Predictive functional converge after nitrate input
In FAPROTAX, most OTUs (> 90.7%) failed to associate with
either N- or S-metabolism. In the absence of favorable electron
acceptors, control communities were rich in methanogens (Figure S5A),
which were archaea in the phylum Euryarchaeota . The number of
putative nitrate reducers (e.g., members of genus Nitrospira ,Bacillus, Paracoccus ) and sulfate reducers (e.g., members of
genus Syntrophobacter , Desulfococcus ,Desulfobulbus , Desulfovibrio ) were comparable (Figure S5B,
S5C). For nitrate communities, the number of putative nitrate reducers
kept decreasing, which contradicted the drastic nitrate reduction
possibly because the actual nitrate reducers were yet to be collected in
the FAPROTAX database. Members of genus Thiobacillus ,Paracoccus , Sulfuricurvum or Acidithiobacillus were
putative AVS oxidizers and Thiobacillus in particular, was
assigned to dark-sulfide-oxidation and
dark-oxidation-of-sulfur-compounds.
In PICRUSt, we focused on the changes of gene copy number based on a
normalized PICRUSt table (KEGG Orthology Level 2 and 3). Each sample was
rarefied to an equal sum of predicted gene copies so that the copy
number of each functional item represented its strength. When analyzing
the general metabolism (ko09100, Level 2), the late nitrate communities
(16-N and 32-N) exhibited the greatest difference from the rest. Five
orthologues (ko09102, 09104, 09106-09108) were enriched and four
(ko09101, 09109-09111) were suppressed (Figure 4). Within ko09102
(energy metabolism), nitrogen metabolism had higher background
abundances (~25000 copies per community) than sulfur
metabolism (~10500) and were more enriched after nitrate
amendment (Figure S5E, S5F).