NONPHOTOREACTIVATING REPAIR OF ULTRAVIOLET LIGHT-DAMAGED MICROCOCCUS LYSODEIKTICUS CELLS

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Micrococcus lysodeikticus cells display remarkable resistance to ultraviolet (UV) radiation.
• The dose-survival curve suggests an inherent repair mechanism within these cells.
• Photoreactivation, a light-dependent repair pathway, is not observed in M. lysodeikticus.

Purpose of the Study:

• To investigate the nature of the UV resistance in Micrococcus lysodeikticus.
• To identify and characterize the repair mechanisms involved in UV damage.
• To determine the effect of specific inhibitors on UV resistance and survival.

Main Methods:

• UV irradiation of Micrococcus lysodeikticus cells.
• Treatment with dinitrophenol and iodoacetate before and after UV exposure.
• Analysis of dose-survival curves and lag phases.
• Testing UV-radiated phage inactivation on treated host cells.

Main Results:

• Dinitrophenol and iodoacetate significantly reduced survival rates and altered the dose-kill curve when applied pre- or post-irradiation.
• The inhibitory effect of these compounds was dependent on time and temperature.
• Surviving cells exhibited a prolonged lag phase before resuming multiplication.
• UV-radiated phage showed increased inactivation on M. lysodeikticus treated with dinitrophenol.

Conclusions:

• The resistance of M. lysodeikticus to UV radiation is attributed to a highly effective dark-cell repair mechanism.
• This dark repair pathway can be effectively blocked by chemical inhibitors like iodoacetate and dinitrophenol.
• The findings highlight the importance of dark repair in bacterial UV resistance.