Light-induced aggregation of microbial exopolymeric substances.

Area of Science:

• Marine organic geochemistry
• Biogeochemistry
• Polymer science

Background:

• Sunlight typically breaks down marine colloids, but some biomolecules can aggregate via photo-oxidation.
• The role of light in marine aggregate formation, particularly for bacterial exopolymeric substances (EPS), is not fully understood.

Purpose of the Study:

• To investigate whether sunlight can induce aggregation of marine bacterial EPS.
• To identify the key components and mechanisms involved in light-induced EPS aggregation.

Main Methods:

• Irradiation experiments on exopolymeric substance (EPS) from the marine bacterium Sagitulla stellata.
• Turbidity measurements and flow cytometry to assess particle size and aggregation.
• Analysis of aggregate mass and composition (protein-to-carbohydrate ratio).

Main Results:

• Sunlight irradiation significantly increased EPS turbidity and particle size compared to dark controls.
• Irradiated samples showed a higher mass of collected aggregates.
• Proteins were identified as the key component in light-induced aggregation, with reactive oxygen species and salts playing critical roles.

Conclusions:

• Sunlight can induce the aggregation of protein-rich marine bacterial EPS.
• This light-induced aggregation process, mediated by proteins, influences marine snow formation and the fate of oceanic organic carbon and nitrogen.
• Findings contrast with non-proteinaceous phytoplankton EPS, highlighting the importance of protein content in light-driven aggregation.