Molecular epidemiology of norovirus gastroenteritis in children in Jiangmen, China, 2005-2007

Human noroviruses (NoVs) are an important cause of epidemic acute gastroenteritis. Their role in sporadic cases, however, is less clear. In this study, we performed a two-year surveillance (September 2005 to August 2007) of NoV gastroenteritis in outpatient clinics in a southern city of China, Jiangmen City. NoVs were detected in 115 patients (115/881, 13.1%) with 30 (26.1%) co-infections with rotaviruses. Sequence analysis showed that all 115 NoVs belonged to genogroup II, with GII.4 being the most predominant (87.8%). NoV-associated infection can be seen year-around, with autumn and winter peaks. This study provides basic information on sporadic cases of major NoV gastroenteritis in children in different seasons, which is valuable for future disease control and prevention.

Detection and genomic characterization of new avian-like hepatitis E virus in a sparrow in the United States

Hepatitis E virus (HEV) is a nonenveloped, positive-sense, single-stranded RNA virus that has been detected in a wide variety of animals. In 2017, an avian-like HEV was identified in sparrow feces sampled from around a pig farm in the midwestern United States. Sequence analysis revealed that the sparrow isolate represents a novel HEV that is distantly related to chicken and little egret HEVs.

Genomics accurately predicts antimicrobial resistance in Staphylococcus pseudintermedius collected as part of Vet-LIRN resistance monitoring

Whole-genome sequencing (WGS) has changed our understanding of bacterial pathogens, aiding outbreak investigations and advancing our knowledge of their genetic features. However, there has been limited use of genomics to understand antimicrobial resistance of veterinary pathogens, which would help identify emerging resistance mechanisms and track their spread. The objectives of this study were to evaluate the correlation between resistance genotypes and phenotypes for Staphylococcus pseudintermedius, a major pathogen of companion animals, by comparing broth microdilution antimicrobial susceptibility testing and WGS. From 2017-2019, we conducted antimicrobial susceptibility testing and WGS on S. pseudintermedius isolates collected from dogs in the United States as a part of the Veterinary Laboratory Investigation and Response Network (Vet-LIRN) antimicrobial resistance monitoring program. Across thirteen antimicrobials in nine classes, resistance genotypes correlated with clinical resistance phenotypes 98.4 % of the time among a collection of 592 isolates. Our findings represent isolates from diverse lineages based on phylogenetic analyses, and these strong correlations are comparable to those from studies of several human pathogens such as Staphylococcus aureus and Salmonella enterica. We uncovered some important findings, including that 32.3 % of isolates had the mecA gene, which correlated with oxacillin resistance 97.0 % of the time. We also identified a novel rpoB mutation likely encoding rifampin resistance. These results show the value in using WGS to assess antimicrobial resistance in veterinary pathogens and to reveal putative new mechanisms of resistance.

Genetic characterization and recombination analysis of atypical porcine pestivirus

Atypical porcine pestivirus (APPV) is recognised as the etiology of congenital tremor (CT) Type A-II and poses a challenge to pig production. Here, we described a CT case in piglets caused by APPV infection in central China in 2017. Interestingly, different from a previous report, more CT litters were observed in the second and third parity sows compared to the first and fourth parity. Evolutionary analysis and recombination evaluation were conducted for the isolate and 61 APPV genomes were available in GenBank. Phylogenetic analysis revealed a high level of genetic variation of APPV and the coexistence of three clades (Clades I-III) in China. The isolate was clustered into Clade I, which seemed to be prevalent worldwide and displayed higher genetic variability (Subgroups 1-4) compared with Clade II and Clade III, both of which were only reported in China. Notably, three putative recombinants were identified and characterized in APPV. The recombination events occurred in inter-clades (Clade II and III) or intra-clades (Clade I). To the best of our knowledge, this study presents the first evidence of homologous recombination within Pestivirus K. These results provide new clinical presentations of APPV infection and may be helpful in better understanding the large amount of genetic variations in this genus.

