Bayer and Ginkgo Bioworks are forming a company to exploit the potential of synthetic biology to improve microbes that help plants grow. The as yet unnamed firm launches with a $100 million investment from the parent companies and Viking Global Investors. Plants such as soybeans, peas, and peanuts benefit from symbiotic microbes that fix nitrogen from the air and make it available to plant roots. The new company seeks to boost the abilities of these microbes. It will be based at Gingko’s Boston labs and the West Sacramento, Calif., home of Bayer’s plant biologic activities.