Microbial characteristics of Palau Jellyfish Lake

Microbiological examinations of total bacterial population, culturable aerobic heterotrophs, photosynthetic bacteria, and particulate DNA were carried out in Palau Jellyfish Lake. A 2 m thick bacterial plate layer at 13–15 m depth consisting of various components of microbes was observed in Jellyfish Lake. Photosynthetic bacteria, as seen by flow cytometry, were concentrated at 14–15 m depths with a maximal count of 2.2 × 105 cells∙mL−1 and microscopic analysis confirmed that these purple bacteria were Chromatium sp. Peaks in total bacterial counts (8.3 × 106 cells∙mL−1; 13 m), in the Synechococcus spp. population (2.4 × 106 cells∙mL−1; 13 m), in culturable heterotrophs (105 colony-forming units∙mL−1; 15 m), and in particulate DNA (17.8 μg∙L−1; 10 m) were observed either at the bacterial plate layer that was rich in nutrients or just above this layer in the oxic zone. Bacteriochlorophyll and chlorophyll a exhibited peaks at the photosynthetic bacterial plate (14–15 m). A high concentration of particulate organic carbon was also observed at 15 m. The particulate DNA showed a high degree of correlation with the total bacterial cell number. A low ratio of particulate DNA to particulate organic carbon (0.005) in the water column was found at 15 m and suggested that the particulate materials produced by photosynthetic bacteria would have influenced the concentration of particulate organic carbon. Culturable heterotrophs, clustered into nine different groups, were dominated by species of the genera Vibrio, Aeromonas, and Halomonas.