Development of a duplex SYBR GreenⅠ based real-time PCR assay for detection of porcine epidemic diarrhea virus and porcine bocavirus3/4/5

The duplex real-time PCR assay based on SYBR Green І was developed for detection of porcine epidemic diarrhea virus (PEDV) and porcine bocavirus (PBoV) 3/4/5 genotypes simultaneously. Two pairs of specific primers were designed targeting the N gene sequence of PEDV and VP1 gene sequence of PBoV3/4/5. PEDV and PBoV3/4/5 could be distinguished by their different melting temperatures (Tm) in one sample. The Tm value of PEDV was 83.5 °C, and the Tm value of PBoV3/4/5 was 78.5 °C, while other swine pathogens showed no specific melting peaks. The detection limits of this assay were 10 copies/μL for both PEDV and PBoV3/4/5. A total of sixty-three intestinal tissue samples were collected from piglets suffering from diarrhea, and the viral nucleic acids detected and identified by the real-time PCR assay and conventional PCR assay. The duplex real-time PCR detection results showed that the prevalence of PEDV and PBoV3/4/5 was 85.7% and 46%, respectively, and the co-infection rate of the two viruses was 28.6%. These results indicated that this duplex real-time PCR assay was a sensitive, specific and reproducible method for differentiating PEDV and PBoV3/4/5 or their co-infection.

Bovine kobuvirus-A comprehensive review

Bovine kobuvirus (BKV) is a single-stranded, positive sense, non-enveloped RNA virus in genus Kobuvirus of family Picornavirus. BKV was first identified in the culture media of HeLa cell containing calf serum in 2003. Since then, BKV has been detected in 13 countries of four different continents, suggesting widespread in the world. Herein, we review the detection and genomic characterization of BKV in 13 countries. All studies tested bovine faecal samples for BKV. These studies provide evidence that BKV might be a causative agent for neonatal calf diarrhoea. Therefore, further efforts including animal challenge study are urgently needed to unveil the pathogenicity of BKV.

Mitigation of SARS-CoV-2 transmission at a large public university

In Fall 2020, universities saw extensive transmission of SARS-CoV-2 among their populations, threatening health of the university and surrounding communities, and viability of in-person instruction. Here we report a case study at the University of Illinois at Urbana-Champaign, where a multimodal "SHIELD: Target, Test, and Tell" program, with other non-pharmaceutical interventions, was employed to keep classrooms and laboratories open. The program included epidemiological modeling and surveillance, fast/frequent testing using a novel low-cost and scalable saliva-based RT-qPCR assay for SARS-CoV-2 that bypasses RNA extraction, called covidSHIELD, and digital tools for communication and compliance. In Fall 2020, we performed >1,000,000 covidSHIELD tests, positivity rates remained low, we had zero COVID-19-related hospitalizations or deaths amongst our university community, and mortality in the surrounding Champaign County was reduced more than 4-fold relative to expected. This case study shows that fast/frequent testing and other interventions mitigated transmission of SARS-CoV-2 at a large public university.

Genetic characterization of extraintestinal Escherichia coli isolates from chicken, cow and swine

Phenotypic determination of antimicrobial resistance in bacteria is very important for diagnosis and treatment, but sometimes this procedure needs further genetic evaluation. Whole-genome sequencing plays a critical role in deciphering and advancing our understanding of bacterial evolution, transmission, and surveillance of antimicrobial resistance. In this study, whole-genome sequencing was performed on nineteen clinically extraintestinal Escherichia coli isolates from chicken, cows and swine and showing different antimicrobial susceptibility. A total of 44 different genes conferring resistance to 11 classes of antimicrobials were detected in 15 of 19 E. coli isolates (78.9%), and 22 types of plasmids were detected in 15/19 (78.9%) isolates. In addition, whole-genome sequencing of these 19 isolates identified 111 potential virulence factors, and 53 of these VFDB-annotated genes were carried by all these 19 isolates. Twelve different virulence genes were identified while the most frequent ones were gad (glutamate decarboxylase), iss (increased serum survival) and lpfA (long polar fimbriae). All isolates harbored at least one of the virulence genes. The findings from comparative genomic analyses of the 19 diverse E. coli isolates in this study provided insights into molecular basis of the rising multi-drug resistance in E. coli.

