Mechanisms of bacteriophage inactivation via singlet oxygen generation in UV illuminated fullerol suspensions

Nonenveloped viruses are shown to be inactivated by singlet oxygen ((1)O2) produced in UVA photosensitized aqueous suspensions of a polyhydroxylated fullerene (C60(OH)22-24; fullerol, 40 microM). Experiments were performed with MS2, a ssRNA bacteriophage, as well as two dsDNA phages: PRD1, which has an internal lipid membrane, and T7, which entirely lacks lipids. MS2 was highly susceptible to inactivation, having a rate constant of 0.034 min(-1) with UVA alone, which increased to 0.102 min(-1) with photoactivated fullerol. PRD1 and T7 were not susceptible to UVA alone but were photoinactivated by fullerol with rate constants of 0.026 and 0.035 min(-1), respectively. The role of 1(O)2 was demonstrated by three independent observations: (i) viruses that were insensitive to UVA alone were photoinactivated by rose bengal in the absence of fullerol, (ii) beta-carotene reduced (but did not eliminate) photoinactivation rates, and (iii) singlet oxygen sensor green fluorescence spectroscopy directly detected (1)O2 in UVA illuminated fullerol suspensions. Qualitative evidence is also presented that fullerol aggregates were closely associated with viruses allowing efficient transfer of 1(O)2 to their capsids. Fourier transform infrared spectroscopy revealed significant oxidative modifications to capsid proteins but comparatively minor changes to the DNA and (phospho)lipids. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) suggested (1)O2 induced crosslinking of proteins. Hence, phage inactivation by photoactivated fullerol nanoparticles appears to be caused by cross-linking of capsid protein secondary structures by exogenous (1)O2 and consequentimpairmentof their ability to bind to surface receptors of their bacterial hosts (loss of infectivity) rather than by direct reactions with fullerol.