Succession and Diel Transcriptional Response of the Glycolate-Utilizing Component of the Bacterial Community during a Spring Phytoplankton Bloom

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Abstract
The influence of the phytoplankton-specific organic compound glycolate on bacterial community structure was examined during the 2004 spring phytoplankton bloom (February to April) in Dabob Bay in Washington. The diversity of the bacteria able to utilize glycolate during the phytoplankton bloom was determined using previously developed PCR primers to amplify the gene for the D subunit of glycolate oxidase ( glcD ). Many of the glcD sequences obtained represented novel sequences that appeared to be specific to marine environments. Overall, the glcD sequence diversity decreased as the phytoplankton bloom progressed. Phylotype-specific glcD quantitative PCR primers were designed for the six most commonly detected glcD phylotypes that represented distinct phylogenetic groups of heterotrophic bacteria. Three patterns of phylotype abundance were detected: four phylotypes were most abundant during the onset of the bloom; the abundance of one phylotype increased as the bloom progressed; and one phylotype was abundant throughout the bloom. Quantitative reverse transcriptase PCR with the same phylotype-specific primers was used to determine the levels of day and night glcD RNA transcription over the course of the bloom. glcD transcripts, when detectable, were always more abundant in the day than at night for each phylotype, suggesting that the bacteria responded to the glycolate produced by phytoplankton during the day. The nearly constant low in situ glycolate concentrations suggested that bacteria rapidly utilized the available glycolate. This study provided evidence for direct phytoplankton-bacterium interactions and the resulting succession in a single functional group of marine bacteria.

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