title: Mycobacterial Cultures Contain Cell Size and Density Specific Sub-populations of Cells with Significant Differential Susceptibility to Antibiotics, Oxidative and Nitrite Stress.
abstract: The present study shows the existence of two specific sub-populations ofMycobacterium smegmatisandMycobacterium tuberculosiscells differing in size and density, in themid-logphase (MLP) cultures, with significant differential susceptibility to antibiotic, oxidative, and nitrite stress. One of these sub-populations (~10% of the total population), containedshort-sizedcells (SCs) generated through highly-deviated asymmetric cell division (ACD) of normal/long-sized mother cells and symmetric cell divisions (SCD) of short-sized mother cells. The other sub-population (~90% of the total population) containednormal/long-sizedcells (NCs). The SCs were acid-fast stainable and heat-susceptible, and contained high density of membrane vesicles (MVs, known to be lipid-rich) on their surface, while the NCs possessed negligible density of MVs on the surface, as revealed by scanning and transmission electron microscopy. Percoll density gradient fractionation of MLP cultures showed theSCs-enrichedfraction (SCF) at lower density (probably indicating lipid-richness) and theNCs-enrichedfraction (NCF) at higher density of percoll fractions. While live cell imaging showed that the SCs and the NCs could grow and divide to form colony on agarose pads, the SCF, and NCF cells could independently regenerate MLP populations in liquid and solid media, indicating their full genomic content and population regeneration potential. CFU based assays showed the SCF cells to be significantly more susceptible than NCF cells to a range of concentrations of rifampicin and isoniazid (antibiotic stress), H2O2(oxidative stress),and acidified NaNO2(nitrite stress). Live cell imaging showed significantly higher susceptibility of the SCs of SC-NC sister daughter cell pairs, formed from highly-deviated ACD of normal/long-sized mother cells, to rifampicin and H2O2, as compared to the sister daughter NCs, irrespective of their comparable growth rates. The SC-SC sister daughter cell pairs, formed from the SCDs of short-sized mother cells and having comparable growth rates, always showed comparable stress-susceptibility. These observations and the presence ofM. tuberculosisSCs and NCs in pulmonary tuberculosis patients' sputum earlier reported by us imply a physiological role for the SCs and the NCs under the stress conditions. The plausible reasons for the higher stress susceptibility of SCs and lower stress susceptibility of NCs are discussed.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Vijay
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Rashmi Ravindran
authors.initials: RR
authors.lastname: Nair
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Deepti
authors.initials: D
authors.lastname: Sharan
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Kishor
authors.initials: K
authors.lastname: Jakkala
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Nagaraja
authors.initials: N
authors.lastname: Mukkayyan
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Sharmada
authors.initials: S
authors.lastname: Swaminath
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Atul
authors.initials: A
authors.lastname: Pradhan
authors.affiliation: Centre for Ecological Sciences, Indian Institute of Science Bangalore, India.
authors.forename: Niranjan V
authors.initials: NV
authors.lastname: Joshi
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science Bangalore, India.
authors.forename: Parthasarathi
authors.initials: P
authors.lastname: Ajitkumar
keywords: antibiotics; asymmetric cell division; heterogeneity; mycobacteria; nitrite stress; oxidative stress; short cells; size and density