RESUMO
Many types of Bacillus thuringiensis (Bt)-crops are being grown worldwide, triggering concerns about their potential impact on humans and livestock. To ensure better yield and food safety in China, an attempt has been made to develop Bt-rice targeting a broad range of insects. We aimed to investigate whether feeding genetically modified rice expressing the Bt chimeric Cry1Ac/Cry1Ab protein has any effects on the intestinal microbiota of broilers. Broilers were fed either Bt-rice or its unmodified isogenic parent line for 42 days, and total DNA was isolated from cecum contents for high-throughput sequencing of the 16S rRNA gene. In total, 1,241,005 reads, assigned to 12 phyla, 31 families, and 48 genera were generated. No significant differences were observed in the relative abundance of organisms identified among the major phyla, families, and genera, except for two less abundant families, Thermoanaerobacteraceae and Peptostreptococcaceae, and two less abundant genera, Anaerotruncus and Gelria. The results were in agreement with those from culture-based analysis and Biolog EcoPlates. These results illustrate that feeding Bt-rice has no adverse effects on the broiler intestinal microbiota and provide sufficient support for the food safety of Bt-rice.
RESUMO
OBJECTIVE: The purpose of this study was to characterize sigL mutant in Bacillus thuringiensis (Bt) HD-73, and to determine the function of sigL gene of Bt. METHODS: We studied the growth speed of the sigL mutant and complementary strain in different nutrient medium with different amino acids as nitrogen source respectively. lacZ gene was fused with the promoter of the acoR gene and bkdR gene, and two recombined genes were expressed in sigL mutant strain and HD-73 wild strain sequentially. RESULTS: sigL mutant could not grow on arginine, proline, valine, isoleucine, glutamine, phenylalanine, methionine and tryptophane as the sole nitrogen source separately. Activity of beta-galactosidase in sigL mutant strain was much lower than it in wild-type strain and sequence analysis showed that the domain of AcoR and BkdR are similar to the conserved domain of SigL-dependent transcriptional activator in Bt. CONCLUSION: The deletion of sigL gene maybe blocked some important metabolic pathways. AcoR and BkdR are sigma L-dependent transcriptional activators in Bacillus thuringiensis strains, probably the operons which were regulated by AcoR and BkdR were also controlled by sigma L respectively.
Assuntos
Bacillus thuringiensis/genética , Bacillus thuringiensis/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Mutação , Fator sigma/genética , Aminoácidos/metabolismo , Bacillus thuringiensis/crescimento & desenvolvimento , Regulação Bacteriana da Expressão Gênica , Fator sigma/metabolismo , Transativadores/genética , Transativadores/metabolismo , Transcrição GênicaRESUMO
To indicate the relationship between structure and function of loops from Bacillus thuringiensis insecticidal crystal protein Cry1Ba, and the influence of amino acids mutation on toxicity against diamond back moth Plutella xylostella, five mutations at the loops of Cry1Ba were constructed by overlapping primer PCR, and expressed in E. coli BL21 (DE3). Bioassay results showed that the toxicity of mutation M1 (loop1: 340WSNTR344-deletion), compared with that of Cry1Ba (LC50 0.96 microg/mL), decreased significantly with LC50 35.51 microg/mL. And the toxicity of mutation M2 (402Y-G), M3 (400GIYLEP405-PSAV), M4 (400GIYLEPIH407-ILGS) was also reduced to some extent respectively. Only M5 (mutation at loop3: 472LQSRV476 - AGAVYTL) showed slightly increased activity against P. xylostella, but not significantly (LC50 0.81 microg/mL). Referring to the structures of Cry1Ba which was predicted using Swiss-Model software, and bioassay data, we can conclude that loop1 and loop2 play a important role on determining the activity of Cry1Ba against P. xylostella.
Assuntos
Animais , Bacillus thuringiensis , Genética , Metabolismo , Proteínas de Bactérias , Química , Genética , Endotoxinas , Química , Genética , Escherichia coli , Genética , Metabolismo , Proteínas Hemolisinas , Química , Genética , Modelos Moleculares , Mariposas , Microbiologia , Mutação , Estrutura Secundária de Proteína , Relação Estrutura-AtividadeRESUMO
The complete nucleotide sequence of a large (67kb) cryptic plasmid pBMB67 from Bacillus thuringiensis strain YBT-1520 was determined. Of the 74 predicted open reading frames (ORFs), 25 (34%) were assigned putative functions, 18 (24%) encoded conserved hypothetical proteins, and 31 (42%) had no homology to any genes present in the current open databases. The ORFs with similar functions were organized in a modular structure; thus, the DNA sequence of pBMB67 could be functionally divided into three modules, including a 39kb transfer region encoding homologs of the Agrobacterium tumefaciens VirB/D4 system components VirB1, VirB4, VirB11, and VirD4, as well as homologs of Gram-positive conjugation proteins. We also found a potential operon that was analogous to the Rap-Phr cassettes from Bacillus subtilis, which are involved in cell-cell communication and transcriptional regulation. Thus, we suggest that pBMB67 is likely to be implicated in cell-cell signaling and plays a role in the regulation of several cellular processes, with the production of exoprotease being one of the candidates.
