Depolymerization and decomplexation of soil humic acids by an Antarctic Pseudomonas strain

Abstract

With recent rapid warming in the maritime Antarctic, the susceptibility of soil organic matter to microbial decomposition is an emerging topic related to CO2 emission and vegetation changes. Soil humic acids (HA) enter the Antarctic ecosystems as small-soluble organic compounds resulting from microbial decomposition. Antarctic and commercial HAs were incubated with Antarctic Pseudomonas sp. PAMC 29040 with an esterase activity and structural changes in the resulting HA samples were then investigated. Gel permeation chromatography revealed the depolymerization of the large molecular fractions of both Antarctic and commercial HAs. Solid-state 13C-nuclear magnetic resonance spectroscopy showed an increase in the aromaticity degree which can be attributed to the increased intensity of aromatic-C signals upon the cleavage of interior C？C and C？O？C linkages (e.g., decomplexation by esterase activity), while the Fourier-transform infrared spectroscopy did not provide any information on the changes in the functional groups, such as Ar？OH and Ar？COOH, or bonding patterns in the HAs. To the best of our knowledge, this is the first report showing direct evidence of HA decomposition capacity by soil bacteria in an Antarctic terrestrial ecosystem.