# Arctic Diatoms as a Source of Antibiofilm Compounds: Identification of Methyl 3-Hydroxyoctadecanoate and Pheophorbide a

## TL;DR

Arctic diatoms, like Porosira glacialis, produce compounds that inhibit biofilm formation without toxicity, offering potential for sustainable antibiofilm agents.

## Contribution

Identification of methyl 3-hydroxyoctadecanoate and pheophorbide a as novel antibiofilm compounds from Arctic diatoms.

## Key findings

- Porosira glacialis showed strong antibiofilm activity against Staphylococcus epidermidis with no cytotoxicity.
- Methyl 3-hydroxyoctadecanoate is a new antibiofilm compound first reported in diatoms.
- Cylindrotheca closterium's antibiofilm activity depends on cultivation conditions.

## Abstract

Marine diatoms are prolific producers of bioactive metabolites, but Arctic species remain underexplored as sources of antibacterial and antibiofilm agents. Here, seven species were grown in photobioreactors (PBRs) and systematically screened for antibacterial, antibiofilm, and cytotoxic activities. All strains inhibited Gram-positive bacteria, and four reduced Staphylococcus epidermidis biofilm formation. Porosira glacialis emerged as a lead species, combining potent antibiofilm activity with favourable traits for large-scale cultivation, and no detectable cytotoxicity. Bioactivity-guided fractionation of P. glacialis yielded two antibiofilm compounds: methyl 3-hydroxyoctadecanoate, the first time reported in diatoms and newly associated with antibiofilm bioactivity, and pheophorbide a, a chlorophyll degradation product. Both inhibited S. epidermidis biofilm formation without any observed cytotoxicity. Notably, Cylindrotheca closterium exhibited cultivation-dependent antibiofilm activity, underscoring the importance of growth conditions for metabolite production. These findings highlight the potential of Arctic diatoms as a sustainable source of antibiofilm agents and support further exploration of their metabolites for antimicrobial and industrial applications.