Bdellovibrio bacteriovorus 109J is a predatory bacterium which lives by predating on other Gram-negative bacteria to obtain the nutrients it needs for replication and survival. Here, we evaluated the effects two classes of bacterial signaling molecules (acyl homoserine lactones (AHLs) and diffusible signaling factor (DSF)) have on B. bacteriovorus 109J behavior and viability. While AHLs had a non-significant impact on predation rates, DSF considerably delayed predation and bdelloplast lysis. Subsequent experiments showed that 50 μM DSF also reduced the motility of attack-phase B. bacteriovorus 109J cells by 50% (38.2 ± 14.9 vs. 17 ± 8.9 μm/s). Transcriptomic analyses found that DSF caused genome-wide changes in B. bacteriovorus 109J gene expression patterns during both the attack and intraperiplasmic phases, including the significant downregulation of the flagellum assembly genes and numerous serine protease genes. While the former accounts for the reduced speeds observed, the latter was confirmed experimentally with 50 μM DSF completely blocking protease secretion from attack-phase cells. Additional experiments found that 30% of the total cellular ATP was released into the supernatant when B. bacteriovorus 109J was exposed to 200 μM DSF, implying that this QS molecule negatively impacts membrane integrity.
Bdellovibrio
and like organisms are predatory bacteria that are capable of attacking, killing, and consuming many bacterial pathogens, including multidrug-resistant strains. These qualities have led to them being labeled as “living antibiotics.” Research work with these remarkable strains, however, has been hampered by long growth times needed to quantify the predatory populations through plaque assays, which typically take 4 days to develop.
In a survey of the International Space Station (ISS), the most common pathogenic bacterium identified in samples from the air, water and surfaces was Staphylococcus aureus. While growth under microgravity is known to cause physiological changes in microbial pathogens, including shifts in antibacterial sensitivity, its impact on S. aureus is not well understood. Using high-aspect ratio vessels (HARVs) to generate simulated microgravity (SMG) conditions in the lab, we found S. aureus lipid profiles are altered significantly, with a higher presence of branch-chained fatty acids (BCFAs) (14.8% to 35.4%) with a concomitant reduction (41.3% to 31.4%) in straight-chain fatty acids (SCFAs) under SMG. This shift significantly increased the sensitivity of this pathogen to daptomycin, a membrane-acting antibiotic, leading to 12.1-fold better killing under SMG. Comparative assays with two additional compounds, i.e., SDS and violacein, confirmed S. aureus is more susceptible to membrane-disrupting agents, with 0.04% SDS and 0.6 mg/L violacein resulting in 22.9- and 12.8-fold better killing in SMG than normal gravity, respectively. As humankind seeks to establish permanent colonies in space, these results demonstrate the increased potency of membrane-active antibacterials to control the presence and spread of S. aureus, and potentially other pathogens.
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