Effects of nutritional and ambient oxygen condition on biofilm formation in Mycobacterium avium subsp. hominissuis via altered glycolipid expression

Takahiro Totani,Mamiko Niki,Yutaka Yoshida,Yukihiro Kaneko,Yoshitaka Tateishi,Yukiko Nishiuchi,Hiromi Kitanaka,Sohkichi Matsumoto

doi:10.1038/srep41775

Abstract

Mycobacterium avium subsp. hominissuis (MAH) is the major causative agent of nontuberculous mycobacteriosis, the representative case of environment-related infectious diseases the incidence of which is increasing in industrialized countries. MAH is found in biofilm in drinking water distribution system and residential environments. We investigated the effect of gaseous and nutritional conditions, and the role of glycopeptidolipids (GPLs) on biofilm-like pellicle formation in MAH. Pellicle formation was observed under 5% oxygen in Middlebrook 7H9 broth containing 0.2% glycerol and 10% albumin-dextrose-catalase enrichment but not under normoxia or in nutrient-poor media. An analysis of 17 environmental isolates revealed that hypoxia (5% oxygen) preferentially enhanced pellicle formation both in plastic plates and in glass tubes, compared with hypercapnia (5% carbon dioxide). Wild-type strains (WT) developed much thicker pellicles than GPL-deficient rough mutants (RM). WT bacterial cells distributed randomly and individually in contrast to that RM cells positioned linearly in a definite order. Exogenous supplementation of GPLs thickened the pellicles of RM, resulting in a similar morphological pattern to WT. These data suggest a significant implication of eutrophication and hypoxia in biofilm-like pellicle formation, and a functional role of GPLs on development of pellicles in MAH.

Highlights

As well as M. tuberculosis are known to form pellicles in experimental culture conditions, a sort of the biofilm structure consisting of clustered bacterial cells with self-produced matrix[12,13,14,15,16,17]
We demonstrated special characteristics of biofilm-like pellicle formation by Mycobacterium avium subsp. hominissuis (MAH), which has emerged as an important cause of infectious diseases in industrialised countries in the last decade[1,2], as follows: (1) Eutrophication and hypoxia are necessary factors for pellicle formation
These conditions and contributing molecules for biofilm-like pellicle formation seem to be quite distinct in MAH compared with those in other bacterial species such as Vibrio, Staphylococci and Pseudomonas[35,36,37], because oligotrophy and exopolysaccharides play important role in biofilm formation in such general bacteria

Summary

Introduction

As well as M. tuberculosis are known to form pellicles in experimental culture conditions, a sort of the biofilm structure consisting of clustered bacterial cells with self-produced matrix[12,13,14,15,16,17]. In M. avium, mutants of genes encoding GPL synthesis enzymes, as well as those encoding tricarboxylic acid cycle and other hypothetical membrane proteins impair pellicle formation, invasiveness in human bronchial epithelial cells, and virulence in mice when infected by aerosol[27,28]. These findings suggest that GPLs may have a critical role in MAH during biofilm growth, compared with planktonic growth. We determined the role of cell wall components, e.g. mycobacterial cell wall lipids, including GPLs and other glycolipids, on pellicle formation by MAH

Methods

Results

Conclusion