Genetically divergent porcine sapovirus identified in pigs, United States

Porcine sapoviruses (SaVs) are genetically diverse and widely distributed in pig-producing countries. Eight genogroups of porcine SaV have been identified, and genogroup III is the predominant type. Most of the eight genogroups of porcine SaV are circulating in the United States. In the present study, we report detection of porcine SaVs in pigs at different ages with clinical diarrhoea using next-generation sequencing and genetic characterization. All seven cases have porcine SaV GIII strains detected and one pooled case was found to have a porcine SaV GVI strain IA27912-B-2018. Sequence analysis showed that seven GIII isolates were genetically divergent and formed four different lineages on the trees of complete genome, RdRP, VP1 and VP2. In addition, these seven GIII isolates had three different deletion/insertion patterns in an identified variable region close to the 3' end of VP2. The GVI strain IA27912-B-2018 was closely related to strains previously detected in the United States and Japan. A 3-nt deletion in VP1 region of GVI IA27912-B-2018 was identified. Our study showed that genetically divergent SaVs of different genogroups are co-circulating in pigs in the United States. Future studies comparing the virulence of these different genogroups in pigs are needed to better understand this virus and to determine if surveillance and vaccine development are needed to monitor and control porcine SaVs.

Strain-specific interaction of a GII.10 Norovirus with HBGAs

Noroviruses (NoVs), an important cause of gastroenteritis in humans, recognize human histo-blood group antigens (HBGAs) as receptors. The crystal structures of the protruding (P) domain of a GII.10 NoV (Vietnam 026) in complex with various HBGA oligosaccharides were elucidated. However, the HBGA binding profile of this virus remains unknown. In this study, we determined the saliva and oligosaccharide binding profiles of this virus and the roles of amino acids that are involved in HBGA binding. Our data showed that Vietnam 026 bound to all ABO secretor and non-secretor saliva with clear signals detected by monoclonal antibodies against H3, H1, Le(y), Le(a) and sialyl Le(a). Mutagenesis study confirmed the binding site determined by the crystallography study, in which single mutations wiped out the binding function. We also identified amino acids surrounding the central binding pocket that may participate in the binding by affecting the HBGA binding specificity of the GII.10 NoV.

A novel approach to concentrate human and animal viruses from wastewater using receptors-conjugated magnetic beads

Viruses are present at low concentrations in wastewater; therefore, an effective method for concentrating virus particles is necessary for accurate wastewater-based epidemiology (WBE). We designed a novel approach to concentrate human and animal viruses from wastewater using porcine gastric mucin-conjugated magnetic beads (PGM-MBs). We systematically evaluated the performances of the PGM-MBs method (sensitivity, specificity, and robustness to environmental inhibitors) with six viral species, including Tulane virus (a surrogate for human norovirus), rotavirus, adenovirus, porcine coronavirus (transmissible gastroenteritis virus or TGEV), and two human coronaviruses (NL63 and SARS-CoV-2) in influent wastewater and raw sewage samples. We determined the multiplication factor (the ratio of genome concentration of the final solution to that of the initial solution) for the PGM-MBs method, which ranged from 1.3 to 64.0 depending on the viral species. Because the recovery efficiency was significantly higher when calculated with virus titers than it was with genome concentration, the PGM-MBs method could be an appropriate tool for assessing the risk to humans who are inadvertently exposed to wastewater contaminated with infectious viruses. Furthermore, PCR inhibitors were not concentrated by PGM-MBs, suggesting that this tool will be successful for use with environmental samples. In addition, the PGM-MBs method is cost-effective (0.5 USD/sample) and has a fast turnaround time (3 h from virus concentration to genome quantification). Thus, this method can be implemented in high throughput facilities. Because of its strong performance, intrinsic characteristics of targeting the infectious virus, robustness to wastewater, and adaptability to high throughput systems, the PGM-MBs method can be successfully applied to WBE and ultimately provides valuable public health information.

Genetic and phylogenetic analysis of a novel parvovirus isolated from chickens in Guangxi, China

A previously unidentified chicken parvovirus (ChPV) strain, associated with runting-stunting syndrome (RSS), is now endemic among chickens in China. To explore the genetic diversity of ChPV strains, we determined the first complete genome sequence of a novel ChPV isolate (GX-CH-PV-7) identified in chickens in Guang Xi, China, and showed moderate genome sequence similarity to reference strains. Analysis showed that the viral genome sequence is 86.4 %-93.9 % identical to those of other ChPVs. Genetic and phylogenetic analyses showed that this newly emergent GX-CH-PV-7 is closely related to Gallus gallus enteric parvovirus isolate ChPV 798 from the USA, indicating that they may share a common ancestor. The complete DNA sequence is 4612 bp long with an A+T content of 56.66 %. We determined the first complete genome sequence of a previously unidentified ChPV strain to elucidate its origin and evolutionary status.

