Final answer:
Bacteria B needs threonine, leucine, and thiamine to grow, as indicated by the 'thr-', 'leu-', and 'thi-' markers. These terms signify that it cannot produce these compounds on its own and must obtain them from its environment. Such nutrients are part of the necessary supplements some bacteria need for growth.
Step-by-step explanation:
Bacteria B is "thr-", "leu-" and "thi-" which means it needs threonine, leucine, and thiamine to grow. These terms indicate that the bacteria are auxotrophic for these compounds, meaning they cannot synthesize them on their own and must obtain them from their environment. In the context provided, when bacteria strains A and B are incubated together in a medium containing each supplement, they can provide each other with the necessary growth factors.
Hence, when transferred to a minimal medium without supplements, each strain can still grow because they have shared metabolic capabilities that compensate for their individual auxotrophies. Bacteria, in general, require macronutrients and micronutrients, which include carbon, hydrogen, nitrogen, phosphorus, sulfur, and metallic elements, for growth and enzyme function. Some bacteria also require additional supplements, such as vitamins or other growth factors.