Marine microbial aggregating macromolecules: Potential mediators of coastal carbon flux

Abstract

Microbial aggregation‐adhesion enhancing macromolecules (AAEM) in high molecular weight materials (HMWM) recovered from coastal seawater, suspended particulates and sediments were isolated using immunoaffinity chromatography. The quantity of AAEM recovered was an order of magnitude higher in suspended particulates compared to seawater and sediments. However, the AAEM/HMWM ratio remained constant in samples from all three sources. The fulvic acid component of suspended particulates had 91% of the AAEM, compared to 59% in the sediments. This change in AAEM distribution was directly correlated with decreased amounts of the predominant AAEM molecular size present in the sediment samples. Spectroscopic (FTIR) analyses revealed that the reduction in the relative quantities of fulvic acid AAEM in the sediment was most likely due to oxidative degradation of these residues. While significant adhesion enhancement activity was detected in both fulvic and humic acid AAEM fractions in sediments, the fulvic acid AAEM was significantly more active than the humic acid component. Fulvic and humic acid AAEM activity was strongly conserved in sediments despite reductions in quantity and oxidative degradation, indicating that these materials may play an important role in microbial organic carbon flux in this tropical coastal marine environment.