Antibody Responses to SARS-CoV-2 Antigens in Humans and Animals

To optimize the public health response to coronavirus disease 2019 (COVID-19), we must first understand the antibody response to individual proteins on the severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) and the antibody's cross reactivity to other coronaviruses. Using a panel of 37 convalescent COVID-19 human serum samples, we showed that the magnitude and specificity of responses varied across individuals, independent of their reactivity to seasonal human coronaviruses (HCoVs). These data suggest that COVID-19 vaccines will elicit primary humoral immune responses in naïve individuals and variable responses in those previously exposed to SARS-CoV-2. Unlike the limited cross-coronavirus reactivities in humans, serum samples from 96 dogs and 10 cats showed SARS-CoV-2 protein-specific responses focused on non-S1 proteins. The correlation of this response with those to other coronaviruses suggests that the antibodies are cross-reactive and generated to endemic viruses within these hosts, which must be considered in seroepidemiologic studies. We conclude that substantial variation in antibody generation against coronavirus proteins will influence interpretations of serologic data in the clinical and veterinary settings.

Design of SARS-CoV-2 Variant-Specific PCR Assays Considering Regional and Temporal Characteristics

Monitoring the prevalence of SARS-CoV-2 variants is necessary to make informed public health decisions during the COVID-19 pandemic. PCR assays have received global attention, facilitating a rapid understanding of variant dynamics because they are more accessible and scalable than genome sequencing. However, as PCR assays target only a few mutations, their accuracy could be reduced when these mutations are not exclusive to the target variants. Here we introduce PRIMES, an algorithm that evaluates the sensitivity and specificity of SARS-CoV-2 variant-specific PCR assays across different geographical regions by incorporating sequences deposited in the GISAID database. Using PRIMES, we determined that the accuracy of several PCR assays decreased when applied beyond the geographic scope of the study in which the assays were developed. Subsequently, we used this tool to design Alpha and Delta variant-specific PCR assays for samples from Illinois, USA. In silico analysis using PRIMES determined the sensitivity/specificity to be 0.99/0.99 for the Alpha variant-specific PCR assay and 0.98/1.00 for the Delta variant-specific PCR assay in Illinois, respectively. We applied these two variant-specific PCR assays to six local sewage samples and determined the dominant SARS-CoV-2 variant of either the wild type, the Alpha variant, or the Delta variant. Using next-generation sequencing (NGS) of the spike (S) gene amplicons of the Delta variant-dominant samples, we found six mutations exclusive to the Delta variant (S:T19R, S:Δ156/157, S:L452R, S:T478K, S:P681R, and S:D950N). The consistency between the variant-specific PCR assays and the NGS results supports the applicability of PRIMES. IMPORTANCE Monitoring the introduction and prevalence of variants of concern (VOCs) and variants of interest (VOIs) in a community can help the local authorities make informed public health decisions. PCR assays can be designed to keep track of SARS-CoV-2 variants by measuring unique mutation markers that are exclusive to the target variants. However, the mutation markers may not be exclusive to the target variants because of regional and temporal differences in variant dynamics. We introduce PRIMES, an algorithm that enables the design of reliable PCR assays for variant detection. Because PCR is more accessible, scalable, and robust for sewage samples than sequencing technology, our findings will contribute to improving global SARS-CoV-2 variant surveillance.

Detection and genetic characterization of porcine pegivirus in pigs in the United States

Using next-generation sequencing on vesicular swab and serum from swine from the USA exhibiting lameness and vesicles, porcine pegivirus (PPgV) was first identified and genetically characterized in the United States. Further screening using RT-PCR revealed that 24 of 159 (15.1%) serum samples were positive for PPgV. Future studies are needed to understand clinical impacts of the virus.

Complete Genome Sequence of Porcine Coronavirus HKU15 Strain IN2847 from the United States

Porcine coronavirus HKU15 (PorCoV HKU15) was first detected in pigs with clinical diseases in February 2014 in the United States. Here, we report the complete genome sequence of Indiana strain IN2847, which might be useful for understanding the molecular profile of PorCoV HKU15.

