Analysis of the exoproteome of the marine aggregate-inducing bacterium Marinobacter adhaerens HP15 applying MALDI-TOF MS
Heterotrophic bacteria remineralize the majority of particulate organic matter (POM) in the ocean. Burial of POM for millennial time scales is therefore avoided to a large extend, resources like carbon and nitrogen are channeled back to fuel the microbial loop. Bacterial uptake of macromolecules however is limited by the molecules’ sizes. Thus an initial breakdown towards smaller fragments needs to be carried out in the cell exterior. Hydrolases are therefore found attached to the outer membrane or in the adjacent environment. Their activity strongly shapes biogeochemical cycling of elements on a global scale.
The heterotrophic bacterium Marinobacter adhaerens HP15 was found to attach to diatom cells and trigger marine aggregate formation. Initial identification of the extracellular proteome applying MALDI-TOF mass spectrometry has been carried out on a laboratory scale. Future projects aim the knock out of hydrolase genes in HP15 with subsequent phenotype characterization. Bioinformatics approaches will be used for mapping of hydrolase gens among other marine bacteria. Characterization of extracellular proteins may be expanded to further heterotrophic bacteria abundant in marine habitats.
Identification of hydrolases and their source organisms will contribute to a more complete understanding of POM fate and element cycling in the ocean.
Figure left: Transmission electron micrograph of Marinobacter adhaerens HP15; middle: Marine aggregate, providing a hot spot of POM remineralization in marine habitats; right: MALDI-TOF MS spectrum of peptide masses, used for protein identification