Urine Bacterial Community Convergence through Fertilizer Production: Storage, Pasteurization, and Struvite Precipitation

Source-separated
human urine was collected from six public events
to study the impact of urine processing and storage on bacterial community
composition and viability. Illumina 16S rRNA gene sequencing revealed
a complex community of bacteria in fresh urine that differed across
collection events. Despite the harsh chemical conditions of stored
urine (pH > 9 and total ammonia nitrogen > 4000 mg N/L), bacteria
consistently grew to 5 ± 2 × 108 cells/mL. Storing
hydrolyzed urine for any amount of time significantly reduced the
number of operational taxonomic units (OTUs) to 130 ± 70, increased
Pielou evenness to 0.60 ± 0.06, and produced communities dominated
by Clostridiales and Lactobacillales. After 80 days of storage, all six urine samples from different
starting materials converged to these characteristics. Urine pasteurization
or struvite precipitation did not change the microbial community,
even when pasteurized urine was stored for an additional 70 days.
Pasteurization decreased metabolic activity by 50 ± 10% and additional
storage after pasteurization did not lead to recovery of metabolic
activity. Urine-derived fertilizers consistently contained 16S rRNA
genes belonging to Tissierella, Erysipelothrix, Atopostipes, Bacteroides, and many Clostridiales OTUs; additional experiments must determine whether pathogenic species
are present, responsible for observed metabolic activity, or regrow
when applied.