**6. Timing of responses to acidity**

There seems to be a difference in the timing of upregulation of genes involved in response to acidic stress. At 15-30 minutes a number of genes are upregulated and this seems to constitute an immediate response. This early response may be controlled by VirsS at least for the *mymA* operon as previously described (Singh et al; 2005). The *lipF* promoter part of the PhoP regulon, failed to be identified as upregulated by acidic stress at 15-30 minutes (Fisher et al; 2002). However, this promoter is upregulated after 1.5 hour, with maximum regulation occurring after 24 hours (Saviola et al; 2002). At 2 hours 24 of 44 known PhoP genes are upregulated in macrophages (Rohde et al; 2007). An even later response occurs that results in the accumulation of triacylglycerol that *M. tuberculosis* may need for long term survival under stress. Tgs1 is implicated in triacylglycerol storage and when this gene is deleted the mutant fails to accumulate triacylglycerol within mycobacterial cells. Tgs1 was not upregulated at 15 minutes by acidic shock (Fisher et al; 2002). It was however upregulated upon extended acidic conditions of 3 weeks duration (Sirakova et al; 2006, Low et al; 2009, Deb et al; 2009). Thus there are varying time frames for the response to acidic conditions. There may not be 3 discrete times, but a multitude of response times. Distinct time frames of response to acidity may correlate with transcriptional regulators which

Response of Mycobacterial Species to an Acidic Environment 99

Brown BA, Springer VA, Steingrube RW, Wilson GE, Pfyffer MJ, Garcia MC, Menendez B,

Buchmeier N, Blanc-Potard A, Ehrt S, Piddington D, Riley L,and Groisman EA.2000. A

Camacho LR, Ensergueix D, Perez E, Gicquel B, Guilhot C. 1991 Identification of a virulence

Chapman JS and Bernard JS. The tolerances of unclassified mycobacteria. I. Limits of pH

Chesne-Seck M, Barilone N, Boudou F, Asensio JG, Kolattukudy PE, Martin C, Cole ST,

Dannenberg AM (2006) Pathogenesis of Human Pulmonary Tuberculosis: Insights from the

Deb C, Lee CM, Dubey VS, Daniel J, Abomoelak B, Sirakova S, Pawar S, Rogers L,

Ehrt S, and Schnappinger D. 2009. Mycobacterial survival strategies in the phagosome: defence against host stresses. Cellular Microbiology. 11(8):1170-1178. Fisher MA, Plikayatis BB,and Scinnick TM. 2002. Microarray of the *Mycobacterium* 

Frigui W, Bottai D, Majlessi L, Monot M, Josselin E, Brodin P, Garnier T, Gicquel B, Martin

secretion and specific T cell recognition by PhoP. PLOS Pathogens. 4:e22. Gonzalo-Asensio J, Mostowy S, Harders-Westerveen J, Huygen K, Hernandez-Pando R,

Hoffmann C, Leis A, Niederweis M, Plitzko JM, and Engelhardt H. 2008. structure.

Huynh KK, and Grinstein S. 2007. Regulation of vacuolar pH and its modulation by some microbial species. Micobiology and molecular biology reviews. 71(3):452-462. Kim S, Lee B, Shin SJ, Kim H, and Park J. 2008. Differentially expressed genes in

regulatory region of the promoter. FEBS Letters. 580:5328-5338.

Proceedings of the National Academy of Science.105(10):3963-7.

*tuberculosis* transcriptional response to the acidic conditions found in phagososmes.

C, Leclerc C, Cole ST, and Brosch R. 2008. Control of M. tuberculosis Esat-6

Thole J, Behr M, Gicquel B, and Martin C. 2008. PhoP: a missing piece in the intricate puzzle of *Mycobacterium tuberculosis* virulence. Plos One. 3(10):e3496. Gupta S, Sinha A, and Sarkar D. 2006. Transcriptional autoregulation by *Mycobacterium* 

*tuberculosis* PhoP involves recognition of novel direct repeat sequences in the

*Mycobacterium tuberculosis* H37Rv under mild acidic and hypoxic conditions.

and *Salmonella enterica*. Molecular Microbiology. 35(6):1375-1382.

tolerance. American Review of Respiratory Disease. 86:582-583.

*tuberculosis* H37Ra.Journal of Bacteriology. 190(4):1329-1334.

Bacteriology. 49:143-151.

Molecular Microbiology. 32:257-267.

Rabbit Model. ASM Press, Washington, DC.

Kolattukudy PE. 2009. Plos One 4(6):e6077.

Journal of Bacteriology. 184(14): 4025-4032.

Journal of medical Microbiology. 57:1473-1480.

Rodriguez-Salgado KC, Jost Jr SH, Chiu SH, Onyi GO, Bottger EC, and Wallace RJ. 1999. *Mycobacterium wolinski* sp nov. and *Mycobacterium goodii* sp. nov. Two New Rapidly Growing Species Related to *Mycobacterium smegmatis* and Associated with Human Wound Infections: a Cooperative Study from the International Working Group on Mycobacterial Taxonomy . International Journal of Systematic

parallel intraphagosomal survival strategy shared by *Mycobacterium tuberculosis* 

cluster of *Mycobacterium tuberculosis* by signature-tagged transposon mutagenesis.

Gicquel B, Gopaul DN, and Jackson M. 2008. A point mutation in the twocomponent regulator PhoP-PhoR accounts for the absence of polyketide-derived acyltrehaloses but not that of phthiocerol dimycocerates in *Mycobacterium* 

control acid responsive genes. The kinetics of the response will be different for each regulator and as a consequence depend on the exact nature of the signal that the regulator senses. Signals may be a direct or indirect consequence of acidic damage. These questions will be important when considering acid responsive genes as drug targets. Inhibition of a gene expressed early may block establishment of infection but be ineffective during chronic infection. Likewise a drug against a gene upregulated at 3 weeks may be effective against a chronic infection but be unable to prevent establishment of infection.
