A Preliminary Study On Biogeographic Distribution And Algae-associated Bacteria Of Two Species Of Green Tides Algae

Green tides are marine ecological phenomenon caused by the fulminant proliferation of macroalgae,which often have a serious impact on marine inshore ecosystems.In recent years,green tides caused by Ulva has become a prominent ecological disaster in coastal areas of China.Previous studies have shown that new species and new recorded species often lead to the outbreak of green tides,especially in China.In addition to the ability to adapt to the environment and physiological properties,the dispersal and invasive abilities of alien species may also be related to their associated algae-associated bacteria.Algae and algae-associated bacteria have close interactions,which play an important role in the growth and development of algae,and are even related to the outbreak of macroalgae.Because endophytic bacteria are relatively stable and specific,they can also be used as an effective tracer for species invasion.This study is mainly to study the algae-associated bacteria of two species of green tides algae.Firstly,through literature research and data analysis,the distribution characteristics,diffusion mechanism,geographic source and green tide risk of the newly recorded species are explored.Then,from the perspective of algae-bacteria interaction,the algae-associated bacteria of two species of green tides algae were isolated,cultured and identified.The composition and abundance of the obtained algae-associated bacteria were compared and analyzed by sequence comparison and phylogenetic analysis,and the function of the relevant strains was predicted through literature research.The main results are as follows:1)The biogeographic distribution characteristics of the new record species of U.californnica.The species of U.californnica was the first record on the coastline of mainland China.Combined with the results of molecular,morphological,and developmental processes,all of the samples were male gametophytes,and self-reproduced only through parthenogenesis.Because the southern and northern populations are genetically identical,we believe that U.californica was an alien species introduced to mainland China by a single population,and has rapidly spread throughout coastal China in an apparent discontinuous distribution pattern that requires close attention for its potential green bloom risk.2)Bacterial community composition of a new recorded species of U.californica.346 strains were isolated from 8 samples of U.californica,they belonged to 25 genera in3 phylum,proteobacteria were predominant.At the genus level,Alteromonas was dominant among the epiphytic bacteria,while Halalkalibacter was dominant among the endophytic bacteria.There were also significant differences in the composition of the strains isolated on different U.californica samples.3)Molecular identification of the green tide causative species of U.meridionalis and community composition of bacteria.In this study,we identified the species responsible for two green tides events in Dongshan and Shanwei,and both species were U.meridionalis.A total of 136 strains were isolated from 2 green tides samples and 1attached sample,belonged to 9 genera in 3 phylum,and firmicutes were dominant.Halalkalibacter was dominant in both epi-and endo-bacteria.There were significant differences in the community structure between the attached samples and the green tides samples.For example,Alteromonas was unique to the attached samples,and the community structure of the two floating samples is also very different,but all the green tides samples and the attached samples have a common genus-Halalkalibacter.4)Functional prediction of isolated strains.As the dominant endophyte bacteria of U.californica and U.meridionalis,respectively,Halalkalibacter nanhaiisediminis may play an important role in algal host resistance to environmental stress and in algal host growth.Unique species isolated from different U.meridionalis green tide samples may also have played a key role in algal blooms.This study provides an update on the biogeographic distribution of U.californica,a newly recorded species along the mainland of China,and provides a basis for assessing the risk of biological invasion and green tide.We first reveal the composition of a newly recorded species,U.californica and U.meridionalis,and predict their functions.These studies may provide a new clue for the origin and dispersal of Ulva species,as well as the outbreak mechanism,and also provide rich species resources for the construction of an algae-bacteria interaction test system.