofilm communities across New Zealand are more influenced by catchment land use attributes than by dispersal limitation.

Summary In stream ecosystems, bacterial communities play an important role in nutrient and energy cycling processes as they are among the most numerous and active organisms at the basal trophic level of the stream food web. Bacterial communities in stream biofilms have been shown to correlate well with different catchment land use and therefore provide an opportunity for the development of a novel ecological indicator of stream ecosystem health. In this study, a bacterial community index (BCI) model was developed and validated using a national data set of biofilm bacterial community profiles collected from 223 streams across seven geographical regions in New Zealand. The six‐component BCI model was generated using the partial least squares regression method to associate the multivariate bacterial community profile with the macroinvertebrate community index, which is a well‐established indicator of stream health. Despite strong regional clustering of the bacterial community profiles, the BCI was indicative of the level of disturbance in the catchment, as shown by significant correlations with a wide range of independent indicators of water quality, macroinvertebrate community data, ecosystem functioning and catchment land‐use data. The BCI was able to explain 35% of the variation in a multi‐metric index incorporating ten common ecological parameters, suggesting that the stream bacterial communities could provide useful information about the ecosystem integrity. The BCI provides a novel ecosystem assessment tool, which can be used to complement existing stream health measures in the management of anthropogenic impacts on freshwater streams and rivers.

Summary We investigated the resident bacterial communities within the biofilm of 252 streams in New Zealand with the aim of assessing the community variation associated with natural and anthropogenic‐influenced environmental characteristics. This work is part of a larger project investigating the use of bacterial communities as biological indicators, and here we assess how predictable the variation in bacterial community is in response to environmental influences. Samples of epilithic biofilm were collected in the Austral Summer of 2010, and bacterial communities were characterised using the DNA‐fingerprinting technique automated ribosomal intergenic spacer analysis (ARISA). Multivariate analysis of the ARISA data revealed that geographical location (region) was a better predictor of bacterial community structure than land use. Our finding that taxon richness varied with geographical location, decreasing along a north to south (increasing latitude) gradient, and that land use had no significant effect on taxon richness suggests that bacterial communities have great potential to act as biological indicators of stream health. In particular, the maintenance of taxon richness at impacted sites is a key advantage since the local extinction of many traditional indicator organisms, such as fish or macroinvertebrates, often precludes their further use. Our conceptual model of bacterial community structure proposes that stream biofilm communities are comprised of four broad groups of bacteria: ubiquitous bacteria (found at all sites), region‐specific bacteria (those representative of geographical areas), natural‐state bacteria (those associated with unmodified systems) and impact‐related bacteria (those associated with human activities). The proportion of these four groups at a particular sample site would provide the basis of a novel bacterial community index of stream health.

The non-protein amino acid 3,4-dehydro-L-proline (DHP) significantly reduced the incidence of fire blight infection on immature pear fruits infected with wildtype Erwinia amylovora. DHP also inhibited biofilm formation in both streptomycin-sensitive and -resistant strains of E. amylovora and induced dispersal of preformed biofilms in the streptomycinsensitive strain. The investigations shed light on the hitherto undiscovered ability of DHP to inhibit bacterial biofilms and its potential as a chemical control option for fire blight.

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