Summary
Most mycobacterial species spontaneously form biofilms, inducing unique growth physiologies and reducing drug sensitivity. Biofilm growth progresses through three genetically programmed stages: substratum attachment, intercellular aggregation and architecture maturation. Growth of Mycobacterium smegmatis biofilms requires multiple factors including a chaperonin (GroEL1) and a nucleoid-associated protein (Lsr2), although how their activities are linked remains unclear. Here we show that Lsr2 participates in intercellular aggregation, but substratum attachment of Lsr2 mutants is unaffected, thereby genetically distinguishing these developmental stages. Further, we identify a suppressor mutation in a glycopeptidolipid synthesis gene (mps) that results in hyperaggregation of cells and fully restores the form and functions of Δlsr2 mutant biofilms. Suppression by the mps mutation is specific to Δlsr2; it does not rescue the maturation-deficient biofilms of a ΔgroEL1 mutant, thereby differentiating the process of aggregation from maturation. Gene expression analysis supports a stepwise process of maturation, highlighted by temporally separated, transient inductions of iron and nitrogen import genes. Furthermore, GroEL1 activity is required for induction of nitrogen, but not iron, import genes. Together, our findings begin to define molecular checkpoints during development of mycobacterial biofilms.
SUMMARY
Eight mutant stocks of rats were typed for their histocompatibility (Ag‐B) and red cell (Ag‐C) antigens and were evaluated for their antibody responses to poly(Glu52Lys33Tyr15). The antibody responses were those predicted from the histocompatibility type, except for the B stock. These animals made a high antibody response, although their histocompatibility alleles were those normally associated with a low response.
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