Potential quality indicators detected in all three domains of
life
The potential of microbial community members as indicators of ecosystem
quality has previously been shown in contaminated sediments and marine
environments (Acosta-González & Marqués, 2016; Urakawa et al., 2012),
as well as rivers (Li et al., 2018). The strongest correlation to
ecological status among the individual domains was observed in the ZOTUs
from the bacterial community. Furthermore, correlations of interest fromArchaea and Eukaryotic ZOTUs were also observed (Figure 3,
S6 and S7)), but these were weaker compared to the Bacteria . The
latter correlations may be affected by their relatively low abundance in
the bulk samples, and may be more significant when implemented in a
network based approach targeting cross-domain interactions as indicators
of quality, due to the complex nature of stream ecosystems (Battin et
al., 2016).
Bacterial communities have previously been shown to reflect
environmental changes relating to land use (Lear et al., 2013), as well
as (anthropogenic) pollution (Acosta-González & Marqués, 2016;
Mlejnková & Sovová, 2010; Urakawa et al., 2012). Organisms previously
reported in relation to ecosystem health were found among the potential
indicator OTUs of the prokaryotes. The genus Flavobacterium was
observed among the ZOTUs associated to lower quality streams, and has
previously been linked to anthropogenic activity in surface waters
(Acosta-González & Marqués, 2016; Mlejnková & Sovová, 2010). A
positive correlation was observed between the ecological status and a
representative of the family Nitrosomonadaceae and the genusNitrospira . This correlation has previously been characterized in
a marine ecosystem in which pollution was shown to induce significant
changes in the nitrifying communities (Urakawa et al., 2012). Similar
observations have described for increased abundances of the familyRhodobacteraceae exposed to oil pollution in sediments
(Acosta-González & Marqués, 2016), however the indicator analysis in
the present study yielded multiple ZOTUs representing this family, but
with opposing tendencies. This highlights the importance of taxonomic
resolution, as a family of bacteria can contain numerous of species with
a wide range of functions and sensitivity to their environment.
Analysis of the microbial communities, and its vast diversity, present
in stream bulk samples could provide an interesting supplement to
existing metabarcoding approaches targeting biomarkers for eukaryotes
such as the COI gene (Kuntke et al., 2020). Now, when applying a
molecular approach for water quality assessment we are no longer limited
to the composition of visible BQE´s, such as macroinvertebrates. The
microbial community composition in the streams may often capture a
better and more comprehensive and sensitive snapshot of the diversity in
stream waters.