Astrovirus in White-Tailed Deer, United States, 2018

We report the identification of astrovirus WI65268 in a white-tailed deer with respiratory disease in the United States in 2018. This virus is a recombinant of Kagoshima1-7 and Kagoshima2-3-2 (both bovine astroviruses from Japan) and was characterized as a potential new genotype. Further surveillance of deer might help identify related isolates.

Detection and Characterization of New Coronavirus in Bottlenose Dolphin, United States, 2019

We characterized novel coronaviruses detected in US bottlenose dolphins (BdCoVs) with diarrhea. These viruses are closely related to the other 2 known cetacean coronaviruses, Hong Kong BdCoV and beluga whale CoV. A deletion in the spike gene and insertions in the membrane gene and untranslated regions were found in US BdCoVs (unrelated to severe acute respiratory syndrome coronavirus 2).

Sequencing and phylogenetic characterization of Brucella canis isolates, Ohio, 2016

Brucella canis is one of zoonotic pathogens causing infection in human. In this study, we isolated and sequenced 38 B. canis strains from 11 cases. Core genome multilocus sequence typing analysis classified all B. canis isolates into two genogroups, GI and GII. All 38 isolates cluster together forming a 2016 Ohio cluster, in which they form five subclusters reflecting their geographical differences. Unlike GI, the isolates of the GII are from diverse geographical locations including Asia, America, Africa, and Europe and form Asia and South America clusters. Overall, our findings could be useful to investigate and track B. canis of future outbreaks.

Detection of influenza viral gene in European starlings and experimental infection

BACKGROUND

European starlings (Sturnus vulgaris) are common, widely distributed birds in North America that frequently come into contact with agricultural operations. However, starlings have been one of the neglected land-based wild bird species for influenza surveillance.

OBJECTIVES

To study the potential role of starlings in the ecology and epidemiology of influenza virus.

METHODS

We collected 328 digestive and 156 tracheal samples from starlings in Ohio in years 2007 (July) to 2008 (August) and screened for the presence of influenza virus by real-time RT-PCR, standard RT-PCR and virus isolation using embryonated chicken eggs. In addition, we conducted an experimental infection study to evaluate the replication and induction of antibody response by two low pathogenic avian influenza (AI) viruses in starlings.

RESULTS

Although virus isolation was negative, we confirmed 21 influenza positive digestive and tracheal samples by real-time and standard RT-PCR tests. Phylogenetic analysis revealed that five NS genes recovered from Starlings belonged to NS subtype A and were most similar to the NS genes from a wild aquatic bird origin isolate from Ohio. Experimental infection studies using two low pathogenic AI strains showed that starlings could be infected, shed virus, and seroconvert.

CONCLUSIONS

This study shows that starlings can carry influenza virus that is genetically similar to wild aquatic bird origin strains and may serve as a carrier of influenza virus to domestic animals.

Development of DIVA (differentiation of infected from vaccinated animals) vaccines utilizing heterologous NA and NS1 protein strategies for the control of triple reassortant H3N2 influenza in turkeys

Since 2003, triple reassortant (TR) swine H3N2 influenza viruses containing gene segments from human, avian, and swine origins have been detected in the U.S. turkey populations. The initial outbreak that occurred involved birds that were vaccinated with the currently available H3 swine- and avian-origin influenza vaccines. Antigenically, all turkey swine-lineage TR H3N2 isolates are closely related to each other but show little or no antigenic cross-reactivity with the avian origin or swine origin influenza vaccine strains that are currently being used in turkey operations. These results call for re-evaluation of currently available influenza vaccines being used in turkey flocks and development of more effective DIVA (differentiation of infected from vaccinated animals) vaccines. In this study, we selected one TR H3N2 strain, A/turkey/OH/313053/04 (H3N2) that showed broad cross reactivity with other recent TR turkey H3N2 isolates, and created NA- and NS-based DIVA vaccines using traditional reassortment as well as reverse genetics methods. Protective efficacy of those vaccines was determined in 2-week-old and 80-week-old breeder turkeys. The reassortant DIVA vaccines significantly reduced the presence of challenge virus in the oviduct of breeder turkeys as well as trachea and cloaca shedding of both young and old breeder turkeys, suggesting that proper vaccination could effectively prevent egg production drop and potential viral contamination of eggs in infected turkeys. Our results demonstrate that the heterologous NA and NS1 DIVA vaccines together with their corresponding serological tests could be useful for the control of TR H3N2 influenza in turkeys.

