Khanhmeter K01: A Low-Cost rrn-Based Resilience Proxy for Drinking Water Under Salinity Intrusion – A Concept and Open Validation Protocol

Salinity intrusion threatens drinking water security in the Mekong Delta, where monitoring remains dominated by physicochemical sensors. Recent perspectives on the microbial "unknome" (Vaccaro et al., 2026, Heredity) emphasize that 40-60% of protein-coding genes in metagenomes remain functionally uncharacterized (Vanni et al., 2022), many of which mediate biotic interactions and stress responses that are missed in pure cultures. Building on this ecological view, and on the established relationship between 16S rRNA operon (rrn) copy number and life-history strategy (Klappenbach et al., 2000; Stoddard et al., 2015), we propose Khanhmeter K01. We define the Khanh-Index (K-Index) as a low-cost, taxonomy-informed proxy for community recovery potential after a salt pulse, based on the ratio of copiotrophic to oligotrophic taxa weighted by mean rrn copy number from rrnDB (Stoddard et al., 2015; 2023). This manuscript presents only a concept and a fully open, 0-cost in silico validation protocol using public NCBI Sequence Read Archive (SRA) data (Kodama et al., 2012), SILVA 138, and rrnDB v5.9. No experimental validation is claimed here. All code is designed for Google Colab.