1.E.63. The Actinobacterial Phage Holin (AP-Holin) Family
A Streptomyces avermitilis bacteriophage, phiSASD1, expresses ORF40 and ORF19, predicted to be an endolysin (termed LytSD) and a holin (termed HolSD), respectively, two phage proteins involved in host lysis. The yield of LytSD was 17.2 mg per liter of culture. When applied exogenously, LytSD lysed 7/18 of the tested bacterial strains, including S. avermitilis, Bacillus subtilis, Staphylococcus aureus, Sarcina lutea, and Enterococcus faecalis. As regards HolSD, it resulted in growth inhibition of several tested strains and abrupt lysis of E. coli BL21 (DE3) pLysS. It complemented the defective λ S allele of non-suppressing E. coli strains to produce phage plaques. Thus, the functions of ORF40 and ORF19 of phage phiSASD1 are established (Lu et al. 2019).