Detection and genetic characterization of porcine pegivirus from pigs in China

Porcine pegiviruses (PPgV) have been first discovered in serum samples from domestic pigs in Germany in 2016 and then in the USA in 2018. To date, there is no documentation with respect to the presence of PPgVs in domestic pigs in China. Herein, we attempted to determine the presence and prevalence of PPgV in China and its genetic characterization. In this study, 469 sera were tested and 34 (7.25%) were positive for PPgV. An ascending trend of the positive rate for PPgV was observed from suckling piglets (1.61%) to nursing piglets (1.85%), finishing pigs (6.56%), and sows (11.34%). The complete genome sequence of a representative strain of PPgV, PPgV_GDCH2017, and the complete E2 gene of 17 PPgV isolates discovered in this study was determined. Sequence analysis indicated that PPgV_GDCH2017 was highly related to other PPgVs with nucleotide and amino acid identities ranging from 87.3 to 97.4% and 94.6-99.3%, respectively, in the complete coding region. Phylogenetic analyses demonstrated that the PPgV_GDCH2017 discovered in this study was closely related to the PPgVs from the USA and clustered in the same genus with pegiviruses from other hosts. The topology of the phylogenetic tree based on the complete E2 gene was consistent with that based on the complete genome of PPgV. Further studies on pathogenicity and pathogenesis of PPgVs are needed.

US variant porcine epidemic diarrhea virus: histological lesions and genetic characterization

Porcine epidemic diarrhea virus (PEDV) was first recognized in pigs in the United States (US) in May 2013. Since then, the virus has spread to over 30 states and caused significant economic losses in the US swine industry due to the high mortality in newborn piglets less than 2 weeks of age. A mild-variant strain OH851 of PEDV in the US was first reported in January 2014. Here, we report histological changes in the small intestines of five piglets infected with the variant strain OH851 of PEDV. The lesions observed were milder, compared to the US classical strain of PEDV. Our study, for the first time, reports the histological lesions caused by the variant PEDV OH851 strain from a field case. In addition, genomic characterization demonstrated that US variant PEDV is more closely related to European-like strains in the first 1170 nt of the 5' spike gene but to US classical PEDV strains in the remaining genome, suggesting that the variant PEDV strain may derive from a recombinant event between the US classical and European-like PEDV strains.

Comparative genomic analysis of Bordetella bronchiseptica isolates from the lungs of pigs with porcine respiratory disease complex (PRDC)

BACKGROUND

Bordetella bronchiseptica (B. bronchiseptica), as an opportunistic pathogen, can cause respiratory diseases in a variety of animals, including humans. In additional to being involved in porcine atrophic rhinitis through coinfection with Pasteurella multocida, B. bronchiseptica is associated with porcine respiratory disease complex (PRDC). While there are genomic data available from different host species, little is known about B. bronchiseptica isolates from pig lungs, especially from lungs characterized as having PRDC.

RESULTS

A total of five B. bronchiseptica isolates were identified from pig lungs characterized as PRDC. The draft genomes of these strains were generated. In comparison with the other reported genomes, these five isolates showed the similar general characteristic including G+C content, rRNAs/tRNA, and clusters of orthologous groups of proteins (COGs). Phylogenetic analysis of all B. Bronchiseptica isolates of different species available at GenBank based on core genome multilocus sequence typing (cgMLST) classified them into two genogroups. All five isolates from this study, with the other isolates from pigs, were placed into a subclade of genogroup I consisting of only mammalian isolates. By contrast, genogroup II contained the isolates from an avian species (turkey) and some mammals (human and dog). Moreover, genome annotation revealed the presence of antibiotic resistance genes and virulence genes among these five genomes, consistent with the similarity and variety in genomic traits. Finally, comparative analysis of insertion sequence (IS) and prophages in five genomes further showed the similarity and variety in genomic characteristic.

CONCLUSIONS

This is the first study to provide comparative genomics of B. bronchiseptica strains from pig lungs characterized as having PRDC. Importantly, the findings presented in this study reveal novel genomic characteristic of B. bronchiseptica, which should provide insightful information on genome evolution.