Affiliation:
1. Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
2. Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, India
Abstract
ABSTRACT
Bacteria respond to stressful growth conditions through a conserved phenomenon of stringent response mediated by synthesis of stress alarmones ppGpp and pppGpp [referred to as (p)ppGpp]. (p)ppGpp synthesis is known to occur by ribosome-associated RelA. In addition, a dual-function protein, SpoT (with both synthetase and hydrolase activities), maintains (p)ppGpp homeostasis. The presence of (p)ppGpp is also known to contribute to antibiotic resistance in bacteria.
Mycobacterium smegmatis
possesses Arr, which inactivates rifampin by its ADP ribosylation. Arr has been shown to be upregulated in response to stress. However, the roles Arr might play during growth have remained unclear. We show that Arr confers growth fitness advantage to
M. smegmatis
even in the absence of rifampin. Arr deficiency in
M. smegmatis
resulted in deficiency of biofilm formation. Further, we show that while Arr does not interact with the wild-type
Escherichia coli
ribosomes, it interacts with them when the
E. coli
ribosomal protein L11 (a stringent response regulator) is replaced with its homolog from
M. smegmatis
. The Arr interaction with
E. coli
ribosomes occurs even when the N-terminal 33 amino acids of its L11 protein were replaced with the corresponding sequence of
M. smegmatis
L11 (
Msm-Eco
L11 chimeric protein). Interestingly, Arr interaction with the
E. coli
ribosomes harboring
M. smegmatis
L11 or
Msm-Eco
L11 results in the synthesis of ppGpp
in vivo
. Our study shows a novel role of antibiotic resistance gene
arr
in stress response.
IMPORTANCE
Mycobacterium smegmatis
, like many other bacteria, possesses an ADP-ribosyltransferase, Arr, which confers resistance to the first-line antituberculosis drug, rifampin, by its ADP ribosylation. In this report, we show that in addition to its known property of conferring resistance to rifampin, Arr confers growth fitness advantage to
M. smegmatis
even when there is no rifampin in the growth medium. We then show that Arr establishes species-specific interactions with ribosomes through the N-terminal sequence of ribosomal protein L11 (a stringent response regulator) and results in ppGpp (stress alarmone) synthesis. Deficiency of Arr in
M. smegmatis
results in deficiency of biofilm formation. Arr protein is physiologically important both in conferring antibiotic resistance as well as in mediating stringent response.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
8 articles.
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