Horizontally transferred genes in the genome of Pacific white shrimp, Litopenaeus vannamei

Background: In recent years, as the development of next-generation sequencing technology, a growing number of genes have been reported as being horizontally transferred from prokaryotes to eukaryotes, most of them involving arthropods. As a member of the phylum Arthropoda, the Pacific white shrimp Litopenaeus vannamei has to adapt to the complex water environments with various symbiotic or parasitic microorganisms, which provide a platform for horizontal gene transfer (HGT). Results: In this study, we analyzed the genome-wide HGT events in L. vannamei. Through homology search and phylogenetic analysis, followed by experimental PCR confirmation, 14 genes with HGT event were identified: 12 of them were transferred from bacteria and two from fungi. Structure analysis of these genes showed that the introns of the two fungi-originated genes were substituted by shrimp DNA fragment, two genes transferred from bacteria had shrimp specific introns inserted in them. Furthermore, around other three bacteria-originated genes, there were three large DNA segments inserted into the shrimp genome. One segment was a transposon that fully transferred, and the other two segments contained only coding regions of bacteria. Functional prediction of these 14 genes showed that 6 of them might be related to energy metabolism, and 4 others related to defense of the organism. Conclusions: HGT events from bacteria or fungi were happened in the genome of L. vannamei, and these horizontally transferred genes can be transcribed in shrimp. This is the first time to report the existence of horizontally transferred genes in shrimp. Importantly, most of these genes are exposed to a negative selection pressure and appeared to be functional.