Effect of sonic stimulation on Bacillus endospore germination

Area of Science:

• Microbiology
• Acoustics
• Biophysics

Background:

• Bacillus endospores are dormant structures requiring specific conditions for germination.
• Understanding endospore germination mechanisms is crucial for sterilization and disinfection applications.
• External physical factors influencing germination are not fully understood.

Purpose of the Study:

• To investigate the effect of sonic stimulation on Bacillus endospore germination.
• To elucidate the role of acoustic energy in modulating germination kinetics.
• To explore potential differences in response between Bacillus species.

Main Methods:

• Germinating endospores were exposed to audible sound waves (5 kHz, 90 dB) using piezoelectric transducers.
• Germination kinetics were monitored in situ using terbium-dipicolinate fluorescence assay, optical density, and phase contrast microscopy.
• Spore aspect ratios of Bacillus atrophaeus and Bacillus subtilis were measured.

Main Results:

• Sonic stimulation (5 kHz, 90 dB) increased Bacillus atrophaeus germination speed by 43.7% ± 11.3% and final germination by 61.7% ± 11.9%.
• No significant acoustic effect was observed on Bacillus subtilis endospore germination.
• Differences in spore aspect ratio (B. atrophaeus: 1.43 ± 0.05; B. subtilis: 2.02 ± 0.08) may explain the differential response.

Conclusions:

• Audible sound waves can promote Bacillus endospore germination, likely by altering membrane permeability and enzyme activity.
• The differential response suggests that spore morphology influences acoustic energy absorption and subsequent germination.
• This study highlights the potential of external fields for controlling endospore germination and understanding cell-wave interactions.