Horizontal Acquisition and Transcriptional Integration of Novel Genes in Mosquito-Associated Spiroplasma

Abstract

Genetic differentiation among symbiotic bacteria is important in shaping biodiversity. The genus Spiroplasma contains species occupying diverse niches and is a model system for symbiont evolution. Previous studies have established that two mosquito-associated species have diverged extensively in their carbohydrate metabolism genes despite having a close phylogenetic relationship. Notably, although the commensal Spiroplasma diminutum lacks identifiable pathogenicity factors, the pathogenic Spiroplasma taiwanense was found to have acquired a virulence factor glpO and its associated genes through horizontal transfer. However, it is unclear if these acquired genes have been integrated into the regulatory network. In this study, we inferred the gene content evolution in these bacteria, as well as examined their transcriptomes in response to glucose availability. The results indicated that both species have many more gene acquisitions from the Mycoides-Entomoplasmataceae clade, which contains several important pathogens of ruminants, than previously thought. Moreover, several acquired genes have higher expression levels than the vertically inherited homologs, indicating possible functional replacement. Finally, the virulence factor and its functionally linked genes in S. taiwanense were up-regulated in response to glucose starvation, suggesting that these acquired genes are under expression regulation and the pathogenicity may be a stress response. In summary, although differential gene losses are a major process for symbiont divergence, gene gains are critical in counteracting genome degradation and driving diversification among facultative symbionts.

Horizontal Gene Acquisitions Contributed to Genome Expansion in Insect-Symbiotic Spiroplasma clarkii

“…2004 ; Regassa and Gasparich 2006 ; Gasparich 2010 ; Gasparich 2014 ), this overlap in ecological niche could have promoted the HGT events among these lineages. Moreover, despite the phylogenetic divergence, all these Mollicutes lineages share the same alternative genetic code (i.e., UGA changed from stop to tryptophan) and a strong nucleotide composition bias toward A + T. These shared genomic traits could have promoted the retention and integration of those acquired genes ( Lo and Kuo 2017 ). The chromosomal region at ∼0.9–1.1 Mb appeared to be the major hot spot for foreign genes ( fig.…”

“…2015 ) and is important in their physiology and ecology ( Regassa and Gasparich 2006 ; Gasparich 2010 ). Moreover, carbohydrate metabolism genes are often involved in HGT and have been shown to be integrated into the gene expression regulation in other Apis clade species ( Lo and Kuo 2017 ). Intriguingly, extensive gene acquisition has also been reported for Spiroplasma eriocheiris of the Mirum clade, in which ∼7% of the genes may be acquired from non- Spiroplasma donors ( Lo et al.…”

Convergent Evolution among Ruminant-Pathogenic Mycoplasma Involved Extensive Gene Content Changes

“…2013 ; Lo et al. 2013 ; Lo and Kuo 2017 ). Briefly, the amino acid sequences of conserved single-copy genes were aligned using MUSCLE v3.8 ( Edgar 2004 ).…”

Redundancy and Specificity of Type VI Secretion vgrG Loci in Antibacterial Activity of Agrobacterium tumefaciens 1D1609 Strain

“…After genome selection, the procedures for homologous gene identification and molecular phylogenetic analysis were based on those described in our previous studies (Lo et al, 2013;Lo and Kuo, 2017). Briefly, the homologous genes among all genomes were identified by using OrthoMCL (Li et al, 2003).…”