Lamichhane, Gyanu

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Frontiers in Cellular and Infection Microbiology

Mycobacterium tuberculosis response to stress from reactive oxygen and nitrogen species

Gyanu Lamichhane

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Frontiers in Microbiology

Mycobacterium Tuberculosis Response to Stress from Reactive Oxygen and Nitrogen Species

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Mycobacterium tuberculosis response to stress from reactive 
oxygen and nitrogen species
Gyanu Lamichhane*
Center for Tuberculosis Research, Department of Medicine, Johns Hopkins University, Baltimore, MD, USA
*Correspondence: lamichhane@jhu.edu
A commentary on
The response of Mycobacterium tuberculo-
sis to reactive oxygen and nitrogen species
by Voskuil, M. I., Bartek, I. L., Visconti, K., 
and Schoolnik, G. K. (2011). Front. Microbiol. 
2:105. doi: 10.3389/fmicb.2011.00105
The infectious life cycle of Mycobacterium 
tuberculosis (Mtb), as it relates to the dis-
ease tuberculosis (TB) in humans, begins 
from release of the bacilli in fine aerosol 
particles when an individual with active 
TB coughs or sneezes. When these bacilli 
are inhaled and reach the alveolar spaces of 
the lungs, they are ingested by phagocytic 
cells, primarily the macrophages. It is within 
the macrophages and also extracellularly 
during early and late stages of disease that 
Mtb has to thrive. The ability to survive is a 
prerequisite for Mtb to maintain infection 
without causing clinical disease, a condi-
tion known as “latent infection” that has 
allowed Mtb to maintain its reservoir in an 
estimated 2 billion humans (Jasmer et al., 
2002). The ability to proliferate, both intra-
cellularly and extracellularly is a prerequi-
site to cause active TB. Although majority 
of TB is pulmonary, Mtb can disseminate to 
and infect most organs and tissues causing 
a variety of TB diseases.
The host mounts a complex response to 
kill Mtb or limit its proliferation. Reactive 
oxygen and nitrogen intermediates have 
been widely reported and demonstrated 
as major antimicrobial molecules pro-
duced by the host (Nathan and Ehrt, 
2004). Expression of nitric oxide syn-
thase and markers associated with nitric 
oxide were observed to be expressed at 
elevated levels in the tuberculous lesion 
of lungs obtained from TB patients (Choi 
et al., 2002). Macrophages constitute a 
major host defense against Mtb infection; 
activated macrophages use nitric oxide 
against Mtb to kill or suppress its multi-
plication (Ehrt et al., 2001; Nathan and 
Ehrt, 2004). Macrophages obtained from 
now widely known as the “Mtb dormancy 
regulon” mediates physiological transition 
and adaptation to dormancy.
Voskuil et al. (2011) recently under-
took an exhaustive study to profile whole 
genome expression in response to oxidative 
and nitrosative stresses. Hydrogen peroxide 
(H
2
O
2
) and diethylenetriamine–nitric oxide 
adduct (DETA/NO) where used as donors 
of reactive oxygen and nitrogen intermedi-
ates respectively in an otherwise nutrient 
rich broth. Total RNA isolated from Mtb 
exposed to defined but a wide range of 
concentrations of H
2
O
2
 or NO donors were 
compared using oligonucleotide microar-
rays representing all genes of Mtb. This is 
an exhaustive approach and yielded a more 
comprehensive list of stress-responsive 
genes than earlier studies. Expressions of a 
majority of the genes in the dormancy regu-
lon were enhanced at low concentrations 
of NO (0.05 mM DETA/NO) but without 
affecting growth of Mtb. At higher concen-
trations, numerous genes but with func-
tions related to oxidative stress were also 
induced concurrently with the dormancy 
regulon.
The transcriptional response of Mtb to 
oxidative stress from H
2
O
2
, had similari-
ties and differences compared to NO stress, 
revealing common and unique responses 
used by the bacteria against these stresses. 
The genes involved in DNA repair and 
recombination were selectively induced 
in the presence of H
2
O
2
. This suggests that 
DNA damage is a significant consequence 
following exposure to H
2
O
2
. Despite this 
significant insult on DNA, Mtb tolerated as 
high as 10 mM H
2
O
2
. Also induced by H
2
O
2
 
