Where oil eating bacteria thrive across two busy coastal bays

Tiny cleanup crews

Coastal waters face a constant trickle of fuel from towns and factories. Natural oil eating bacteria live in these bays and break down toxic fuel before it floats out to sea. These coastal bays mix fresh river flow with ocean brine. Salt levels rise and fall with rain and tides. Do these tiny cells clean up fuel everywhere, or do they thrive in certain zones?

Reading active genes

A research team collected surface water from the Delaware and Chesapeake Bays. They pieced together mixed DNA into MAGs, or metagenome-assembled genomes, which are full genomes built from wild community DNA. They also looked at metatranscriptomes, the pool of active RNA that shows which genes are switched on. By watching genes that digest fuel, the team tracked how cells respond as salt, warmth, nitrate, and silicate change. This method matters because it shows which cells are working, rather than just listing who lives there.

Varying tools for changing waters

Natural cleanup is not spread evenly across bay waters. It changes with the season, the microbe family, and the water mix. Genes that use oxygen to break down fuel peaked in warm, less salty water during spring and summer. The highest activity for breaking tough ring-shaped fuel molecules occurred in low-salt zones.

Microbes also use distinct survival tactics. In the order Burkholderiales, cells show condition-dependent metabolic coupling, linking their pathways to react to the surrounding water. Meanwhile, the order Pseudomonadales links fuel breakdown directly to central growth and fermentation. Simple cleanup tasks like catechol breakdown showed high functional redundancy, meaning many kinds of microbes can perform the job. But breaking down tough naphthalene was restricted to only a few specialists.

What remains unknown

This work only looked at surface waters across two bays. Spotting switched-on genes shows what cells can digest, but it cannot clock true cleanup speeds in real time. We do not yet know how future climate shifts in warmth and salt will change total cleanup speeds along these shores.