Effects of 90-Day Feeding of Transgenic Maize BT799 on the Reproductive System in Male Wistar Rats.

BT799 is a genetically modified (GM) maize plant that expresses the Cry1Ac gene from Bacillus thuringiensis (Bt). The Cry1Ac gene was introduced into maize line Zhen58 to encode the Bt crystal protein and thus produce insect-resistant maize BT799. Expression of Bt protein in planta confers resistance to Lepidopteran pests and corn rootworms. The present study was designed to investigate any potential effects of BT799 on the reproductive system of male rats and evaluate the nutritional value of diets containing BT799 maize grain in a 90-day subchronic rodent feeding study. Male Wistar rats were fed with diets containing BT799 maize flours or made from its near isogenic control (Zhen58) at a concentration of 84.7%, nutritionally equal to the standard AIN-93G diet. Another blank control group of male rats were treated with commercial AIN-93G diet. No significant differences in body weight, hematology and serum chemistry results were observed between rats fed with the diets containing transgenic BT799, Zhen58 and the control in this 13-week feeding study. Results of serum hormone levels, sperm parameters and relative organ/body weights indicated no treatment-related side effects on the reproductive system of male rats. In addition, no diet-related changes were found in necropsy and histopathology examinations. Based on results of the current study, we did not find any differences in the parameters tested in our study of the reproductive system of male rats between BT799 and Zhen58 or the control.

PrfA led to reduced biofilm formation and contributed to altered gene expression patterns in biofilm-forming Listeria monocytogenes.

The foodborne pathogen Listeria monocytogenes has the ability to develop biofilm in the food-processing environment, which becomes a major concern for food safety. PrfA, a key transcriptional activator that regulates most of the known listerial virulence gene expression, has been shown to promote L. monocytogenes biofilm formation. In this study, the whole-genome microarray was used to identify differentially expressed genes associated with the putative interaction between biofilm formation and PrfA in L. monocytogenes. Comparative transcriptome analyses indicated that over 21.9 % of the L. monocytogenes EGDe genes (627 out of 2,857 predicted) were altered in their expression of biofilm compared to the planktonic phase. These genes were classified into different functional categories which cover most of the biochemical functions encountered in bacterial cells, indicating that L. monocytogenes biofilm formation is probably controlled by a complex regulation network involved in variable genes required for the different biological pathways. Further comparison of gene expression profiles of biofilms between L. monocytogenes EGDe and its PrfA deletion mutant revealed 185 genes associated with PrfA and biofilm formation. Except for 10 genes, transcription levels of 175 genes were completely opposite between ΔprfA and wild-type during the biofilm formation, i.e., up-regulated genes in ΔprfA were down-regulated in the wild-type strain, and vice versa, indicating that loss of PrfA dramatically altered gene expression patterns in L. monocytogenes biofilm and resulted in reduced ability of the biofilm formation.

Carbon catabolite control is important for Listeria monocytogenes biofilm formation in response to nutrient availability.

The foodborne pathogen Listeria monocytogenes has the ability to develop biofilm in food-processing environment, which becomes a major concern for the food safety. The biofilm formation is strongly influenced by the availability of nutrients and environmental conditions, and particularly enhanced in poor minimal essential medium (MEM) containing glucose rather than in rich brain heart infusion (BHI) broth. To gain better insight into the conserved protein expression profile in these biofilms, the proteomes from biofilm- and planktonic-grown cells from MEM with 50 mM glucose or BHI were compared using two-dimensional polyacrylamide gel electrophoresis followed by MALDI-TOF/TOF analysis. 47 proteins were successfully identified to be either up (19 proteins) or down (28 proteins) regulated in the biofilm states. Most (30 proteins) of them were assigned to the metabolism functional category in cluster of orthologous groups of proteins. Among them, up-regulated proteins were mainly associated with the pentose phosphate pathway and glycolysis, whereas a key enzyme CitC involved in tricarboxylic acid cycle was down-regulated in biofilms compared to the planktonic states. These data implicate the importance of carbon catabolite control for L. monocytogenes biofilm formation in response to nutrient availability.

SigB-dependent tolerance to protein synthesis-inhibiting antibiotics in Listeria monocytogenes EGDe.

The alternative sigma factor SigB in food-borne pathogen Listeria monocytogenes was determined in this study to be required for tolerance to protein synthesis-inhibiting antibiotics. The minimum inhibitory concentrations of tetracycline HCl and gentamicin sulphate against EGDeΔsigB were two- and fourfold less than those for EGDe, respectively. The ability of EGDeΔsigB to overcome the growth arrest caused by erythromycin and rifampin was also weaker than that of EGDe. The transcription analysis of four genetic loci (known to be induced by rifampin in Bacillus subtili) kat, fri, ropB and rsbU in EGDe and EGDeΔsigB in the absence or presence of rifampin revealed that: (1) expression of kat and fri genes is σ (B) dependent, but only the former is inducible by rifampin stress; (2) the transcriptional level of rpoB gene was stable under all the experimental conditions, while that of rsbU in EGDeΔsigB was remarkably higher in the absence of rifampin and significantly increased in EGDe but reduced in EGDeΔsigB after rifampin application, when compared to those in EGDe and EGDeΔsigB control without antibiotic, respectively. These results suggest that complex physiological reactions to tolerance of the antibiotic stress are variably regulated in bacteria, and in contrast to B. subtilis, rsbU in EGDeΔsigB may compensate for the σ (B)-dependent genes that are necessary for tolerance to rifampin stress and therefore plays a role in overcoming the antibiotic-triggered growth arrest.