Smoking alters lung microbiome, leading to loss of diversity and community structure

In a recent study published in the journal Access Microbiology, researchers explore the composition of the microbiome and interactions in the lower respiratory tract (LRT) in smokers. 

Study: Lower respiratory tract microbiome composition and community interactions in smokers. Image Credit: vchal / Shutterstock.com

The impact of smoking on the respiratory microbiome

Smoking has been shown to impact resident microbial communities present in different bodily regions. Previous studies have proposed various mechanisms responsible for this association, such as immunosuppression related to smoking, an increase in biofilm formation for specific species, and selection of species by the influence of local oxygen tension.

The upper airways and oral cavities may also directly interact with smoking chemicals, microbes, and heat from cigarettes, which can alter microbiome content. Recent studies have hypothesized that dysbiosis noted in the oral microbiome related to smoking may lead to a greater likelihood of experiencing complications in the respiratory tract among smokers. 

About the study

In the present study, researchers compare the LRT microbiome profiles of active smokers (AS), former smokers (FS), and non-smokers (NS) to describe the bacterial communities present in the lung.

The study involved volunteer subjects aged over 40 years of age who were either smokers of a minimum of 10 pack-years throughout their life or non-smokers. Former smokers qualified for the study if they had abstained from using tobacco for a minimum of 12 months, while AS smoked a minimum of one cigarette within three days of recruitment.

All study participants were required to complete a pulmonary function examination and thorough demographic and clinical questionnaire. The sampling process was standardized for all participants. The team extracted total deoxyribonucleic acid (DNA) from the bronchoalveolar lavages (BALs) specimens.

A single polymerase chain reaction (PCR) assessment was conducted to amplify the V6-V8 region present on the 16S ribosomal ribonucleic acid (rRNA) gene from the metagenomic DNA extracts of the BAL samples. Alpha diversity was estimated using Chao richness and inverse Simpson diversity indices. The DESeq2 algorithm was also used to detect differentiating taxa for each cohort.

Study findings

All 46 smokers reported similar smoking exposure in terms of pack-years, including the FS quitting smoking on an average of about 10 years prior to enrollment. AS and FS exhibited reduced forced vital capacity (FVC), diffusing capacity for carbon monoxide (DL-CO), and forced expiratory volume at second 1 (FEV₁); however, these variations were not remarkable according to the analysis of variance (ANOVA).

Over 3,600 reads with an average length of about 479 nucleotides were documented in each participant’s BAL, which facilitated the description of almost 400 operational taxonomic units (OTUs) per participant. The NS profile was sufficiently balanced between the prevalent phyla Bacteroides, Firmicutes, Proteobacteria, and Actinobacteria with comparatively slightly higher proportions. The FS cohort had a significant increase in Proteobacteria with reduced Bacteroides and Firmicutes levels. This pattern was also true for AS, with Proteobacteria increasing to 75% and Firmicutes declining to 11%.

Genus-level assessments indicated that most of the enhancement in Proteobacteria in AS and FS in comparison to its high proportion in NS was due to the genus Ralstonia, which increased from 2% in the NS, 28% in AS, and 21% in FS.

From the Firmicutes phylum, the Streptococcus and Veillonella genera, as well as Prevotella from the Bacteroidetes phyla exhibited the greatest decline in comparative abundance. Furthermore, the Propionibacterium genus of the Actinobacteria phylum exhibited a slight improvement from 3% in AS and FS to 0.8% in NS.

With respect to the NS profile, a greater number of upper-quartile taxa were distinguished from AS, whereas lower-quartile taxa were distinguished from FS.

NS exhibited a considerably higher mean diversity as compared to AS and FS. The mean diversity further increased when the participants were placed by declining richness, thus indicating that NS reported higher richness. Yet, the diversity evaluated with the inverse Simpson index had only an intermediate association with richness estimates and the participant’s smoking status.

Conclusions

The current study provides new insights into the complicated microbial communities found in the LRT and how this microbiome can be changed under different smoking conditions. The researchers also observed that the oral microbiota can settle in the lungs of smokers, which makes the study of the upper airway microbiome interesting for future research.

The microbiomes of former smokers appear to exhibit similar properties to those of both AS and NS. In the future, integration of the present findings with next-generation analytical techniques would help establish the effect of such microbial communities on human health.