The photosynthetic purple bacterium Thermochromatium (Tch.)tepidumis a thermophile that grows at an optimal temperatureof ∼50 °C. We have investigated, by means of steady-stateand time-resolved optical spectroscopies, the effects of temperatureon the near-infrared light absorption and the excitation energy transfer(EET) dynamics of its light-harvesting complex 2 (LH2), for whichthe mesophilic counterpart of Rhodobacter(Rba.) sphaeroides2.4.1 (∼30 °C)was examined in comparison. In a limited range around the physiologicaltemperature (10–55 °C), the B800-to-B850 EET process ofthe Tch. tepidumLH2, but not the Rba. sphaeroidesLH2, was found to be characteristically temperature-dependent, mainlybecause of a temperature-tunable spectral overlap. At 55 °C,the LH2 complex from Tch. tepidummaintained efficientnear-infrared light harvesting and B800-to-B850 EET dynamics, whereasthis EET process was disrupted in the case of Rba. sphaeroides2.4.1 owing to the structural distortion of the LH2 complex. Ourresults reveal a remarkable thermal adaptability of the light-harvestingfunction of Tch. tepidum, which could enhance ourunderstanding of the survival strategy of this thermophile in responseto environmental challenges. [ABSTRACT FROM AUTHOR]