SUMMARYMore than 700 bacterial species have been detected in human oral cavity. They form highly organized microbial communities and are responsible for many oral infectious diseases, such as dental caries and periodontal disease. The prevention and treatment of these diseases require a comprehensive knowledge of oral microbial communities, which largely relies on culturedependent methods to have detailed phenotypic and physiological analysis of these communities. However, most of the currently available lab media can only selectively support the growth of a limited number of bacterial species within these communities, and fail to sustain the original oral microbial diversity. In this study, using denaturing gradient gel electrophoresis (DGGE) as an index to systematically survey and analyze the selectivity of commonly used lab media, we developed a new medium (SHI medium) by combining the ingredients of several selected media which can support different sub-populations within the original oral microbial community derived from pooled saliva. DGGE and 454 pyrosequencing analysis showed that SHI medium was capable of supporting a more diversified community with a microbial profile closest to that of the original oral microbiota. Furthermore, 454 pyrosequencing revealed that SHI medium supported the growth of many oral species that have not been cultured so far. Crystal violet assay and the CLSM (confocal laser scanning microscope) analysis indicated that, compared with other media, SHI medium is able to support more complex saliva-derived biofilm with higher biomass yield and more diversified species. This DGGE-guided method could also be used to develop novel media for other complex microbial communities.

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Coarse-grained simulations are adopted to study the adsorption behavior of lysozyme on different (hydrophobic, neutral hydrophilic, zwitterionic, negatively charged, and positively charged) surfaces at the mesoscopic microsecond time scale (1.2 μs). Simulation results indicate the following: (i) the conformation change of lysozyme on the hydrophobic surface is bigger than any other studied surfaces; (ii) the active sites of lysozyme are faced to the hydrophobic surface with a "top end-on" orientation, while they are exposed to the liquid phase on the hydrophilic surface with a "back-on" orientation; (iii) the neutral hydrophilic surface can induce the adsorption of lysozyme, while the nonspecific protein adsorption can be resisted by the zwitterionic surface; (iv) when the solution ionic strength is low, lysozyme can anchor on the negatively charged surface easily but cannot adsorb on the positively charged surface; (v) when the solution ionic strength is high, the positively charged lysozyme can also adsorb on the like-charged surface; (vi) the major positive potential center of lysozyme, especially the residue ARG128, plays a vital role in leading the adsorption of lysozyme on charged surfaces; (vii) when the ionic strength is high, a counterion layer is formed above the positively charged surface, which is the key factor why lysozyme can adsorb on a like-charged surface. The coarse-grained method based on the MARTINI force field for proteins and the BMW water model could provide an efficient way to understand protein interfacial adsorption behavior at a greater length scale and time scale.

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Phenolic compounds have been implicated as autotoxins of cucumber under mono‐cropping management systems. Inhibition of cucumber growth may result from direct uptake of phenolic compounds or an indirect effect resulting from changes in soil microflora. In the present study we monitored the dynamics of soil phenolics in a continuously mono‐cropped cucumber system and then assessed the effects of these compounds on soil microbial communities. Six phenolic compounds were identified in all soil samples in the continuously mono‐cropping system. Soil total phenolic content increased extensively in the first cropping, but maintained a relatively stable level in the following croppings. Amendments of phenolics at the concentration detected in the soil showed inhibitory effects on cucumber seedling growth and stimulatory effects on soil dehydrogenase activity, soil microbial biomass carbon content and soil bacteria and fungi community sizes. Amendments of phenolics caused shifts in soil microbial community structures and soil bacteria and fungi communities had different responses. Our results suggested that direct phytotoxic effects of phenolics on cucumber probably did not happen in continuous mono‐cropping systems, but they might indirectly influence cucumber performance by changing soil microbial communities.