Giant fish-killing water bug reveals ancient and dynamic venom evolution in Heteroptera.

True Bugs (Insecta: Heteroptera) produce venom or saliva with diverse bioactivities depending on their feeding strategies. However, little is known about the molecular evolution of the venom toxins underlying these biological activities. We examined venom of the giant fish-killing water bug Lethocerus distinctifemur (Insecta: Belostomatidae) using infrared spectroscopy, transcriptomics, and proteomics. We report 132 venom proteins including putative enzymes, cytolytic toxins, and antimicrobial peptides. Over 73% (96 proteins) showed homology to venom proteins from assassin bugs (Reduviidae), including 21% (28 proteins from seven families) not known from other sources. These data suggest that numerous protein families were recruited into venom and diversified rapidly following the switch from phytophagy to predation by ancestral heteropterans, and then were retained over > 200 my of evolution. In contrast, trophic switches to blood-feeding (e.g. in Triatominae and Cimicidae) or reversions to plant-feeding (e.g., in Pentatomomorpha) were accompanied by rapid changes in the composition of venom/saliva, including the loss of many protein families.

Venom exaptation and adaptation during the trophic switch to blood-feeding by kissing bugs.

Kissing bugs are known to produce anticoagulant venom that facilitates blood-feeding. However, it is unknown how this saliva evolved and if the venom produced by the entomophagous ancestors of kissing bugs would have helped or hindered the trophic shift. In this study, we show that venoms produced by extant predatory assassin bugs have strong anticoagulant properties mediated chiefly by proteolytic degradation of fibrinogen, and additionally contain anticoagulant disulfide-rich peptides. However, venom produced by predatory species also has pain-inducing and membrane-permeabilizing activities that would be maladaptive for blood-feeding, and which venom of the blood-feeding species lack. This study demonstrates that venom produced by the predatory ancestors of kissing bugs was exapted for the trophic switch to blood-feeding by virtue of its anticoagulant properties. Further adaptation to blood-feeding occurred by downregulation of venom toxins with proteolytic, cytolytic, and pain-inducing activities, and upregulation and neofunctionalization of toxins with anticoagulant activity independent of proteolysis.

Transfer of quinolone resistance gene qnrA1 to Escherichia coli through a 50 kb conjugative plasmid resulting from the splitting of a 300 kb plasmid.

OBJECTIVES: To analyse the in vitro transfer of the qnrA1 gene by a 50 kb (pSZ50) self-transferable plasmid that derives from a 300 kb plasmid (pSZ300) and to determine the complete nucleotide sequence of plasmid pSZ50. METHODS: Extended-spectrum ß-lactamase (ESBL) and plasmid-mediated quinolone resistance (PMQR) genes of an Escherichia coli clinical isolate were analysed. Plasmid analysis included conjugation and selection on seven antibiotics examined by antimicrobial susceptibility testing, RFLP comparison, Southern hybridization, incompatibility group identification and shotgun sequencing. RESULTS: The E. coli 5509 isolate carries the genes encoding the ESBL CTX-M-15 and the quinolone resistance determinants qnrA1, qnrB2 and aac(6')-Ib-cr on a 300 kb plasmid. Seven transfer resistances were analysed by conjugation under two conditions (30 and 37°C), leading to two distinct transconjugant phenotypes with different resistances. Transconjugants of phenotype A harboured a 300 kb plasmid named pSZ300 that conferred resistance to eight antibiotics and harboured the qnrA1, aac(6')-Ib-cr and bla(CTX-M-15) genes. Transconjugants of phenotype B were resistant to three antibiotics and they harboured the qnrA1 gene on an ≈ 50 kb plasmid named pSZ50. Both plasmids were self-transferable at a frequency of 1 × 10(-3). Plasmid pSZ300 was typed to be both an IncF and IncN plasmid, whereas pSZ50 corresponded only to type IncN. Fingerprinting and Southern hybridization showed that plasmid pSZ50 derived from pSZ300. The complete nucleotide sequence of plasmid pSZ50 was determined (51556 bp) and 55 open reading frames were predicted. The qnrA1 gene was identified in a tandem duplicate inside a sul1-type integron structure. CONCLUSIONS: The plasmid pSZ300 represented a fusion of two replicons (IncF and IncN), and our observations suggest that the plasmid pSZ50 (IncN) may split and transfer antibiotic resistance determinants. This mechanism could be advantageous in the dissemination of antibiotic resistance genes.