Comparative genomics and metabolic model analysis of primary and secondary endosymbionts present in different species of whitefly.

Candidatus Portiera aleyrodidarum (hereafter Portiera) is the primary endosymbiont of whiteflies (Hemiptera: Aleyrodidae), residing in specialized bacteriocytes that also co-localize diverse secondary endosymbionts. This study aimed to carry out in-depth genomic analysis of different strains of Portiera and secondary endosymbionts namely Arsenophonus, Cardinium, Hamiltonella, Rickettsia, and Wolbachia obtained from different whitefly species (data obtained from NCBI). Interestingly, hierarchical clustering of the amino acid identity data resulted in a dendrogram that resolved the different strains of Portiera into 3 separate genetic clusters. Pan-genome analysis of endosymbionts indicates that even closely related strains of a species, when isolated from different hosts, show unique genomic compositions due to their capability to adapt to a specific environment. COG/KEGG analysis revealed that amino acid metabolism is second most represented functional category of Portiera genomes whereas it is almost negligible in genomic repertoire of secondary endosymbionts except in Hamiltonella. Biosynthetic pathway analysis shows that threonine is the only essential amino acid for which complete set of genes is present in all strains of Portiera followed by leucine and tryptophan which is synthesized by all except 1 (China) and 2 strains (AD-CAI and SiSi), respectively. However, both amino acid lysine and arginine could be synthesized by only 4 strains namely AD-CAI, AF-CAI, PeMo, and TV. Further, the study established that secondary endosymbionts are capable of enriching the host's diet with protective organic compounds, B vitamins, and cofactors which is in contrast to the role of Portiera. Results of pathway-specific metabolic modelling were highly congruent with KEGG pathway predictions, depicting a positive correlation between the genotype and phenotype of endosymbionts.