High molecular weight dissolved organic matter enrichment selects for methylotrophs in dilution to extinction cultures
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DeLong_High molecular.pdf
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Author(s)
Sosa, Oscar Abraham
Gifford, Scott M.
Repeta, Daniel J.
DeLong, Edward Francis
Date Issued
May 2015
Journal
The ISME Journal
Publisher
Nature Publishing Group
Citation
Sosa, Oscar A, Scott M Gifford, Daniel J Repeta, and Edward F DeLong. “High Molecular Weight Dissolved Organic Matter Enrichment Selects for Methylotrophs in Dilution to Extinction Cultures.” ISME J 9, no. 12 (May 15, 2015): 2725–2739. © 2015 International Society for Microbial Ecology
Version
Final published version
Abstract
The role of bacterioplankton in the cycling of marine dissolved organic matter (DOM) is central to the carbon and energy balance in the ocean, yet there are few model organisms available to investigate the genes, metabolic pathways, and biochemical mechanisms involved in the degradation of this globally important carbon pool. To obtain microbial isolates capable of degrading semi-labile DOM for growth, we conducted dilution to extinction cultivation experiments using seawater enriched with high molecular weight (HMW) DOM. In total, 93 isolates were obtained. Amendments using HMW DOM to increase the dissolved organic carbon concentration 4x (280 μM) or 10x (700 μM) the ocean surface water concentrations yielded positive growth in 4–6% of replicate dilutions, whereas <1% scored positive for growth in non-DOM-amended controls. The majority (71%) of isolates displayed a distinct increase in cell yields when grown in increasing concentrations of HMW DOM. Whole-genome sequencing was used to screen the culture collection for purity and to determine the phylogenetic identity of the isolates. Eleven percent of the isolates belonged to the gammaproteobacteria including Alteromonadales (the SAR92 clade) and Vibrio. Surprisingly, 85% of isolates belonged to the methylotrophic OM43 clade of betaproteobacteria, bacteria thought to metabolically specialize in degrading C1 compounds. Growth of these isolates on methanol confirmed their methylotrophic phenotype. Our results indicate that dilution to extinction cultivation enriched with natural sources of organic substrates has a potential to reveal the previously unsuspected relationships between naturally occurring organic nutrients and the microorganisms that consume them.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
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DOI of Published Version
https://doi.org/10.1038/ismej.2015.68
