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BackgroundDinoflagellate cysts (i.e., dinocysts) are biologically and ecologically important as they can help dinoflagellate species survive harsh environments, facilitate their dispersal and serve as seeds for harmful algal blooms. In addition, dinocysts derived from some species can produce more toxins than vegetative forms, largely affecting species through their food webs and even human health. Consequently, accurate identification of dinocysts represents the first crucial step in many ecological studies. As dinocysts have limited or even no available taxonomic keys, molecular methods have become the first priority for dinocyst identification. However, molecular identification of dinocysts, particularly when using single cells, poses technical challenges. The most serious is the low success rate of PCR, especially for heterotrophic species.MethodsIn this study, we aim to improve the success rate of single dinocyst identification for the chosen dinocyst species (Gonyaulax spinifera,Polykrikos kofoidii,Lingulodinium polyedrum,Pyrophacus steinii, Protoperidinium leonisandProtoperidinium oblongum) distributed in the South China Sea. We worked on two major technical issues: cleaning possible PCR inhibitors attached on the cyst surface and designing new dinoflagellate-specific PCR primers to improve the success of PCR amplification.ResultsFor the cleaning of single dinocysts separated from marine sediments, we used ultrasonic wave-based cleaning and optimized cleaning parameters. Our results showed that the optimized ultrasonic wave-based cleaning method largely improved the identification success rate and accuracy of both molecular and morphological identifications. For the molecular identification with the newly designed dinoflagellate-specific primers (18S634F-18S634R), the success ratio was as high as 86.7% for single dinocysts across multiple taxa when using the optimized ultrasonic wave-based cleaning method, and much higher than that (16.7%) based on traditional micropipette-based cleaning.DiscussionThe technically simple but robust method improved on in this study is expected to serve as a powerful tool in deep understanding of population dynamics of dinocysts and the causes and consequences of potential negative effects caused by dinocysts.

This study investigated the nutrients and heavy metal contents in water body and sediment of the Napahai Wetland during summer through fluorescence spectroscopy and inductively coupled plasma optical emission spectrometer analysis. Results indicated that most of the heavy metal contents in water body are derived from municipal sewage when the stream passes through the town center. The primary organic compounds in the water body of the Nachi River and the Napahai Wetland were hydrophobic acid, fulvic acid, and aromatic protein-like compounds. Cr, Ni, Cd, As, Pb, and V contents in wetland sediments significantly differ from sampling sites and depths, and varied in the following order: V > Cr > Ni > Pb > As > Cd. Principal component analysis showed that the distribution of heavy metals was primarily affected by urbanization and secondarily affected by other abiotic factors.

Study of marine noctilucence in marine is important to fishery, environmental monitoring and military affairs. A luminous bacterial strain D2 was isolated from the marine sediment samples collected near Donghai Island in Zhanjiang, China. The primary cultural and luminescent conditions of luminous bacterium D2 which was identified as Vibrio sp. were determined in liquid culture. The results showed that pH 7.0, 35 °C, with 2.0 % NaCl, were the best growth conditions, and pH5 - 6, 20 °C, OD600 0.08, with 3.0 % NaCl, were the optimal luminescent conditions. Published quorum sensing system