exposure were several genes of PE and PPE 
family. Although this gene family makes up 
as much as 9% of the Mtb genome (Cole 
et al., 1998), their functions remain largely 
unknown.
Notably, this study revealed a common 
genetic apparatus used by Mtb to respond 
to oxidative and nitrosative stresses. Genes 
that encode functions related to general 
 bronchoalveolar lavages of TB patients 
and not from healthy individuals actively 
express nitric oxide synthase (Nicholson 
et al., 1996). Although the mouse model of 
TB does not fully recapitulate pathogenesis 
of TB and host response in humans, it has 
provided numerous lines of evidences sug-
gesting a significant role of nitric oxide in 
limiting Mtb infection. Mice lacking nitric 
oxide synthase 2 are considerably more sus-
ceptible to Mtb infection than the parent 
wild-type strain (MacMicking et al., 1997). 
Activated macrophages that express nitric 
oxide synthase kill Mtb but this activity is 
lost in the presence of nitric oxide synthase 
inhibitors (Chan et al., 1992). The litera-
ture is less rich in its description of role of 
reactive oxygen species in TB. A transient 
attenuated response against Mtb infection 
in the absence of phox gene responsible for 
generating reactive oxygen species has been 
reported from a study that used mouse as 
the host (Cooper et al., 2000). However, the 
significance of reactive oxygen species in 
TB in humans and mechanism of action 
has yet to be confirmed. Two loci in the 
genome of Mtb have been recently identi-
fied and attributed to be involved in defense 
against host generated (Cirillo et al., 2009; 
Colangeli et al., 2009).
The molecular mechanism of action of 
nitric oxide is not fully understood although 
it has been shown to inhibit aerobic res-
piration in mitochondria as well (Brown, 
2001). The Schoolnik laboratory has main-
tained a productive effort in understand-
ing the effect of nitric oxide intermediates 
on Mtb and the pathogen’s response to 
it. In 2003, Schnappinger and colleagues 
reported presence of physiologically sig-
nificant oxidative and nitrosative stresses 
in macrophage phagosomes harboring Mtb 
(Schnappinger et al., 2003). Simultaneously, 
Voskuil et al. (2003) reported inhibition of 
respiration and growth of Mtb by nitric 
oxide. In addition, this study also identi-
fied a regulon comprising 48 genes that is 
modulated by nitric oxide. This regulon, 
www.frontiersin.org August 2011 | Volume 2 | Article 176 | 1
General Commentary
published: 27 August 2011
doi: 10.3389/fmicb.2011.00176
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Voskuil, M. I., Bartek, I. L., Visconti, K., and Schoolnik, 
G. K. (2011). The response of Mycobacterium tuber-
culosis to reactive oxygen and nitrogen species. Front. 
Microbiol. 2:105. doi: 10.3389/fmicb.2011.00105
Voskuil, M. I., Schnappinger, D., Visconti, K. C., Harrell, 
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Received: 23 July 2011; accepted: 09 August 2011; published 
online: 27 August 2011.
Citation: Lamichhane G (2011) Mycobacterium tuberculo-
sis response to stress from reactive oxygen and nitrogen spe-
cies. Front. Microbio. 2:176. doi: 10.3389/fmicb.2011.00176
This article was submitted to Frontiers in Cellular 
and Infection Microbiology, a specialty of Frontiers in 
Microbiology.
Copyright © 2011 Lamichhane. This is an open-access arti-
cle subject to a non-exclusive license between the authors 
and Frontiers Media SA, which permits use, distribution 
and reproduction in other forums, provided the original 
authors and source are credited and other Frontiers condi-
tions are complied with.
to inhibitors of metabolism: novel insights into 
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(1992). Killing of virulent Mycobacterium tubercu-
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E. D. (2002). Analysis of nitric oxide synthase and 
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culosis. Am. J. Respir. Crit. Care Med. 166, 178–186.
Cirillo, S. L., Subbian, S., Chen, B., Weisbrod, T. R., 
Jacobs, W. R. Jr., and Cirillo, J. D. (2009). Protection of 
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A., Jacobs, W. R. Jr., Salgame, P., and Alland, D. (2009). 
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and Orme, I. M. (2000). Transient loss of resistance to 
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Ehrt, S., Schnappinger, D., Bekiranov, S., Drenkow, J., 
Shi, S., Gingeras, T. R., Gaasterland, T., Schoolnik, 
G., and Nathan, C. (2001). Reprogramming of the 
macrophage transcriptome in response to interferon-
gamma and Mycobacterium tuberculosis: signaling 
house-keeping and energy metabolism were 
repressed by both stresses. Genes involved in 
iron acquisition were also affected. These data 
are coherent with the hypothesis that insults 
from reactive oxygen and nitrogen interme-
diates are unfavorable to active metabolism 
and growth of Mtb, and the bacteria alters 
expression of related genes to adapt accord-
ingly. A large number of house-keeping and 
energy metabolism related genes were also 
reported to be affected in a similar way by 
Boshoff et al. (2004) who used a wide range 
of drugs, toxic compounds, and stresses 
known to affect metabolism and viability 
of Mtb to study changes to transcriptional 
profile of the bacteria.
Studies such as the one highlighted in 
this commentary that profile global expres-
sion generate a tremendous amount of 
data representing comprehensive response 
to condition being tested. Numerous genes 
identified by Voskuil and colleagues to be 
involved in oxidative and nitrosative stress 
response are annotated as having unknown 
functions. As these genes are characterized 
and functions encoded by them are defined, 
we stand to understand the molecular mech-
anism used by Mtb to adapt to stresses more 
clearly. Databases dedicated to genomics and 
annotation1 and mining of transcriptional 
profiles2 of Mtb can be expected to facilitate 
further understanding of these data.
RefeRences
Boshoff, H. I., Myers, T. G., Copp, B. R., McNeil, M. R., 
Wilson, M. A., and Barry, C. E. III. (2004). The tran-
scriptional responses of Mycobacterium  tuberculosis 
1http://tuberculist.epfl.ch/index.html
2http://www.tbdb.org/
Lamichhane Mycobacterial response to stress
Frontiers in Microbiology | Cellular and Infection Microbiology  August 2011 | Volume 2 | Article 176 | 2


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Mycobacterium Tuberculosis Response to Stress from Reactive Oxygen and Nitrogen Species

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