Shifeng Wang

The Pacific white shrimp Litopenaeus vannamei is the most important crustacean species in aquaculture, accounting for 70% of the total shrimp production in the world. In the past decade, development of the shrimp industry has been greatly impeded by disease prevalence, poor growth in low salinity inland water, dietary use of plant ingredients, and antibiotic overuse. The animal gut is a vital organ, and most of the gut functions, such as the functions of immunity, health regulation and nutrient absorption, are achieved by bacterial metabolism in the gut. Therefore, understanding the role of the gut microbiota of L. vannamei is important for improving the performance and production of L. vannamei in aquaculture. This paper summarizes the recent advancements in research on the composition of the gut microbiota of L. vannamei, the factors that influence the microbiota, and nutritional manipulation of the gut microbiota. In addition, based on the review, current problems are raised and future studies directed at solving these problems are proposed. Proteobacteria is the core bacterial group found the gut of L. vannamei, but other groups of bacteria can also be beneficial to shrimp health and growth. The abundance of opportunistic pathogenic bacteria in the gut can change with the developmental stage of the shrimp, diet composition, environmental factors, and in the presence of ambient toxicants such as sulfide. Various prebiotics, probiotics isolated from the gut of L. vannamei and other crustacean species, synbiotics and some organic acids have been used as dietary supplements to evaluate the health of L. vannamei farms. These additives have been compared for their roles in regulating shrimp growth and immunity and in shaping the community structure of the gut microbiota. Future studies should focus on understanding the underlying mechanisms between shrimp metabolism and the gut microbiota and on practical applications of dietary additives to solve problems faced by the shrimp industry.

Recombinant bacterial vaccines must be fully attenuated for animal or human hosts to avoid inducing disease symptoms while exhibiting a high degree of immunogenicity. Unfortunately, many well-studied means for attenuating Salmonella render strains more susceptible to host defense stresses encountered following oral vaccination than wild-type virulent strains and/or impair their ability to effectively colonize the gut-associated and internal lymphoid tissues. This thus impairs the ability of recombinant vaccines to serve as factories to produce recombinant antigens to induce the desired protective immunity. To address these problems, we designed strains that display features of wild-type virulent strains of Salmonella at the time of immunization to enable strains first to effectively colonize lymphoid tissues and then to exhibit a regulated delayed attenuation in vivo to preclude inducing disease symptoms. We recently described one means to achieve this based on a reversible smooth-rough synthesis of lipopolysaccharide O antigen. We report here a second means to achieve regulated delayed attenuation in vivo that is based on the substitution of a tightly regulated araC P(BAD) cassette for the promoters of the fur, crp, phoPQ, and rpoS genes such that expression of these genes is dependent on arabinose provided during growth. Thus, following colonization of lymphoid tissues, the Fur, Crp, PhoPQ, and/or RpoS proteins cease to be synthesized due to the absence of arabinose such that attenuation is gradually manifest in vivo to preclude induction of diseases symptoms. Means for achieving regulated delayed attenuation can be combined with other mutations, which together may yield safe efficacious recombinant attenuated Salmonella vaccines.

Abstract Polypropylene (PP)/carbon composites were prepared via melt blending PP with carbon fillers, including multiwalled carbon nanotubes (MWNTs) and carbon black (CB). Field‐emission scanning electron microscopy was used to research the morphology and dispersion of fillers in the PP matrix. The electrical properties, mechanical properties, and crystallization behaviors of PP/carbon composites were also investigated. The results show that the influence of MWNTs on the properties of PP composites is different with CB, which can be ascribed to the structure and aspect ratio difference between MWNTs and CB. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4823–4830, 2006

Increasing the immunogenicity to delivered antigens by recombinant attenuated Salmonella vaccines (RASV) has been the subject of intensive study. With this goal in mind, we have designed and constructed a new generation of RASV that exhibit regulated delayed attenuation. These vaccine strains are phenotypically wild type at the time of immunization and become attenuated after colonization of host tissues. The vaccine strains are grown under conditions that allow expression of genes required for optimal invasion and colonization of host tissues. Once established in the host, these virulence genes are turned off, fully attenuating the vaccine strain. In this study, we compared 2 of our newly developed regulated delayed attenuation Salmonella enterica serovar Typhimurium strains chi9088 and chi9558 with the Deltacya Deltacrp Deltaasd strain chi8133, for their abilities to express and present a secreted form of the alpha-helical region of pneumococcal surface protein A (PspA) to the mouse immune system. All 3 strains induced high levels of serum antibodies specific for PspA as well as to Salmonella antigens in orally immunized mice. However, both RASVs expressing delayed attenuation elicited significantly greater anti-PspA immune responses, including serum IgG and T cell secretion of IL-4 and IFN-gamma, than other groups. Also, vaccination with delayed attenuation strains resulted in a greater degree of protection against Streptococcus pneumoniae challenge than in mice vaccinated with chi8133 (71-86% vs. 21% survival, P </= 0.006). Together, the results demonstrate that the regulated attenuation strategy results in highly immunogenic antigen delivery vectors for oral vaccination.