Radiation Sensitivity ofHaemophilus influenzae:a Composite Response

Abstract

The survival of ultraviolet (UV)-irradiated cultures of Haemophilus influenzae Rd is determined by at least two responses: (i) excision-repair ability and (ii) UV-induced cell lysis. An UV-resistant mutant, BC200, has the same capabilities as the wild type, Rd, for excising dimers but does not exhibit lysis. Lytic response is dosedependent. Relative to the wild type, a lower dose of UV causes lysis of a UV-sensitive mutant, BCIOO, which is incapable of excising thymine dimers. A lytic protein is present in cultures undergoing lysis. Synthesis of this protein is initiated 45 to 60 min after irradiation. Lysis appears to be due to derepression of a defective prophage which codes for an endolysin-like lytic enzyme.

Repair of Single-Strand Deoxyribonucleic Acid Breaks in Ultraviolet Light-IrradiatedHaemophilus influenzae

“…UV-resistant mutant. The UV-resistant strain BC200 excises pyrimidine dimers at about the same rate as Rd (4). DNA sedimentation patterns determined for UV-irradiated BC200 are identical to those obtained for Rd at times shorter than 50 min.…”

“…UV-sensitive mutant. The UV-sensitive mutant BC100 does not excise pyrimidine dimers (4). No single-strand breaks can be detected in UV-irradiated samples of this mutant (Fig.…”

“…Increasing the number of dimers in DNA by increasing the UV dose might increase the chances of detecting breaks in DNA. Both BC200 and Rd excise more dimers during the first 60 min when irradiated with a dose of 300 ergs/mm2 than when irradiated with 125 ergs/ mm 2 (4). We thought also that, with the increased number of dimers, gaps might persist for a longer time at the higher dose.…”

“…4. A dose of 8 ergs/mm2 causes a maximum amount of cell lysis (80 to 90%) and permits about 5% of the cells to give rise to colonies on solid medium (4). Only the data obtained for samples incubated for 0, 20, and 50 min after UV irradiation are presented.…”

Restriction enzymes do not play a significant role in Haemophilus homospecific or heterospecific transformation

“…This integration causes the death of a considerable fraction of the recipient cells through induction of the defective prophage (29) that is present in the Rd strain used most widely (4,33). Since a presumably cured strain (2,4) is insensitive to this lethal effect and since heterospecific transformation is also normally inefficient in this strain (29), the prophage induction phenomenon is not believed to be the explanation for the reduced heterospecific transformation efficiency. The lowered marker transfer is thus probably caused by events that follow integration (for a thorough discussion, see reference 17).…”