AUTHOR=Bukka Archana , Price Christopher T., Kernodle Douglas S., Graham James E.

TITLE=Mycobacterium tuberculosis RNA Expression Patterns in Sputum Bacteria Indicate Secreted Esx Factors Contributing to Growth are Highly Expressed in Active Disease

JOURNAL=Frontiers in Microbiology

VOLUME=volume 2 - 2011

YEAR=2012

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2011.00266

DOI=10.3389/fmicb.2011.00266

ISSN=1664-302X

ABSTRACT=To identify factors contributing to the ability of tubercle bacilli to grow in the lung during active infection, we analyzed RNA expression patterns in bacteria present in patient sputum. Prominent among bacterial transcripts identified were those encoding secreted peptides of the Esat-6 subfamily that includes EsxK and EsxL (Rv1197 and Rv1198). H37Rv esxKL and esxJI transcripts were differentially expressed under different growth conditions, and disruption of these genes altered growth phase kinetics in typical laboratory batch broth cultures. These growth defects, including the reduced intracellular growth of an ΔesxKL mutant in primary human macrophages, were reversed by either low multiplicity co-infection or co-culture with wild-type bacteria, demonstrating the ability of the secreted factors to rescue isogenic mutants. Complementing either only esxL or esxI alone (Rv1198 or Rv1037c) also reduced observed growth defects, indicating these genes encode factors capable of contributing to growth. Our studies indicate that the M. tuberculosis Mtb9.9 family secreted factors EsxL and EsxI can act in trans to modulate growth of intracellular bacteria, and are highly expressed during active human lung infection. EsxL (Rv1197 and Rv1198). The H37Rv genome contains 4 additional and nearly identical pairs of co-linear open reading frames designated esx JI, esx MN, esx PO, and esxWV. These ORFs show little sequence similarity to esxBA (Cfp10-Esat-6), other than encoding 2 short ~100 residue peptides with the 5’ ORF encoding a variant carboxyl-terminal 'QILSS' motif and the 3’ encoding the Mtb9.9 family of secreted T-cell antigens. All contain a central ‘WXG100’ esx family structural motif, and are thought to encode effectors of an uncharacterized ESX-5 transport system. esxKL and esxJI transcripts were differentially expressed under different growth conditions, and disruption of these genes altered different growth phase kinetics in typical laboratory batch broth cultures.