Impact of Simulated pH Conditions on Phenotypic Expression in Shrimp Pathogenic and Non-Pathogenic Vibrio campbellii Strains

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Environmental pH fluctuation in oceanic and marine ecosystems can significantly impact the distribution and behavior of pathogenic Vibrio species, including their interactions with marine invertebrates such as crustaceans. This study focused on Vibrio campbellii, a common shrimp pathogen, and its phenotypic responses to varying pH conditions. Both pathogenic strain HY01 and non-pathogenic strain ATCC BAA-1116 were cultured in 30 pL/L Luria-Bertani Sea Salt under 3 pH conditions, including pH 6 (slightly acidic), pH 8 (representing the oceanic pH), and pH 9 (alkaline). Growth patterns and phenotypic traits were evaluated. Results revealed no significant growth difference between the 2 strains under the different pH conditions, although the non-pathogenic strain showed a slight growth reduction at pH 9 during the exponential phase. Both strains were able to buffer environmental pH shifts, adjusting to near-oceanic pH levels (around pH 8). At pH 9, a stressor level for V. campbellii, delays were observed in bioluminescence, biofilm formation, exopolysaccharide production, shrimp surface colonization, motility, and caseinase production, affecting both strains. In contrast, mildly acidic conditions (pH 6) induced the highest expression of several phenotype traits. Statistical analyses indicated significant interactions between strain type and pH levels in influencing phenotypic expression. In conclusion, the pathogenic V. campbellii strain HY01 exhibited greater adaptability and virulence across various pH conditions compared to the non-pathogenic ATCC BAA-1116, emphasizing pH as a critical environmental factor in shaping the growth and pathogenic potential of V. campbellii. Our studies provide valuable insights into managing pH conditions in aquaculture environments to optimize proper shrimp cultivation and prevent cross-contamination of V. campbellii from seawater habitats to farms. These findings provide a physiological profile of Vibrio under pH stress, which can support the development of predictive outbreak models to assess the risk of luminous vibriosis, especially in to seasonal changes and ocean acidification. HIGHLIGHTS The shrimp pathogenic Vibrio campbellii strain HY01 demonstrated stronger survival and higher virulence compared to the non-pathogenic campbellii strain ATCC BAA-1116 under both acidic and basic pH conditions. Both pathogenic and non-pathogenic campbellii strains adjusted the initial pH of their cultures to more optimal levels for growth and phenotypic expression. Slightly acid to slightly alkaline conditions supported favorable environments, enhancing growth, bioluminescence, biofilm formation, exopolysaccharide production, shrimp colonization, swimming motility, and protease production in both campbellii strains. Extreme alkalinity was identified as a pH stressor for campbellii strains, suppressing phenotypic expressions without inhibiting growth. These findings provide detailed phenotypic profiles of pathogenic and non-pathogenic campbellii strains in response to pH fluctuations during their growth stages. GRAPHICAL ABSTRACT

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