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Abstract. The modern instrumental record is analyzed in an attempt to reveal the dynamical structure and origins of the major modes of interannual variability of East Asian summer monsoon (EASM) and to elucidate their fundamental differences with the major modes of seasonal variability. These differences are instrumental in understanding of the forced (say orbital) and internal (say interannual) modes of variability in EASM. We show that the leading mode of interannual variation, which accounts for about 39% of the total variance, is primarily associated with decaying phases of major El Nino, whereas the second mode, which accounts for 11.3% of the total variance, is associated with the developing phase of El Nino/La Nina. The EASM responds to ENSO in a nonlinear fashion with regard to the developing and decay phases of El Nino. The two modes are determined by El Nino/La Nina forcing and monsoon-warm ocean interaction, or essentially driven by internal feedback processes within the coupled climate system. For this internal mode, the intertropical convergence zone (ITCZ) and subtropical EASM precipitations exhibit an out-of-phase variations; further, the Meiyu in Yangtze River Valley is also out-of-phase with the precipitation in the central North China.In contrast, the annual cycle forced by the solar radiation shows an in-phase variation between the ITCZ and the subtropical EASM precipitation. Further, the seasonal march of precipitation displays a continental-scale northward advance of a southwest-northeastward tilted rainband from mid-May toward the end of July. This coherent seasonal advance between Indian and East Asian monsoons suggests that the position of the northern edge of the summer monsoon over the Correspondence to: J. Liu (jianliu@niglas.ac.cn) central North China may be an adequate measure of the monsoon intensity for the forced mode. Given the fact that the annual modes share the similar external forcing with orbital variability, the difference between the annual cycle and interannual variation may help to understand the differences in the EASM variability on the orbital time scale and in the modern records.

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Aims: The aim of this study was to investigate functions of flagellar genes fliC2, fliC12, fliA and flhDC in a bacterial fish pathogen Edwardsiella tarda. Methods and Results: In this study, functions of flagellar genes, fliC2, fliC12 (fliC1 + fliC2), fliA and flhDC (flhD + flhC) of Edw. tarda H1 were analysed by constructing in-frame deletion mutants respectively and complementary strains fliC2 + and fliA + . Electron microscopy revealed that in-frame deletion of fliC12, fliA and flhDC significantly impaired the number and length of flagellar filaments, resulting in loss of both swimming and swarming motilities of the bacteria. In addition, compared to the wild-type strain and complementary strains, the flagellum-impaired mutants exhibited reduced biofilm formation ability, showed decreased ability in adherence and internalization to Epithelioma papulosum cyprini (EPC) cells and reduced pathogenicity to zebrafish. Conclusions: These results indicated that fliC12, fliA and flhDC of Edw. tarda played essential roles in flagellar filaments structure, bacteria motility, biofilm formation, adherence, internalization and pathogenicity of this bacterium. Significance and Impact of the Study: This study revealed that flagella function in facilitating virulence and it may provide a new target for vaccines against Edw. tarda infection.

Aims: The aim of this study was to investigate the role of invasin in a bacterial fish pathogen Edwardsiella tarda. Methods and Results: In this study, an in-frame deletion mutant of invasin (Dinv) in Edw. tarda H1 was constructed through double crossover allelic exchange to explore the function of invasin in virulence to fish. Meanwhile, an invasin overexpression strain (inv + ) was obtained by electrotransformation of a low-copy plasmid pACYC184 carrying the intact invasin into the Dinv mutant. Several virulence-associated characters of the mutants and wild-type strain were tested. Compared with the wild-type H1, haemolytic activity and biofilm formation were decreased in Dinv, while increased significantly in inv + . In addition, the invasin overexpressing strain inv + exhibited increased internalization into Epithelioma Papulosum Cyprini (EPC) cells. Moreover, in zebrafish model, Dinv showed decreased virulence compared with H1, while inv + restored the virulence of wild type completely. Conclusions:The results demonstrated that invasin of Edw. tarda plays essential roles in haemolytic activity, biofilm formation, adherence, internalization and pathogenicity of this bacterium. Significance and Impact of the Study: This study revealed the role of invasin in Edw. tarda infection and provided useful information for further unveiling the pathogenesis of Edw. tarda.

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