Genome evolution following an ecological shift in nectar-dwelling <i>Acinetobacter</i>

Many bacteria, including the genus <i>Acinetobacter</i>, commonly evolve to exploit new habitats. However, the genetic changes that underlie habitat switches are often unknown. Floral nectar is home to specialized microbes that can grow in this nutritionally unbalanced habitat. Several specialized <i>Acinetobacter</i> species evolved from soil-dwelling relatives to become common and abundant in floral nectar. Here, we investigate the genomic adaptations required to successfully colonize a novel habitat like floral nectar. We performed comparative genomics analyses between nectar-dwelling <i>Acinetobacter</i> and <i>Acinetobacter</i> species from other environments, like soil and water. We find that although gene loss coincided with the switch to living in nectar, gains of specific genes from other bacteria may have been particularly important for this ecological change. <i>Acinetobacter</i> living in nectar gained genes for degrading pectin, a plant polysaccharide, which may improve access to nutrients in their environment. These findings shed light on how evolutionary novelty evolves in bacteria.