Investigating a lotic microbial community following a severe detergent spill.

A large non-ionic detergent spill affected the Yarqon stream, where water sampling was performed prior to the spill as a part of the stream's routine sampling and during and after the event. Following the spill, a large foam layer was observed for about 3-4 days accompanied by death of all fauna in the stream. Despite a large quantity of freshwater that was introduced to the stream as an emergency measure, a drastic decrease in dissolved oxygen was also observed. A rapid reduction in bacterial diversity and richness, as measured by automated ribosomal intergenic spacer analysis, was also evident, as microbial assemblages changes accompanied pollutant exposure. However, this analysis showed that the microbial assemblages of the stream were quick to recover and became similar to pre-spill communities as early as a week after the spill. These findings suggest that bacterial assemblages are much more robust to large anthropogenic disturbances than expected.

In situ transplant analysis of free-living bacteria in a lotic ecosystem.

The Yarqon is a slow-flowing Mediterranean stream with three ecologically distinct sections, with varying abiotic conditions and anthropogenic influences. We used the Yarqon as a test habitat to study the effect of flow on microbial communities. Stream water samples from three distinct abiotic conditions: "clean", "human-impacted" and "brackish" sections were incubated in situ in dialysis bags at each of these sections for approximately 73 h. The samples were retrieved and analyzed by ARISA (automated ribosomal internal spacer analysis) and viable counts. Diversity estimates showed that free-living assemblages from the middle human-impacted section increased in diversity, while assemblages from the upper-clean section decreased in diversity unless planted in their site of origin. Samples originating from the brackish western section decreased in diversity wherever they were incubated. The ARISA profiles of the samples usually grouped by origin rather than by incubation location, implying that the rate of change of the free-living bacterial assemblages due to the shift in environment is relatively slow. Nevertheless, introducing free-living bacteria from the human-impacted section into the freshwater section resulted in a profile more similar to the latter, indicating a profound niche influence on these microbial assemblages.

Fine-scale temporal dynamics of a fragmented lotic microbial ecosystem.

Microbial ecosystems are often assumed to be relatively stable over short periods of time, but this assumption is seldom tested. An urban stream influenced by both flow and varying levels of anthropogenic influences is expected to have high temporal variability in microbial composition, and short-term ecological instability. Thus, we analyzed the bacterioplankton composition of a weir-fragmented urban stream using Automated rRNA Intergenic Spacer Analysis (ARISA). A total of 46 sequential samples were collected in July 2009 for 7 days, every 7 hours, from both the up-stream side of the weir (stream water) and the downstream side of the weir (estuarine) water. Bray-Curtis similarity based analysis showed a clear division between upstream and downstream communities. A sudden pH drop induced change in both communities, but composition stability partially recovered within less than a day. Thus, our results show that microbial ecosystems can change rapidly, but re-establish a new equilibrium relatively quickly.

Detection of spatial and temporal influences on bacterial communities in an urban stream by automated ribosomal intergenic ribosomal spacer analysis.

The Yarqon is the largest urban river in Israel, and is a slow-flowing stream whose water originates mostly from wastewater treatment plants. Thus, its microbial community is expected to be heavily impacted both by anthropogenic factors and by seasonal temporal variation. In order to identify the main factors that influence the bacterial community, and their spatial-temporal variation, 50 samples were collected representing five different time points and eleven locations. Samples were analyzed for biotic and a-biotic parameters and the bacterial populations were analyzed by Automated Ribosomal Intergenic Spacer Analysis (ARISA). Bacterial richness and diversity were calculated and compared across samples. Canonical Correspondence Analysis (CCA) showed that ARISA clustered the samples according to temporal variation. Molecular fingerprinting analysis provided a snapshot of the microbial community and showed good correlation with geochemical parameters, despite the rapid changes of the Mediterranean environment and the anthropogenic impact. Molecular fingerprinting methods based on natural fragment length polymorphisms may therefore represent a supplementary approach for stream monitoring, alongside physico-chemical measurements.

Composition and dynamics of the gill microbiota of an invasive Indo-Pacific oyster in the eastern Mediterranean Sea.

Gill bacterial communities of Chama pacifica, an Indo-Pacific invasive oyster to the eastern Mediterranean Sea, were compared with those of Chama savignyi, its northern Red Sea congeneric species. Summer and winter bacterial populations were characterized and compared using 16S rDNA clone libraries, and seasonal population dynamics were monitored by automated ribosomal intergenic spacer analysis (ARISA). Clone libraries revealed a specific clade of bacteria, closely related to marine endosymbionts from the Indo-Pacific, found in both ecosystems, of which one taxon was conserved in oysters from both sites. This taxon was dominant in summer libraries and was weakly present in winter ones, where other members of this group were dominant. ARISA results revealed significant seasonal variation in bacterial populations of Mediterranean Sea oysters, as opposed to Red Sea ones that were stable throughout the year. We suggest that this conserved association between bacteria and oyster reflects either a symbiosis between the oyster host and some of its bacteria, a co-invasion of both parties, or both.