Microorganisms which grow at moderate temperatures in the range 20-45 °C, and which have an optimum growth temperature in the range 30-39 °C.
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 160 (https://doi.org/10.1351/pac199264010143)