The genome of VP3, a T7-like phage used for the typing of Vibrio cholerae

Screening of Potential Vibrio cholerae Bacteriophages for Cholera Therapy: A Comparative Genomic Approach

Cholera continues to be a major burden for developing nations, especially where sanitation, quality of water supply, and hospitalization have remained an issue. Recently, growing antimicrobial-resistant strains of Vibrio cholerae underscores alternative therapeutic strategies for cholera. Bacteriophage therapy is considered one of the best alternatives for antibiotic treatment. For the identification of potential therapeutic phages for cholera, we have introduced a comprehensive comparative analysis of whole-genome sequences of 86 Vibrio cholerae phages. We have witnessed extensive variation in genome size (ranging from 33 to 148 kbp), GC (G + C) content (varies from 34.5 to 50.8%), and the number of proteins (ranging from 15 to 232). We have identified nine clusters and three singletons using BLASTn, confirmed by nucleotide dot plot and sequence identity. A high degree of sequence and functional similarities in both the genomic and proteomic levels have been observed within the clusters. Evolutionary analysis confirms that phages are conserved within the clusters but diverse between the clusters. For each therapeutic phage, the top 2 closest phages have been identified using a system biology approach and proposed as potential therapeutic phages for cholera. This method can be applied for the classification of the newly isolated Vibrio cholerae phage. Furthermore, this systematic approach might be useful as a model for screening potential therapeutic phages for other bacterial diseases.

Vgas: A Viral Genome Annotation System

The in-depth study of viral genomes is of great help in many aspects, especially in the treatment of human diseases caused by viral infections. With the rapid accumulation of viral sequencing data, improved, or alternative gene-finding systems have become necessary to process and mine these data. In this article, we present Vgas, a system combining an ab initio method and a similarity-based method to automatically find viral genes and perform gene function annotation. Vgas was compared with existing programs, such as Prodigal, GeneMarkS, and Glimmer. Through testing 5,705 virus genomes downloaded from RefSeq, Vgas demonstrated its superiority with the highest average precision and recall (both indexes were 1% higher or more than the other programs); particularly for small virus genomes (≤ 10 kb), it showed significantly improved performance (precision was 6% higher, and recall was 2% higher). Moreover, Vgas presents an annotation module to provide functional information for predicted genes based on BLASTp alignment. This characteristic may be specifically useful in some cases. When combining Vgas with GeneMarkS and Prodigal, better prediction results could be obtained than with each of the three individual programs, suggesting that collaborative prediction using several different software programs is an alternative for gene prediction. Vgas is freely available at http://cefg.uestc.cn/vgas/ or http://121.48.162.133/vgas/. We hope that Vgas could be an alternative virus gene finder to annotate new genomes or reannotate existing genome.

The outer-membrane protein TolC of Vibrio cholerae serves as a second cell-surface receptor for the VP3 phage

Receptor recognition is a key step in the initiation of phage infection. Previously, we found that VP3, the T7 family phage of the Vibrio cholerae serogroup O1 biotype El Tor, can adsorb the core oligosaccharide (OS) of lipopolysaccharides of V. cholerae However, some wildtype strains of V. cholerae possessing the intact OS gene cluster still have VP3 binding but are resistant to VP3 infection. Moreover, an OS gene-deletion mutant still exhibits weak VP3 binding, suggesting multiple factors are possibly involved in VP3 binding to V. cholerae Here, we report that the outer-membrane protein TolC of V. cholerae is involved in the host adsorption of VP3. We observed that TolC directly interacts with the VP3 tail fiber protein gp44 and its C-terminal domains, and we also found that three amino acid residues in the outside loops of TolC, at positions 78, 290, and 291, are critical for binding to gp44. Among the VP3-resistant wildtype V. cholerae strains, frequent amino acid residue mutations were observed in the loops around the sites 78, 290, and 291, which were predicted to be exposed to the cell surface. These findings reveal a co-receptor-binding mechanism for VP3 infection of V. cholerae and that both outer-membrane TolC and OS are necessary for successful VP3 infection of V. cholerae We conclude that mutations on the outside loops of the receptor may confer V. cholerae strains with VP3 phage resistance, enabling these strains to survive in environments containing VP3 or related phages.

The Resistance of Vibrio cholerae O1 El Tor Strains to the Typing Phage 919TP, a Member of K139 Phage Family

Bacteriophage 919TP is a temperate phage of Vibrio cholerae serogroup O1 El Tor and is used as a subtyping phage in the phage-biotyping scheme in cholera surveillance in China. In this study, sequencing of the 919TP genome showed that it belonged to the Vibrio phage K139 family. The mechanisms conferring resistance to 919TP infection of El Tor strains were explored to help understand the subtyping basis of phage 919TP and mutations related to 919TP resistance. Among the test strains resistant to phage 919TP, most contained the temperate 919TP phage genome, which facilitated superinfection exclusion to 919TP. Our data suggested that this immunity to Vibrio phage 919TP occurred after absorption of the phage onto the bacteria. Other strains contained LPS receptor synthesis gene mutations that disable adsorption of phage 919TP. Several strains resistant to 919TP infection possessed unknown resistance mechanisms, since they did not contain LPS receptor mutations or temperate K139 phage genome. Further research is required to elucidate the phage infection steps involved in the resistance of these strains to phage infection.

Recognition of Protein-coding Genes Based on Z-curve Algorithms

Recognition of protein-coding genes, a classical bioinformatics issue, is an absolutely needed step for annotating newly sequenced genomes. The Z-curve algorithm, as one of the most effective methods on this issue, has been successfully applied in annotating or re-annotating many genomes, including those of bacteria, archaea and viruses. Two Z-curve based ab initio gene-finding programs have been developed: ZCURVE (for bacteria and archaea) and ZCURVE_V (for viruses and phages). ZCURVE_C (for 57 bacteria) and Zfisher (for any bacterium) are web servers for re-annotation of bacterial and archaeal genomes. The above four tools can be used for genome annotation or re-annotation, either independently or combined with the other gene-finding programs. In addition to recognizing protein-coding genes and exons, Z-curve algorithms are also effective in recognizing promoters and translation start sites. Here, we summarize the applications of Z-curve algorithms in gene finding and genome annotation.

Complete genome sequence of 285P, a novel T7-like polyvalent E. coli bacteriophage

Bacteriophages are considered potential biological agents for the control of infectious diseases and environmental disinfection. Here, we describe a novel T7-like polyvalent Escherichia coli bacteriophage, designated "285P," which can lyse several strains of E. coli. The genome, which consists of 39,270 base pairs with a G+C content of 48.73 %, was sequenced and annotated. Forty-three potential open reading frames were identified using bioinformatics tools. Based on whole-genome sequence comparison, phage 285P was identified as a novel strain of subgroup T7. It showed strongest sequence similarity to Kluyvera phage Kvp1. The phylogenetic analyses of both non-structural proteins (endonuclease gp3, amidase gp3.5, DNA primase/helicase gp4, DNA polymerase gp5, and exonuclease gp6) and structural protein (tail fiber protein gp17) led to the identification of 285P as T7-like phage. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analyses verified the annotation of the structural proteins (major capsid protein gp10a, tail protein gp12, and tail fiber protein gp17).