Viability Analysis and Cell Morphology Observation of Vibrio alginolyticus under Long-term Starvation

Key words: 
• Vibrio alginolyticus /
• starvation /
• phase variation /
• colonial morphology /
• virulence

Abstract: Three Vibro alginolyticus strains（ ZJ-51,E324 and E381） with phase variation were selected to conduct seawater long-term starvation experiments to study viable bacteria density at different periods,colony morphology observation under optical microscope,cell morphology observation under scanning electron microscope（ SEM） and the virulence to Artemia salina between the fresh and the starved. There are three phases according to bacteria activity undergoing long-term starvation. The cultured bacteria activities increased and peaked during the early period（ 1~5 d）,and the colonial morphologies did not show significant changes. During the middle phase of starvation（ 5~40 d）,cultured bacterial cells decreased dramatically,and part of colonial movement rings shrunk. After about 41 d starvation,the populations entered into a long-term stationary phase and the cultured bacteria density maintained at 10³~10⁴ cfu·m L^-1. Viable bacteria,with tiny colonies formed on the LA agar plates,remained at about 10³cfu·m L^-1after 500 d starvation. Under SEM a large portion of cells changed from short rod shape to coccus shape,and a small portion of cells displayed long rod shape or produced flocs.The results of virulence to A. salina show that after being starved for 500 d,the cells of V. alginolyticus decreased half of their lethality as compared to the normal cells. These results provide important clues for the survival strategy of V. alginolyticus in the oligotrophic seawater environment.