High Proline Content of Bacteria-Sized Particles in the Western North Pacific and Its Potential as a New Biogeochemical Indicator of Organic Matter Diagenesis

Hiroyuki Takasu,Toshi Nagata

doi:10.3389/fmars.2015.00110

Abstract

Amino acid (AA) compositions were determined for bacteria-sized particles and particulate organic matter (POM) collected in offshore regions of the western North Pacific. The L-proline content of bacteria-sized particles was remarkably high, accounting for 46 ± 10% (mean ± SD, n =3) of the total quantifiable AA (11 L-AAs and 2 D-AAs were quantified). The L-proline content was much higher than the corresponding values determined for isolated enteric and marine bacterial strains (2–9%). In POM, the L-proline content was low (<5% of total AA) in the upper layer (10–200 m), whereas it was high (20–26% of total AA) at a depth of 1000 m and was accompanied by the enrichment of D-enantiomers of AAs. L-proline enrichment in bacteria-sized particles and deep-water POM suggests a potential use of the L-proline content (mole%) as a new biogeochemical indicator of organic matter diagenesis.

Highlights

Produced organic matter in oceans is extensively altered by microbes and displays amino acid (AA) compositional signature that reflects the extent and nature of complex microbial reworking of organic matter (Keil et al, 2000)
Similar recoveries have been reported in previous studies that used large-volume tangential flow filtration techniques to concentrate natural bacterial assemblages (Benner, 1991; Fukuda et al, 1998)
The procedures used in the concentration process differed among studies, the low recovery has been generally ascribed to the incomplete removal of bacteria that are firmly attached to filters

Summary

INTRODUCTION

Produced organic matter in oceans is extensively altered by microbes and displays amino acid (AA) compositional signature that reflects the extent and nature of complex microbial reworking of organic matter (Keil et al, 2000). Non-protein AAs, including β-alanine, γ-amino butyric acid, and D-enantiomers of AAs are known to be enriched in the organic matter pool, thereby serving as useful indicators of organic matter diagenesis (Cowie and Hedges, 1992; Dauwe et al, 1999; Davis et al, 2009). This diagenetic alteration in AA composition is ascribed to the accumulation of metabolic intermediates (e.g., partial decarboxylation products, Cowie and Hedges, 1994) and to the progressive addition of bacteria-derived organic matter during degradation (Pedersen et al, 2001; Kaiser and Benner, 2008; Davis et al, 2009). We examined depth-dependent (10–1000 m) changes in the AA composition of particulate organic matter (POM) collected in offshore waters of the western North Pacific

MATERIALS AND METHODS

RESULTS

Findings

DISCUSSION