Ultrastructural Diversity And Function Of Extracellular Polymers From Marine Bacteria

The common extracellular appendages of bacteria are flagella,pili and extracellular polymers.Extracellular polymer is one of the most important extracellular structures of a bacteria.The main components of extracellular polymers are bacterial extracellular polysaccharides,and a small amount of proteins,small molecules and so on.Therefore,the composition of extracellular polymers is often referred to as saccharides.Extracellular polymers of bacteria play an important role in many aspects,such as bacterial resistance to drying environment and nutrient adsorption.To elucidate the composition,structure and function of bacterial extracellular polymers is a basic research in microbiology.Studies have shown that the proportion of bacteria producing extracellular polymers in marine bacteria is high,and the main components of extracellular polymers are usually heteropolysaccharides.The chemical structure diversity of heteropolysaccharides is also high.The extracellular polymers of marine bacteria are important materials for.studying the structure and function diversity of microbial extracellular polymers At the same time,elucidating the structure and function of extracellular polysaccharides from marine microbial species will also be helpful to understand the ocean organic carbon cycle.In the past,transmission electron microscopy(TEM)has been used to study the morphology and structure of bacterial extracellular polymers.However,TEM technology relies on suitable staining methods for heavy metals,which is not suitable for many kinds of bacterial extracellular polymers.Atomic force microscopy(AFM)is a high-resolution microscopic imaging technology.It does not need dyeing or vacuum conditions in operation.It can obtain high-resolution images of microbial structure at nanometer scale.AFM has great advantages in microbial research,and has been widely used to study bacterial extracellular attachment structures,such as bacterial bodies,cell walls,photosynthetic membranes,flagella and pili.However,up to now,the study on the structure of bacterial extracellular polymers by AFM has been extremely limited.In this thesis,we used marine and polar bacteria separated and preserved in our laboratory as research materials,studied the ultrastructure of bacterial extracellular polymers by AFM,and analyzed the ecological function of extracellular polysaccharides by experiments.We have obtained the following results:1.Ultrastructure of Extracellular Polymers from Marine BacteriaIn this paper,we selected 33 genera of bacteria from 4 phylums from the oceans and polar regions,and studied the ultrastructure of their extracellular appendages on nanoscale by AFM.The results showed that the sensitivity of atomic force microscopy to the detection of bacterial extracellular polymer structure is very high.The results showed that the extracellular polymers of marine bacteria have very high structural diversity,among which many ultrastructural structures have not been reported before.At the same time,the ultrastructure of extracellular polymers is different among different species of marine bacteria,even among the same species.2.Study on species abundance of marine bacteria producing extracellular polymers in different sea areasIn order to study the abundance of extracellular polymers produced by marine bacteria in specific marine sites,we first selected marine samples from Mariana Trench and the Arctic W2 site to study the culturable bacteria isolated from the samples.The results showed that there were 10 species of culturable marine bacteria in Mariana trench(9 species of Proteobacteria bacteria and 1 species of Bacteroides bacteria).Among them,5 species of bacteria(4 species of Proteobacteria bacteria and 1 species of Bacteroides bacteria)produced extracellular polymers.There are 4 kinds of culturable marine bacteria(2 kinds of Proteobacteria and 2 kinds of Bacteroides)isolated from the Arctic W2 site.All 4 kinds of bacteria produce extracellular polymers.Subsequently,we selected the surface waters of Antarctica and directly studied the natural bacteria in the seawater samples.The results showed that the proportion of extracellular polymers produced by marine bacteria was very high in the natural state,the ultrastructure of bacterial extracellular polymers was very various.3.Biological Functions of Extracellular Polysaccharides from Marine Bacteria Winogradskyella sp.4-5In order to study the biological functions of extracellular polymers of marine bacteria,we selected a marine strain Winogradskyella sp.4-5 isolated from Arctic(11°39'36.00"E,78°59'17.40"N),which produced a large amount of extracellular polymers.Previous studies have shown that the main component of its extracellular polymers is polysaccharides.Firstly,the results showed that the extracellular polysaccharides of the strain did not have significant effect on improving the salt tolerance of the strain itself.Secondly,the results showed that the exopolysaccharide produced by the strain had a certain antifreeze effect on the strain itself.The result indicated that EPS may protect strains in extreme environment and reduce the damage caused by repeated freezing and thawing.Finally,it was found that the extracellular polysaccharides of the strain had the function of adsorbing nutrients from the environment.After adsorbing organic matter particles from the environment,the ultrastructure of the extracellular polysaccharides of the strain would change significantly under the microscope.