Fluorescence characteristics of humic-like fluorescent dissolved organic matter produced by various taxa of marine bacteria

An experimental study was conducted to assess the difference in humic-like fluorescence characteristics (excitation/emission = 290 to 360 /370 to 460 nm) of dissolved organic matter produced by bacteria isolated from coastal seawater. Ten bacterial strains were isolated, and 1 additional strain was obtained from the Japan Collection of Microorganisms. The strains' nearest phylogenetic neighbors were identified using 16S rRNA gene analysis. Eleven bacterial strains were inoculated in experimental liquid medium and incubated for 7 d. In this incubation experiment, the excitation-emission matrixes of the culture media were analyzed to elucidate the production of humic-like fluorescent dissolved organic matter (FDOM) between Day 0 and Day 7 of the incubation. The production of humic-like FDOM was found in 8 of the 11 culture media, with a total of 14 humic-like fluorescence peaks detected. Of these peaks, 10 exhibited different fluorescence characteristics. These findings indicate that the fluorescence characteristics of bacterialderived humic-like FDOM differed among the bacterial groups. Several cultures of bacterial strains contained FDOM, with peaks occurring in the spectral region often associated with humic-like material of terrestrial origin. One bacterial strain showed productivity of humic-like FDOM that was 1 order of magnitude higher than most of the bacterial strains. This result implies that the relative importance of humic-like FDOM production is different among bacterial genera in the ocean.