authors request that the following clarification be noted. The Methods and Materials on p. 6987, line 28, indicated that mycobacterial cultures were grown in Middlebrook 7H9 broth (Difco) supplemented with ADC (albumin-dextrose complex) and 0.05% Tween 80. Middlebrook broth as originally formulated (23) and subsequently used for mycobacteria (24) contains glycerol. It has been brought to the authors' attention that the label on the Middlebrook-Dubos medium currently supplied by Difco states "if desired [each liter may contain] 2 ml glycerol or 0.05% Tween" (italics added). For the purposes of genetic transformation of BCG, the authors find that inclusion of 0.2% glycerol, as in the standard formulation, is required.

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Wall-deficient forms of fast-growing mycobacteria were produced in growth medium containing vancomycin and glycine, and spheroplasts were prepared by lysozyme treatment of wall-deficient cells. Spheroplasts gave rise to recombinants with high frequency (2-6 %) when they were fused using polyethylene glycol 6000. The results demonstrated that in uivo genetic recombination could be used to produce genetically modified Mycobacterium strains with applications in transformation of steroids. Useful intermediates of steroid drug synthesis and new degradation products were obtained from sterols by selected recombinant strains.

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