A single amino acid mutation in an ABC transporter gene causes resistance to Bt toxin Cry1Ab in the silkworm, \u3cem\u3eBombyx mori\u3c/em\u3e

Bt toxins derived from the arthropod bacterial pathogen Bacillus thuringiensis are widely used for insect control as insecticides or in transgenic crops. Bt resistance has been found in field populations of several lepidopteran pests and in laboratory strains selected with Bt toxin. Widespread planting of crops expressing Bt toxins has raised concerns about the potential increase of resistance mutations in targeted insects. By using Bombyx mori as a model, we identified a candidate gene for a recessive form of resistance to Cry1Ab toxin on chromosome 15 by positional cloning. BGIBMGA007792-93, which encodes an ATP-binding cassette transporter similar to human multidrug resistance protein 4 and orthologous to genes associated with recessive resistance to Cry1Ac in Heliothis virescens and two other lepidopteran species, was expressed in the midgut. Sequences of 10 susceptible and seven resistant silkworm strains revealed a common tyrosine insertion in an outer loop of the predicted transmembrane structure of resistant alleles. We confirmed the role of this ATP-binding cassette transporter gene in Bt resistance by converting a resistant silkworm strain into a susceptible one by using germline transformation. This study represents a direct demonstration of Bt resistance gene function in insects with the use of transgenesis

Distribution of Virulence Markers among <em>Vibrio vulnificus</em> Isolates of Clinical and Environmental Origin and Regional Characteristics in Japan

<div><h3>Background</h3><p><em>Vibrio vulnificus</em> is an opportunistic human pathogen that is widely distributed in estuarine environments and is capable of causing necrotizing fasciitis and sepsis. In Japan, based on epidemiological research, the incidences of <em>V. vulnificus</em> were concentrated in Kyusyu, mainly in coastal areas of the Ariake Sea. To examine the virulence potential, various genotyping methods have recently been developed. This study aimed to investigate the distribution of virulence markers among <em>V. vulnificus</em> isolates of clinical and environmental origin in three coastal areas with different infection incidences and to determine whether these isolates have the siderophore encoding gene <em>viuB</em>.</p> <h3>Methodology/Principal Findings</h3><p>We examined the distribution of genotypes of the 16S ribosomal ribonucleic acid (rRNA) gene, <em>vvhA</em>, <em>vcg</em>, and capsular polysaccharide (CPS), and the presence of <em>viuB</em> in 156 isolates collected from patients and environmental samples in Japan. The environmental samples were collected from three coastal areas: the Ariake Sea, Ise & Mikawa Bay, and Karatsu Bay. The results showed disparity in the ratios of genotypes depending on the sample origins. <em>V. vulnificus</em> isolates obtained from patients were classified into the clinical type for all genotypes. In the environmental isolates, the ratios of the clinical type for genotypes of the 16S rRNA gene, <em>vvhA</em>, and <em>vcg</em> were in the order of the Ariake Sea>Ise & Mikawa Bay>Karatsu Bay. Meanwhile, CPS analysis showed no significant difference. Most isolates possessed <em>viuB</em>.</p> <h3>Conclusions</h3><p>Many <em>V. vulnificus</em> belonging to the clinical type existed in the Ariake Sea. Three coastal areas with different infection incidences showed distinct ratios of genotypes. This may indicate that the distribution of clinical isolates correlates with the incidence of <em>V. vulnificus</em> infection.</p> </div

Ratio of genotypic profile according to isolate origins.

<p>The ratio of profile of clinical and environmental isolates is shown. The three main genotypic profiles were combined. Profile 1 (clinical type) consisted of 16S rRNA gene type B, <i>vvhA</i> type 1, and <i>vcg</i> C-type; profile 2 (non-clinical type) consisted of type A, type 2, and E-type; and profile 4 consisted of type B, type 2 and C-type. Other combination types were set to untypeable.</p

Map of sampling points.

<p>The prefectures indicated by dots are areas where <i>V. vulnificus</i> infections occurred. 1, Saga; 2, Nagasaki; 3, Fukuoka; 4, Kumamoto; and 5, Aichi prefectures.</p

Distribution of genotypes and <i>viuB</i> proportion of <i>V. vulnificus</i> according to clinical and Ariake Sea isolates.

a<p>NA, not amplified.</p><p>rRNA, ribosomal ribonucleic acid; CPS, capsular polysaccharide.</p

Distribution of genotypes and <i>viuB</i> proportion of <i>V. vulnificus</i> according to environmental isolate origins.

a<p>NA, not amplified.</p><p>rRNA, ribosomal ribonucleic acid; CPS, capsular polysaccharide.</p