Selection Of The Siderophore-producing Bacterial Strain And Effects On The Growth Of Cyanobacteria

In this experiment, effects between microbial siderophores and cyanobacterias infresh water system had been studied. Most of laboratories had pay attention to theproperties of the bacteria and the production number of siderophore，but the relationshipbetween them had not been found。Stenotrophomonas Maltophilia had been selected，foroptimizing the culture medium and growth factors。Prepare the siderophore to study itseffects on M. aeruginosa and A. flos-anabaena，to provide methods and the direction tosolve the problem of pollution.In this study, total of28bacterial strains,isolated from Donghu Lake and YangtzeRiver,were screened for their ability to produce siderophore by using an improveduniversa1Chmme Azuml S（CAS）-agar plate method. Based on the conventional microbialidentification and16SrDNA sequence,the bacterial strains6#,15#,J9#which was found toproduce high level of the siderophore were identified as Pseudomonas,StenotrophomonasMaltophilia,Proteobacteria. Before that, the sequence of gene of the bacterial strain15#was analyzed and the phylogenetic tree was constructed.The orthogonal experiment test method was used by optimizing the culture mediumand growth factors for the highest siderophore yield by the strain15#.The optimal mediumcomponents were NaNO₃0.4%（w/v）,sucrose3.0%（w/v）,10mM L-glutamic acid, K₂HPO₄0.3%（w/v）,MgSO₄0.008%（w/v）；and the optimal growth factors were shaking at thespeed of1200rpm and the temperature of28℃. After120h of cultivation, the siderophoreproduction can reach88.7ug/ml.The crude siderophore from the culture supernatants of the siderophore-producingbacterial strain Stenotrophomonas Maltophilia15was extracted with macroporous resin.After that, the solution was dried at low temperature to remove the extraction solvent. Thedry powder of the siderophore was dissolved in deionized water to obtain the stocksolution of the siderophores （120/ml）. Different volume of the stock solution of thesiderophores was added to the culture of M. aeruginosa FACHB-905and A. flos-anabaenaFACHB-245, the growth indexes including the cell density （OD680）, the cell number of the growth rate, the concentration of Chlorophyll a, carotenoids, total soluble proteins,phycocyanin and microcystin were detected. According to the data obtained,we found thataddition of siderophore have a negative impact on the growth of cyanobacteria samples, thedecline of the cell density （OD680） and the cell number of the growth rate show that thegrowth rate of the cyanobacteriasampls were suppressed. In the experimental stage,cyanobacteriasampls of FACHB-905experimental group1,2,3were66.18%,77.27%,FACHB-245experimental group1,2,3were66.18%,77.27%,82.32%of the controlgroup. At the same time, the chelation of siderophore inhibit absorption of Fe³⁺forcyanobacteria, affect synthesis of chlorophyll and protein so that the cyanobacteria die,inhibit the production of cyanotoxins in M. aeruginosa. Microcystin of FACHB-905experimental group1,2,3were28.54%,41.59%,50.73%of the control group. The resultshow that siderophores of high-yielding siderophore bacteria could be used as an effectivemeans for controlling cyanobacterial overgrowth such as M. aeruginosa and A.flos-anabaena in eutrophic waterbodies.