Final answer:
Many environmental microbes are unculturable in lab settings due to highly specific and often unknown growth requirements, and some present potential biohazards. Obligate intracellular parasites can't be cultured outside host cells, and certain microbes adapted to extreme conditions may not thrive in a lab.
Step-by-step explanation:
Many environmental microbes cannot be cultured in the laboratory due to highly specific and often unknown nutritional and environmental requirements. Over 99 percent of bacteria and archaea remain unculturable for reasons including unknown needs for specific micronutrients, pH, temperature, pressure, co-factors, or co-metabolites. Moreover, some bacteria are obligate intracellular parasites, requiring a host cell to grow, which cannot be easily replicated in a lab setting.
Additionally, the task of culturing microbes can be hindered by the potential danger they pose as some are exotic and could cause aerosol-transmitted infections. This necessitates a high level of biosecurity, which few labs possess. Lastly, extreme environmental conditions can challenge microbial life on Earth and microbes adapted to such conditions may not thrive when removed from those specific contexts.