Among the many early revelations from molecular phylogenetic studies of bacteria (Woese, 1987) was the recognition that the mycoplasmas represented a… - Nancy A. Moran

Symbioses are central in the evolution of complexity; have evolved many times and are critical to the lifestyles of many animals and plants and also to whole ecosystems, in which symbiotic organisms are key players. The primary reason that symbiosis research is suddenly active, after decades at the margins of mainstream biology, is that DNA technology and genomics give us enormous new ability to discover symbiont diversity, and more significantly, to reveal how microbial metabolic capabilities contribute to the functioning of hosts and biological communities.

The aphid Pemphigus betae typically shows a complex life cycle, with annual alternation between cottonwood trees, where it forms leaf galls, and herbaceous plants, where it lives on roots. Distinct phenotypes are associated with each phase. In a population in Utah, aphid clones vary in their tendencies to undergo the cottonwood phase of the life cycle, with certain clones rarely producing the winged migrants that initiate the cottonwood phase.

The guts of honey bee workers contain a distinctive community of bacterial species. They are microaerophilic or anaerobic, and were not clearly deliniated by earlier studies relying on laboratory culture of isolates under atmospheric oxygen levels. Recently, a more complete picture of the potential metabolism and functions of these bacteria have been possible, using genomic approaches based on metagenomic samples, as well as cultured isolates. Of these, most are host-restricted and are generally absent outside adult guts.