Comparative 16S rRNA amplicon profiling of cattle manure and Lake Van sediment: selective environmental filtering of fecal-associated bacterial communities in a polyextreme soda lake

The agricultural dissemination of livestock-derived fecal microbiota into aquatic ecosystems presents a significant One Health challenge. However, polyextreme environments, such as the highly alkaline and saline Lake Van, are hypothesized to act as natural environmental filters against non-adapted, allochthonous microorganisms. This study evaluated the selective environmental filtering potential of the Lake Van ecosystem against cattle manure inputs. We compared the microbial communities of cattle manure (CM, n = 5) and Lake Van coastal sediment (LS, n = 5) using 16S rRNA gene amplicon sequencing at the strict amplicon sequence variant (ASV) level. The analysis revealed a profound compositional separation between the two compartments (PERMANOVA pseudo-F = 5.21, p = 0.011), with only 8.6% of the 45,842 detected ASVs shared across environments. A sharp alpha diversity contrast in favor of LS was accompanied by a phylum-level inversion between Bacillota (LS-dominant) and Pseudomonadota (CM-dominant). Crucially, classic fecal and zoonotic indicators (Escherichia–Shigella, Enterobacteriaceae, Acinetobacter, Burkholderiaceae, and Streptococcus) exhibited a systematic 3- to 42-fold reduction in the sediment. Conversely, obligately anaerobic Bacillota families, including spore-forming Clostridium, persisted in the LS environment. The polyextreme physicochemical conditions of the soda lake impose a strong environmental filtering effect on manure-derived microbial diversity. While this filter substantially attenuates aerobically-tolerant fecal microbiota, the persistence of strict anaerobes indicates that the filtering effect is selective rather than absolute. The minimal shared-ASV fraction places a strict upper bound on strain-level fecal–sediment connectivity, underscoring the severe selective pressures of the extreme soda-lake environment.