Horizontal transfer in bacterial Methionyl tRNA synthetase is very common shown by Genus and phyla level phylogenetic analysis

Abstract

Methionyl tRNA synthetase is single copy informational gene in Salmonella typhimurium. Informational genes are more conserved than operational genes. In this study we had analyzed HGT events within MetG sequences of different bacterial genera. A species tree based on 16srRNA sequences of the same genus was drawn evaluated against the generally accepted species tree of the bacteria. MetG phylogenetic tree was evaluated against the 16srRNAS tree and HGT event identified. Similarly phyla trees were made and HGT event identified. 24 HGT events were identified between genus and 11 within phyla. MetG is a considered as conserved gene finding so many HGT event in this gene indicate that horizontal gene transfer is very common in this gene. Manual tree making for phyla could help to understand phylogenetic relationships between very large trees.Key Terms:-Methionyl tRNA synthetase, Topological difference, Robinson Fould Distance, MEGA.When the HGT was compared between phyla 11 HGT ( Fig.7) incidences were found, this suggest that HGT within phyla is less common than genus. It has been suggested that HGT is dependent on evolutionary distance [12,[41][42][43][44].Our results are in accordance with this fact. This is the first description of HGT within phyla and genus tree. Phyla level HGT by virtue of its relative simplistic network in comparison to genus network may help to understand jumbled network created by intensive gene transfer events which some author predict could replace classical rRNA based phylogeny [10, 11, 45, 46]. Materials and Methods:- Retrieval of MetG Sequences:-Salmonella enterica subsp. Entericaserovar Typhimurium genome sequence and other 57 amino acid sequences in fasta file format were retrieved from NCBI.The 16SrRNA for creating species phylogeny for corresponding genus mentioned in metG sequences were downloaded from Ribosomal Database-Silva from www.arb-silva.de [28]. Alignment of MetG and 16SrRNA sequences:-The alignments of sequences were performed in MEGA [29] using Muscle. Unaligned region of alignment were removed. The Evolutionary analysisEvolutionary analysis was done in MEGA [30][31][32] and the methods used were Maximum Likelihood tree, Neighbour Joning tree, Minimum Evolution tree, Maximum Parsimony tree and UPGMA.Test of reliability was Bootstrap method[33]with 500 replications. In order to keep things simple we have kept captions givenin MEGA with minor changes for each figures to get information regarding methodology of tree analysis.