HORIZONTALLY TRANSFERRED GENES IN THE GENOME OF PENAEOIDEA SHRIMPS, Litopenaeus vannamei AND Fenneropenaeus chinensis

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 the members of the phylum Arthropoda, the Penaeoidea shrimps have to adapt to the complex water environments with various symbiotic or parasitic microorganisms, which provide a platform for horizontal gene transfer (HGT). Especially for the White spot syndrome virus (WSSV) and Vibrio parahaemolyticus (the major pathogen of EMS), which were found to be the two major pathogens to cause shrimps death in recent years.

In this study, we analyzed the genome-wide HGT events in the Pacific white shrimp Litopenaeus vannamei and the Chinese shrimp Fenneropenaeus chinensis，both samples were from shrimp culture farms in China. Through homology search and phylogenetic analysis, followed by experimental PCR confirmation, 14 genes and 9 genes with HGT event were identified in L. vannamei and F. chinensis, respectively. None of homologous sequences have been found between the genomes of WSSV and shrimps, indicating HGT events may have not happened between them. Whereas, there was a large genomic segements (about 3.7 Kb) of V. parahaemolyticus genome showed homologous to shrimps genomes, and a candidate HGT gene have been detected between them. Among the 14 HGT genes in L. vannamei, 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.

HGT events from bacteria or fungi were happened in shrimp genomes, and these horizontally transferred genes can be transcribed in shrimp. Importantly, most of these genes are exposed to a negative selection pressure and appeared to be functional. These HGT events may be beneficial for the development of the energy metabolism and defense mechanism in shrimps.