PHOTOKILLING OF MICROCOCCUS ROSEUS

Abstract

Abstract. Previous work showed that the bacterium Micrococcus roseus is killed by photodynamic action when an exogenous photosensitizer is present, but when a photosensitizer is not added the organism survives long exposure to high intensity (22,000ft‐c, 348 J/s/m2) white light. Experiments designed to demonstrate the presence of a mechanism to repair damage caused by photodynamic action failed to reveal such a mechanism. However, the organism was killed by light of a very high intensity (32,000ft‐c, 506 J/s/m2) in the absence of added photosensitizer, indicating that cells have an effective endogenous photosensitizer(s). Two carotenoid‐deficient mutants were killed via photodynamic action more rapidly than the fully pigmented wild‐type in the presence or absence of an exogenous photosensitizer. Thus, resistance of M. roseus to photodynamic action is not due to a repair mechanism, nor to lack of an effective endogenous photosensitizer, but to the protective action of carotenoid pigments.

The relationship between carotenoids and sunlight response in members of the family Micrococcaceae

“…Radiation effects observed in Micrococcus using toluidine blue as an exogenous photosensitizer are not comparable with the results presented here [25]. In Myxococcus xanthus carotenoid functions are related with an unusual accumulation of porphyrin [5], and in Micrococcus roseus ATCC 516 [6], at present classified as Kocuria rosea [19], photoprotection is provided by canthaxanthin, echinenone, 4-hydroxyechinenone, and other pigments with a β,β-carotene structure [26], which are structurally different from those found in RMB40. Sarcina lutea ATCC 9341 [3,4] was classified as Micrococcus luteus in 1977, but it was re-classified as Kocuria rhizophila in 2003 [27] and its pigments have not been characterized.…”