Vibrio harveyi Exhibits the Growth Advantage in Stationary Phase Phenotype during Long-Term Incubation

The bioluminescent marine bacterium Vibrio harveyi can exist within a host, acting as a mutualist or a parasitic microbe, and as planktonic cells in open seawater. This study demonstrates the ability of V. harveyi populations to survive and adapt under nutrient stress conditions in the laboratory, starting in an initially rich medium. V. harveyi populations remain viable into long-term stationary phase, for at least 1 month, without the addition of nutrients. To determine whether these communities are dynamic, populations were sampled after 10, 20, and 30 days of incubation and examined for their competitive ability when cocultured with an unaged, parental population. While populations incubated for 10 or 20 days showed some fitness advantage over parental populations, only after 30 days of incubation did all populations examined outcompete parental populations in coculture, fully expressing the growth advantage in stationary phase (GASP) phenotype. The ability to express GASP, in the absence of additional nutrients after inoculation, verifies the dynamism of long-term stationary-phase V. harveyi populations, implies the ability to generate genetic diversity, and demonstrates the plasticity of the V. harveyi genome, allowing for rapid adaptation for survival in changing culture environments. Despite the dynamism, the adaptation to the changing culture environment occurs less rapidly than in Escherichia coli, possibly due to Vibrio harveyi's lower mutation frequency. IMPORTANCE Vibrio harveyi populations exist in many different niches within the ocean environment, as free-living cells, symbionts with particular squid and fish species, and parasites to other marine organisms. It is important to understand V. harveyi's ability to survive and evolve within each of these niches. This study focuses on V. harveyi's lifestyle outside the host environment, demonstrating this microbe's ability to survive long-term culturing after inoculation in an initially rich medium and revealing increased competitive fitness correlated with incubation time when aged V. harveyi populations are cocultured with unaged, parental cultures. Thus, this study highlights the development of the growth advantage in stationary phase (GASP) phenotype in V. harveyi populations suggesting a dynamic population with fluctuating genotype frequencies throughout long-term, host-independent incubation.

Amplicon sequencing reveals significantly increased Vibrio abundance and associated gene functions in vibriosis-infected black tiger shrimp (Penaeus monodon)

Vibriosis caused by luminous Vibrio species is one of the biggest challenges to shrimp industry in Bangladesh. This study aimed to characterize whole microbial communities from Vibrio-infected black tiger shrimp (Penaeus monodon) using 16S rRNA-based amplicon sequencing. A total of 36 disease-free and infected shrimp were collected from six different hatcheries in Bagerhat, Bangladesh. A final pool of 12 samples (n = 6) was created by homogenization of the hepatopancreas samples from three shrimps collected from each hatchery for the same group. The amplicon sequencing data revealed significant (p < .05) decrease of alpha diversity measurements and subsequent effects (p < .05) on the hepatopancreas microbiota in the infected group, compared to control shrimp. Proteobateria and Aeromonas were the most dominant bacteria at phylum and genus level in both groups and identified as core microbiota in the community. Two bacterial groups at phyla level and eight at genus level were found associated with the alteration of hepatopancreas microbial communities and associated gene functions in vibriosis-infected shrimp, revealed by differential abundance and KEGG pathway analysis. The overwhelming abundance of Citroibacter, Shewanella and Candidatus lineages in vibriosis-infected shrimp needs further investigations.