Abstract: Filamentous phages are widely distributed in the ocean, and their interactions with bacterial hosts have important biological significance. In this study, we used a strain of Pseudoalteromonas nigrifaciens SCSIO 43210 (designated Pn43210) isolated from the Arctic region as the research object. We found that the biofilm formed under oligotrophic conditions at 15°C began to degrade on the third day of culture, whereas the biofilm formed at 25°C remained intact. Through genome resequencing, transcriptome sequencing, and functional validation, we preliminarily revealed the molecular mechanism underlying this temperature-dependent biofilm degradation. Specifically, low temperature activated two tandem identical copies of a filamentous prophage in the host genome. We also identified a gene with potential excisionase function. A toxin‑antitoxin system (BrnT/BrnA) located in the prophage flanking region was significantly upregulated in biofilm cells. BrnT exhibited cytotoxicity, and BrnA completely counteracted this toxicity. This study provides initial insights into the molecular pathway by which low temperature regulates biofilm degradation through activation of the filamentous prophage and its adjacent toxin‑antitoxin system inPseudoalteromonas. These findings offer new perspectives on the cold‑adaptation strategies of polar microorganisms.

Key words: Pseudoalteromonas, filamentous phage, temperature, biofilm