Studies On Ferric Reducing Bacteria In Deep-sea Hydrothemal Fields And Their Fe-Reducing Mechanism

Hydrothermal field is a particular ecosystem on the earth.It contains massive novel microorganisms and unique genomic resources.Under the environment of deep-sea,bio-mineralization is a considerable factor contributing to the mine formation of Iron,Manganese and Sulfur.Dissimilation Iron Reducing Microorganism(DIRM)contributes to the distribution of iron and was considered as one of the most important geochemical process.The study of DIRM in hydrothermal fields is of great significance to explain the process of bio-mineralization and iron cycling.To study the characteristics and reducing mechanism of DIRM in hydrothermal fields,we carried out the research on the DIRM related to polymetallic sulfides from DeYin Hydrothermal Field on South Mid-Atlantic Ridge and Baidi Hydrothermal Field on South-West Indian RidgeWe obtained 157 iron reducing cultures from 23 hydrothermal samples.The cultures includs 5 of low-temperature,151 of high-temperature and 1 of room-temperature.Among them,14 cultures can grow steadily(up to 10 times of re-inoculation).The diversity of 6 fast-growing and well crystallizing cultures were analyzed by 16 S rRNA gene.In the culture of 224T6GL7-3,2 species were found,with the most relative genus Carboxydocella and Anaerobacter.In the other 5 cultures,only one species was found in each culture with the most relative genus Caloranaerobacter,Carboxydocella,Desulfotomaculum,Clostridium and Geoglobus,respectively.A novel strain DY30321 of DIRM isolated from South-West Indian Ridge was characterized and identified by polyphasic systematics.The strain reduces Hydrous Ferric Oxide(HFO)under room temperature.The wild range of growing pH(4.0?10.0)facilitates it to accomodate the complex hydrothermal environment.The strain was idendified as a novel genus of Clostridia,with the name Wukongibacter proposed.The type species is Wukongibacter baidiensis,and the type strain is DY30321T.This strain was gram positive stained,spore forming,and rod shaped.Its genomic G+C content is 33.4 mol%.No flagellum was observed.No respiratory quinone was detected.The polyphasic identification of the novel strain expands our knowledge of DIRM.The observation of iron reducing process is the basis of the study.The reduced products analysis is the primary assessment of their potential application.Long term observation was carried out to the iron reducing cultures and mineral crystals generated from these cultures were investigated.The reducing rate of the cultures differs greatly from each other.The shortst time required for iron reducing ranged from 3 days to 3 years.HFO was transformed to nano-sized crystals,which are mainly cubical or fusiform,with elements Fe and O as the main elements.Genome annotation was carried out to four ferric reducing culutres and the iron reducing mechanism mainly based on electron shuttle model was precdicted.Results showed that the system of Biogenesis of c-type cytochromes exists in Wukongibacter,Carboxydocella,Anaerobacter and Geoglobus;Complete flagellum system exists in the first three.Under the existence of electron shuttle(such as humic acids),electrons from DIRM cell were transported to ferric iron throught shuttles.When there is lack of electron shuttles,soluble cytochrome c was procuced as shuttles or flagella were synthesized to drive cells to the surface of ferric oxideA considerable number of DIRM were isolated from the samples of Atlantic Ocean and Indian Ocean.To a certain extent,the long time span of the iron reducing processes implies new type of ferric iron reduction.These nanoscale crystals transformed from HFO may have potential application in nanometer materials.DIRM are involved in the iron cycle in hydrothermal field,however their role under the nature environment needs to be studied through deep-sea simulation experiments.