# Comparative Transcriptomics Reveals Metabolic Adaptations of Priestia megaterium BZ-95 to Different Nitrogen Sources

## TL;DR

This study explores how a bacterium adapts its metabolism to different nitrogen sources, offering insights into sustainable solutions for nitrogen pollution in aquaculture.

## Contribution

The paper reveals novel metabolic strategies of Priestia megaterium BZ-95 under various nitrogen conditions using comparative transcriptomics.

## Key findings

- BZ-95 activates branched-chain amino acid biosynthesis under ammonium.
- Nitrate conditions enhance membrane transport and 2-oxocarboxylic acid metabolism.
- Nitrite stress triggers a coordinated response involving the nir module and energy metabolism.

## Abstract

While intensive aquaculture has developed rapidly, the consequent buildup of nitrogenous compounds, poses a critical threat to aquatic organisms. Microbial degradation offers an environmentally sustainable solution. We investigated the metabolic regulatory capacity of Priestia megaterium BZ-95 under four nitrogen regimes—ammonium (NH4+-N), nitrite (NO2−-N), nitrate (NO3−-N), and a mixture of them (Mix)—using comparative transcriptomics. We revealed that BZ-95 in NH4+-N activated a direct assimilation program prioritizing branched-chain amino acid biosynthesis. Conversely, under nitrate, BZ-95 enhanced membrane transport and 2-oxocarboxylic acid metabolism to facilitate the rapid incorporation of nitrate-derived ammonium into biomass. Nitrite stress triggered a coordinated response involving the assimilatory nir module (nirC-nirB-nirD) and enhanced energy metabolism to meet the heightened demand for reducing power during its rapid reduction. Under mixed nitrogen sources, BZ-95 established a highly synergistic carbon-nitrogen network, simultaneously processing multiple nitrogen inputs without a hierarchical preference, highlighting its remarkable metabolic plasticity. Intersection analysis defined a refined core of 692 nitrite-specific DEGs and revealed broad transcriptional activation under nitrite stress. Analysis of the NO2−-specific core identified enhanced transmembrane transport capacity, coupled with auxiliary metabolic tuning, as central adaptive strategies for nitrite processing. Collectively, these findings provide crucial insights into the molecular basis of nitrogen coordination in P. megaterium BZ-95.