Search

Mycobacterium tuberculosis and the closely related organism Mycobacterium bovis can survive and replicate inside macrophages. Intracellular survival is at least in part attributed to the failure of mycobacterial phagosomes to undergo fusion with lysosomes. The transformation of phagosomes into phagolysosomes involves gradual acquisition of markers from the endosomal compartment. Members of the rab family of small GTPases which confer fusion competence in the endocytic pathway are exchanged sequentially onto the phagosomal membranes in the course of their maturation. To identify the step at which the fusion capability of phagosomes containing mycobacteria is compromised, we purified green fluorescent protein-labeled M. bovis BCG phagosomal compartments (MPC) and compared GTP-binding protein profiles of these vesicles with latex bead phagosomal compartments (LBC). We report that the MPC do not acquire rab7, specific for late endosomes, even 7 days postinfection, whereas this GTP-binding protein is present on the LBC within hours after phagocytosis. By contrast, rab5 is retained and enriched with time on the MPC, suggesting fusion competence with an early endosomal compartment. Prior infection of macrophages with M. bovis BCG also affected the dynamics of rab5 and rab7 acquisition by subsequently formed LBC. Selective exclusion of rab7, coupled with the retention of rab5 on the mycobacterial phagosome, may allow organisms from the M. tuberculosis complex to avert the usual physiological destination of phagocytosed material.

Since water conditions could well decide whether the 5000-psi 1200-F Eddystone unit could be operated satisfactorily, every condition which might lead to a problem was given careful consideration. Tests at supercritical pressure indicated that a considerable amount of “soluble salts” deposited in the 850 to 950-F range when initially present at 2.0 ppm. Less deposition occurred with potassium salts than with sodium, but it was sufficient to make careful control of solids in the whole system imperative. This will be accomplished by demineralization of the make-up and by bypass demineralization of condensate as required. When present in the amount anticipated for Eddystone, even at 1200 F there was no measurable decomposition or deposition of salts. As to corrosion, proper control of dissolved oxygen and maintaining 10-ppb hydrazine and sufficient ammonia to give an 8.5 to 9.5 pH range, insured low metal pickup. Thus, deposition of metallic oxides in the boiler and turbine does not appear to be a problem. Corrosion tests and metallographic examination of the various alloys used indicate no harmful loss of metal or change in structure, hence no service-life problems are expected.