Genomic insights into symbiosis and host adaptation of an ascidian-associated bacterium Bacillus aryabhattai MCCB 387

• Published in: Symbiosis (Philadelphia, Pa.) Vol. 87; no. 2; pp. 129 - 142
• Main Authors: Merlin, Titus Susan, Umar, Md, Puthiyedathu, Sajeevan Thavarool
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-06-2022; Springer Nature B.V
• Subjects: Bacillus aryabhattai; Biomedical and Life Sciences; Colonization; CRISPR; Developmental Biology; Ecology; Evolutionary Biology; Fibronectin; Gene clusters; Gene transfer; Genomes; Genomics; Horizontal transfer; Integrins; Life Sciences; Microbiology; Plant Sciences; Reproductive fitness; Restriction-modification; Symbiosis; Symbiosis; Genomic features; Niche; Ascidian; Horizontal gene transfer
• ISSN: 0334-5114; 1878-7665
• DOI: 10.1007/s13199-022-00860-1

Ascidians are a highly evolved invertebrate group enjoying a wide global distribution and are well known for their symbiotic association with microbial communities. Here, we analysed the genomic features of an ascidian associated bacterium,
Bacillus aryabhattai
MCCB 387 and compared its genomic features with the other three free-living
B. aryabhattai
reported from different ecological niches to underpin the gene repertoires involved in successful colonisation and symbiosis. In general, many ‘symbiosis factors’ genes have been observed in all four isolates demonstrating their potential to live with eukaryotic hosts. However, ascidian-associated
B. aryabhattai
MCCB 387 showed certain additional and unique features and metabolic specificity, which might have favoured and enhanced the ecological fitness of a host association. On detailed analysis, the gene for fibronectin proteins which helps to bind with integrins and facilitate cell–cell contact and possible colonisation is seen in ascidian-associated 
B. aryabhattai
 MCCB 387. The presence of one complete set of CRISPR-Cas region, Type I restriction-modification system and Toxin-antitoxin systems in MCCB 387 shows the genomic features favouring the symbiotic mode of life. MCCB 387 genome revealed a comparatively high number of Biosynthetic Gene Clusters (smBGCs) supporting the strain's secondary metabolite production potential, which might enhance fitness toward host-symbiont interaction. The genome of
B. aryabhattai
MCCB 387 is enriched with Mobile Genetic Elements (MGEs), suggestive of increased horizontal gene transfer between the host-microbial communities. Enriched MGEs might contribute to acquiring new genetic features and genome plasticity for the symbiont. Taken together, these genomic features might confer
B. aryabhattai
MCCB 387 an edge over other potential competitors, which likely enhances its ecological fitness and host colonisation.