Stress is the rule rather than the exception for Metarhizium

The insect pathogenic plant root symbiont Metarhizium experiences many situations that restrict its growth whether living in host insects or on plant roots. These include a range of physical, chemical and biological effects involving UV and extremes of temperature, pH, nutrient availability, toxic metals and other pollutants, and insect host defenses such as production of reactive oxygen species. Aside virulence, the major impediment to reliable pest control with Metarhizium is its sensitivity to UV and temperature extremes. However, increased levels of stress tolerance can be engineered into Metarhizium quite simply by reprogramming the expression of single downstream endogenous genes. For example, overexpression of RNA-binding proteins resulted in Metarhizium with increased tolerance to cold stress, overexpression of photolyase increased tolerance to UV, and increased expression of heat shock protein 25 improved tolerance to several stress conditions, including heat, and osmotic pressure. Conversely, disruption of these genes greatly reduced persistence, and could provide genetic containment for genetically engineered hypervirulent strains.