Study Of The Algicidal Mechanism On Skeletonema Costatum By Halobacillus Bacteria

Harmful algae blooms(HABs)are a global ecological disaster and its biological control has been a hotspot in the HAB research field.In recent years,a large number of marine algicidal bacteria have been isolated and identified,and much effort has been devoted to the algicidal effect.However,knowledge about its algicidal mechanism is still limitedPreviously,a strain of Halobacillus sp.HSQAY1 was isolated from HABs area in Mirs Bay and the culture supernatant of the strain was found to have strong algicidal effect on S.costatum.However,little is known about the mechanism behind the algicidal process.This study applied the proteomic approach together with the physiological study to investigate the variations of S.costatum cell from morphology,physiology and proteomics when treated with the HSQAY1 supernatant,identified and screened differentially displayed proteins,characterized proteins and biological processes affected by HSQAY1 supernatant,and discussed the mechanism of Halobacillus sp.HSQAY1 against S.costatum.The main results were as follows:(1)Cell morphology were observed and measured by light microscopy.Results showed that the algicidal effect occurred after 12-h-treatment and the cell chains of S.costatum broke into individual cells when treated with the HSQAY1 supernatant.At the same time,the algicidal substances inhibited cell division and thus cell length increased significantly.After that,the cell protoplast formed a vesicle at the end of the cell and finally inflated to rupture.(2)After HSQAY1 supernatant treatment,the contents of protein,chlorophyll a(Chla)and nitrogen,Fv/Fm,Y(II),the activities of nitrate reductase,nitrite reductase and glutamine synthetase decreased significantly.However,the contents of malondialdehyde,the activities of superoxide dismutase and peroxidase increased significantly.The up-taking and utilization of nitrogen were inhibited in S.costatum by algicidal substances,which affected the biosynthesis of proteins,photosynthetic pigments and eventually inhibited the cellular proliferation and division.Besides,the increase of reactive oxygen species content may alter the cell membrane permeability and result in the cell inflation and rupture.(3)Proteomic study showed that 4,600 proteins were identified from S.costatum,82 of them were differentially displayed in the 12-h-treatment: 56 up-regulated and 26 down-regulated,437 proteins were differentially displayed in the 24-h-treatment: 268 up-regulated and 169 down-regulated.Under the treatment of HSQAY1 supernatant,proteins involved in protein degradation and cell apoptosis were significantly up-regulated,while proteins participated in nitrogen metabolism,photosynthetic pigments metabolism,photosynthesis,protein translation and cell cycle regulation were significantly down-regulated.The differential expressions of these biological processes further indicate that the inhibition of nitrogen absorption and utilization is the primary reason for the algicidal effect.