Spaceflight promotes biofilm formation by Pseudomonas aeruginosa

Abstract

Understanding the effects of spaceflight on microbial communities is crucial for the success of long-term, manned space missions. Surface-associated bacterial communities, known as biofilms, were abundant on the Mir space station and continue to be a challenge on the International Space Station. The health and safety hazards linked to the development of biofilms are of particular concern due to the suppression of immune function observed during spaceflight. While planktonic cultures of microbes have indicated that spaceflight can lead to increases in growth and virulence, the effects of spaceflight on biofilm development and physiology remain unclear. To address this issue, Pseudomonas aeruginosa was cultured during two Space Shuttle Atlantis missions: STS-132 and STS-135, and the biofilms formed during spaceflight were characterized. Spaceflight was observed to increase the number of viable cells, biofilm biomass, and thickness relative to normal gravity controls. Moreover, the biofilms formed during spaceflight exhibited a column-and-canopy structure that has not been observed on Earth. The increase in the amount of biofilms and the formation of the novel architecture during spaceflight were observed to be independent of carbon source and phosphate concentrations in the media. However, flagella-driven motility was shown to be essential for the formation of this biofilm architecture during spaceflight. These findings represent the first evidence that spaceflight affects community-level behaviors of bacteria and highlight the importance of understanding how both harmful and beneficial human-microbe interactions may be altered during spaceflight.

Figure 1. Spaceflight increases biofilm formation by P. aeruginosa.

Wild-type P. aeruginosa was cultured under normal gravity (black bars) and spaceflight (grey bars) conditions in mAUM or mAUMg containing 5 or 50 mM phosphate. (A) The number of surface-associated viable cells per cellulose ester membrane. (B) Biofilm biomass and (C) mean biofilm thickness were quantified by analysis of CLSM images. Error bars, SD; N = 3. *p≤0.05, **p≤0.01.

Figure 2. P.aeruginosa biofilms cultured during spaceflight display column-and-canopy structures.

Confocal laser scanning micrographs of 3-day-old biofilms formed by wild type, ΔmotABCD, and ΔpilB comparing normal gravity and spaceflight culture conditions. All strains were grown in mAUMg with 5 mM phosphate. No significant differences in structure or thickness were observed with mAUMg containing 5 or 50 mM phosphate. (A) Representative side-view images. (B) Representative 5.8 µm thick slices generated from partial z stacks. Maximum thickness is indicated in the upper right corner of the top slice for each condition.

Figure 3. Increased oxygen availability minimizes gravitational effects on biofilm formation by P.aeruginosa.

Representative side view confocal laser scanning micrographs of 3-day-old biofilms formed by wild-type P. aeruginosa and ΔmotABCD grown in mAUMg with gas exchange (GE) inserts comparing normal gravity and spaceflight culture conditions.

Figure 4. Illustration summarizing the influence of gravity, flow, and motility on P.aeruginosa biofilm architecture.