在自然条件下，细菌能够形成高度结构化和群落化的生物膜结构，胞外DNA（eDNA）在这一过程中起到了重要作用。但是，仍然还有许多关键科学问题没有解决。我们首次证明了粘细菌的代表类群黄色粘球菌（Myxococcus xanthus）形成的生物膜胞外基质中存在大量高度组织化的eDNA，并提出eDNA与胞外多糖（EPS）发生了复杂的大分子相互作用。这一相互关系导致了eDNA以一种化学/物理有序的方式与EPS紧密交织，遵循类似的构建和分布模式，形成复合型胞外基质的网络结构。本项目将综合利用微生物学、生物化学、生物物理学和分子生物学等多种方法，从不同角度、多层面地研究M. xanthus胞外基质中eDNA与EPS相互作用的物化机制及其所赋予生物膜的重要生理功能，试图探求复合型胞外基质的构建原理。这将扩展对于eDNA和EPS在生物膜中履行功能的认知，有助于了解生物膜形成过程中所涉及的特殊分子机制。

Bacteria in natural surroundings are able to grow as biofilms, which comprises highly structured matrix-enclosed communities and differs profoundly from their planktonic counterparts at least in terms of physiological responses and developmental dynamics. This multicellular and polymer-encased mode of growth is now accepted as a preferred lifestyle option for prokaryotes. The extracellular matrix (ECM) is considered as the physical base of biofilm integration and structure-forming, which is defined as a mixture of extracellular polysaccharides (EPS), nucleic acids, proteins and other cell-released components. It has been noticed that some bacteria can produce substantial quantities of DNA to the ECM, which might be involved in biofilm formation. While little is known about present state of extracellular DNA (eDNA) in the biofilms, especially about its interactions with other macromolecules in the matrix and participation in the establishment of biofilm architecture. According to our preliminary studies, for the first time, it was recognized that all EPS-based biofilms formed by Myxococcus xanthus contained extensive amounts of eDNA molecules as part of the ECM. Most intriguingly, unlike the eDNA reported to be present in other bacteria that release free DNA into their environment, the eDNA in M. xanthus is intimately interwoven with the fibrillar EPS network and follows the same structural pattern. Based on further data presented in this application, it is indicated that DNA excretion in M. xanthus might be an active and coordinated event, which strengthens the EPS mechanical properties. Therefore, we developed the following working hypothesis: "In addition to be released by cell lysis associated with program cell death, M. xanthus cells may actively secrete eDNA in an organized fashion to bind EPS to build a stronger extracellular matrix network for improved biological activities". The study starts form elucidating the molecular and biochemical basis of interaction between eDNA and EPS, and their roles in establishment of a 'super' complex ECM. Subsequently, the biological features associated with the integrated DNA-EPS ECM will be analyzed. Moreover, the molecular components involved in actively producing eDNA and building the integrated ECM will be identified and characterized. The aims proposed in this application are designed to test our hypothesis which has the potential to provide insightful information on the role of ECM in biofilm formation as well as assign novel and important biological function to DNA beyond its role as genetic material. Furthermore, since eDNA and EPS do exist in various other pathogens, the finding derived from this study may help to further elucidate key virulence factors during biofilm formation, tissue adherence and invasion for these bacteria.