Controlled expression of lysis gene E by a mutant of the promoter pL of the thermo-inducible λcI857-pL system

AIMS

To identify a lambda promoter pL mutant that could extend the thermal stability of the thermo-inducible λcI857-pR/pL system and to evaluate the effects of the modified system for the controlled expression of lysis gene E during the production of bacterial ghosts (BGs).

METHODS AND RESULTS

The promoter pL mutant was identified by random mutagenesis and site-directed mutagenesis. The results showed that a T → 35C mutation in the pL promoter was responsible for the phenotype alteration. Under the same induction conditions, the lysis rates of the modified lytic system on Escherichia coli and Salmonella enteritidis were significantly lower than that of the control, while the lysis rates of Escherichia coli with the thermo-inducible lytic system were significantly higher than that of S. enteritidis with the corresponding plasmid (P < 0·05).

CONCLUSIONS

Increasing the heat stability of the thermo-inducible lytic systems decreased lysis efficiency during the production of BGs. There exist differences in the lysis efficiency of thermo-inducible lytic systems between different bacterial strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings enrich current knowledge about modifications to thermo-inducible systems and provide a reference for the application of these modified systems for the production of BGs and controlled gene expression in bacteria.

Prokaryotic expression and immunoassay of grass carp reovirus capsid VP6 protein

Grass carp reovirus (GCRV) of the genus Aquareovirus and the family Reoviridae causes a severe hemorrhagic disease in grass carp fingerlings in China. GCRV genome is composed of 11 double-stranded RNA segments, of which segment 8 encodes the major core capsid protein VP6. In this study, the VP6 gene following an RT-PCR-amplification from the GCRV 104 strain was cloned into an expression vector pET-32a to obtain pET-32(a)-VP6. The VP6 protein was expressed in Escherichia coli BL21 as a fusion protein of 64 kDa. After purification with the HisLink Spin Protein Purification System the VP6 protein was used to raise a specific polyclonal antibody in Balb/c mice. Presence of VP6 protein was proved in bacterial lysates containing VP6 fusion protein by Western blot analysis and in GCRV-infected CIK cells by immunofluorescent staining using polyclonal antibody. These results may be helpful in further studies of interactions between GCRV and cells and in preparation of an engineered vaccine against GCRV.

Supplemental diagnosis of a myxozoan parasite from common carp Cyprinus carpio: synonymy of Thelohanellus xinyangensis with Thelohanellus kitauei

Thelohanellus kitauei Egusa et Nakajima, 1981, was described from common carp Cyprinus carpio L. in Japan. In China, a myxosporean infecting the intestinal tissue of the same host species was described as Thelohanellus xinyangensis Xie, Gong, Xiao, Guo, Li et Guo, 2000, despite many similarities to T. kitauei. To examine the potential conspecificity of these species, a morphological and molecular investigation of T. xinyangensis was conducted. Comparing myxospore morphology, the mean spore length and width of each species is not identical between species, but ranges of dimensions overlap. These data are more suggestive of intraspecific variation than distinct species. Comparison of relative ratios of spore length to polar capsule length and spore width to polar capsule width of T. xinyangensis and T. kitauei reveal no differences and scanning electron microscopy reveals a smooth spore surface of T. xinyangensis, which is consistent with that of T. kitauei. Most convincingly, DNA sequences of the small subunit ribosomal RNA (ssrRNA) gene of the two species were identical. From the morphological and molecular biological data, we propose T. xinyangensis from the intestine of common carp is not a distinct species and is synonymous with T. kitauei.