Comparative genomic analysis provides insights into the genetic diversity and pathogenicity of the genus Brucella.

Some Brucella spp. are important pathogens. According to the latest prokaryotic taxonomy, the Brucella genus consists of facultative intracellular parasitic Brucella species and extracellular opportunistic or environmental Brucella species. Intracellular Brucella species include classical and nonclassical types, with different species generally exhibiting host preferences. Some classical intracellular Brucella species can cause zoonotic brucellosis, including B. melitensis, B. abortus, B. suis, and B. canis. Extracellular Brucella species comprise opportunistic or environmental species which belonged formerly to the genus Ochrobactrum and thus nowadays renamed as for example Brucella intermedia or Brucella anthropi, which are the most frequent opportunistic human pathogens within the recently expanded genus Brucella. The cause of the diverse phenotypic characteristics of different Brucella species is still unclear. To further investigate the genetic evolutionary characteristics of the Brucella genus and elucidate the relationship between its genomic composition and prediction of phenotypic traits, we collected the genomic data of Brucella from the NCBI Genome database and conducted a comparative genomics study. We found that classical and nonclassical intracellular Brucella species and extracellular Brucella species exhibited differences in phylogenetic relationships, horizontal gene transfer and distribution patterns of mobile genetic elements, virulence factor genes, and antibiotic resistance genes, showing the close relationship between the genetic variations and prediction of phenotypic traits of different Brucella species. Furthermore, we found significant differences in horizontal gene transfer and the distribution patterns of mobile genetic elements, virulence factor genes, and antibiotic resistance genes between the two chromosomes of Brucella, indicating that the two chromosomes had distinct dynamics and plasticity and played different roles in the survival and evolution of Brucella. These findings provide new directions for exploring the genetic evolutionary characteristics of the Brucella genus and could offer new clues to elucidate the factors influencing the phenotypic diversity of the Brucella genus.

Evolution of the ability to evade host innate immune defense by Talaromyces marneffei.

Talaromyces (Penicillium) marneffei is an intracellular pathogenic fungus. Some strains of this fungus have been misidentified due to the similarity between Talaromyces and Penicillium. T. marneffei has mainly been found to afflict immunocompromised individuals, causing respiratory, skin, and systemic mycosis. Mp1p is a key virulence factor that can help T. marneffei evade clearance by the normally functioning immune system. Understanding how novel functions arise is an intriguing question in many fields of biology. Mp1p has two homologous domains (Mp1p-LBD1 and Mp1p-LBD2). Sequence similarity searches with Mp1p-LBD sequences revealed Mp1p homologs in many other pathogenic fungi. Integrated information on the taxonomic distribution, phylogenetic relationships, and sequence similarity of Mp1p domains revealed that the ancestor of Mp1p-LBDs was acquired through horizontal gene transfer (HGT). Additional evidence revealed that Mp1p homologs have undergone extensive gene duplications in T. marneffei. Mp1p might be a result of gene fusion following gene duplication. Furthermore, we propose a new method for identifying Talaromyces and identify 4 strains with misclassification errors. Our results characterize the evolutionary mechanism of T. marneffei evasion of host innate immune defense and clearly demonstrate the role of gene duplication and HGT in the evolution of host immune escape by T. marneffei.

Characterization and Diversity of Klebsiella pneumoniae Prophages.

Klebsiella pneumoniae is a common human commensal and opportunistic pathogen. In recent years, the clinical isolation and resistance rates of K. pneumoniae have shown a yearly increase, leading to a special interest in mobile genetic elements. Prophages are a representative class of mobile genetic elements that can carry host-friendly genes, transfer horizontally between strains, and coevolve with the host's genome. In this study, we identified 15,946 prophages from the genomes of 1437 fully assembled K. pneumoniae deposited in the NCBI database, with 9755 prophages on chromosomes and 6191 prophages on plasmids. We found prophages to be notably diverse and widely disseminated in the K. pneumoniae genomes. The K. pneumoniae prophages encoded multiple putative virulence factors and antibiotic resistance genes. The comparison of strain types with prophage types suggests that the two may be related. The differences in GC content between the same type of prophages and the genomic region in which they were located indicates the alien properties of the prophages. The overall distribution of GC content suggests that prophages integrated on chromosomes and plasmids may have different evolutionary characteristics. These results suggest a high prevalence of prophages in the K. pneumoniae genome and highlight the effect of prophages on strain characterization.