Sosa Oscar A, Repeta Daniel J, Ferrón Sara, Bryant Jessica A, Mende Daniel R, Karl David M, DeLong Edward F
Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawaii, Honolulu, HI, United States.
Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI, United States.
Front Microbiol. 2017 Sep 26;8:1786. doi: 10.3389/fmicb.2017.01786. eCollection 2017.
Semi-labile dissolved organic matter (DOM) accumulates in surface waters of the oligotrophic ocean gyres and turns over on seasonal to annual timescales. This reservoir of DOM represents an important source of carbon, energy, and nutrients to marine microbial communities but the identity of the microorganisms and the biochemical pathways underlying the cycling of DOM remain largely uncharacterized. In this study we describe bacteria isolated from the North Pacific Subtropical Gyre (NPSG) near Hawaii that are able to degrade phosphonates associated with high molecular weight dissolved organic matter (HMWDOM), which represents a large fraction of semi-labile DOM. We amended dilution-to-extinction cultures with HMWDOM collected from NPSG surface waters and with purified HMWDOM enriched with polysaccharides bearing alkylphosphonate esters. The HMWDOM-amended cultures were enriched in Roseobacter isolates closely related to and close relatives of hydrocarbon-degrading bacteria of the family, many of which encoded phosphonate degradation pathways. cultures encoding C-P lyase were able to catabolize methylphosphonate and 2-hydroxyethylphosphonate, as well as the esters of these phosphonates found in native HMWDOM polysaccharides to acquire phosphorus while producing methane and ethylene, respectively. Conversely, growth of these isolates on HMWDOM polysaccharides as carbon source did not support robust increases in cell yields, suggesting that the constituent carbohydrates in HMWDOM were not readily available to these individual isolates. We postulate that the complete remineralization of HMWDOM polysaccharides requires more complex microbial inter-species interactions. The degradation of phosphonate esters and other common substitutions in marine polysaccharides may be key steps in the turnover of marine DOM.
半不稳定溶解有机物（DOM）在贫营养海洋环流的表层水中积累，并在季节性到年度的时间尺度上周转。这种DOM库是海洋微生物群落碳、能量和营养的重要来源，但参与DOM循环的微生物身份和生化途径在很大程度上仍未得到表征。在本研究中，我们描述了从夏威夷附近的北太平洋亚热带环流（NPSG）分离出的细菌，这些细菌能够降解与高分子量溶解有机物（HMWDOM）相关的膦酸盐，HMWDOM占半不稳定DOM的很大一部分。我们用从NPSG表层水收集的HMWDOM和富含带有烷基膦酸酯多糖的纯化HMWDOM对稀释至灭绝培养物进行了改良。用HMWDOM改良的培养物中富集了与红杆菌属密切相关的分离株，以及属于 科的烃降解细菌的近亲，其中许多编码膦酸盐降解途径。编码C-P裂解酶的培养物能够分解甲基膦酸盐和2-羟乙基膦酸盐，以及在天然HMWDOM多糖中发现的这些膦酸盐的酯，分别获取磷并产生甲烷和乙烯。相反，这些分离株在HMWDOM多糖作为碳源上的生长并不能支持细胞产量的强劲增加，这表明HMWDOM中的组成碳水化合物对这些单个分离株来说不易获得。我们推测，HMWDOM多糖的完全再矿化需要更复杂的微生物种间相互作用。海洋多糖中膦酸酯和其他常见取代基的降解可能是海洋DOM周转的关键步骤。
