Eukaryotic diversity at pH extremes

Abstract

Extremely acidic (pH < 3) and extremely alkaline (pH > 9) environments support a diversity of single-cell and to a lesser extent, multicellular eukaryotic life. This study compared alpha and beta diversity in eukaryotic communities from seven diverse aquatic environments with pH values ranging from 2 to 11 using massively-parallel pyrotag sequencing targeting the V9 hypervariable region of the 18S ribosomal RNA (rRNA) gene. A total of 946 operational taxonomic units (OTUs) were recovered at a 6% cut-off level (94% similarity) across the sampled environments. Hierarchical clustering of the samples segregated the communities into acidic and alkaline groups. Similarity percentage (SIMPER) analysis followed by indicator OTU analysis (IOA) and non-metric multidimensional scaling (NMDS) were used to determine which characteristic groups of eukaryotic taxa typify acidic or alkaline extremes and the extent to which pH explains eukaryotic community structure in these environments. Spain's Rio Tinto yielded the fewest observed OTUs while Nebraska Sandhills alkaline lakes yielded the most. Distinct OTUs, including metazoan OTUs, numerically dominated pH extreme sites. Indicator OTUs included the diatom Pinnularia and unidentified opisthokonts (Fungi and Filasterea) in the extremely acidic environments, and the ciliate Frontonia across the extremely alkaline sites. Inferred from NMDS, pH explained only a modest fraction of the variation across the datasets, indicating that other factors influence the underlying community structure in these environments. The findings from this study suggest that the ability for eukaryotes to adapt to pH extremes over a broad range of values may be rare, but further study of taxa that can broadly adapt across diverse acidic and alkaline environments, respectively present good models for understanding adaptation and should be targeted for future investigations.

Microbes in mercury-enriched geothermal springs in western North America

“…Neutral-alkaline springs have consistently higher microbial diversity than acid springs, and acid spring communities are distinct from those in neutral and alkaline springs regardless of temperature (Sharp et al, 2014). Alkaline environments support greater algal diversity than acidic habitats, and diversity decreases regardless of pH when heavy metal concentrations are high (Amaral-Zettler, 2013). In general, the more extreme the environmental conditions, the lower the microbial diversity.…”

Rotifers in Lake Orta: a potential ecological and evolutionary model system

“…On the other hand, no rotifer community is usually found in the plankton of lakes at pH>10, if not for the occasional occurrence of one species of Brachionus (Pejler, 1974). Rotifer communities at these extreme values, with pH <3 or >10, are very poor and usually host only one or two species (Weithoff, 2005;Moser and Weisse, 2011;Amaral-Zettler, 2012).…”

Ciliates in Extreme Environments

“…). However, at the present state of knowledge, only a few studies demonstrated the occurrence of planktonic ciliates in alkaline environments (e.g., Amaral‐Zettler ; Esteban et al. ; Finlay et al.…”

“…Very recently, Amaral‐Zettler () studied eukaryotic alpha and beta diversity in eukaryotic communities from seven diverse aquatic environments with pH values ranging from 2 to 11. An unidentified Cyclidium species was observed in the biofilm/sediment sample (pH 10.4) from Mallard Lake, Sandhills NE, USA.…”