Hemolymph of healthy Doclea rissoni Leach, 1815: A pool for Vibrionaceae?

As diseases have a great impact on the population dynamics, evolution and immune biology of affected organisms, it is important to understand the modes and mechanisms of interaction among the lower animals and their microbial symbionts in nature function together for survival. To achieve this, it is important to understand the community structure of the native flora of these animals. Spider crabs are well known for their tolerance to various pollutants. Nevertheless, the microbiology of their circulatory systems and their role in disease transmission are unknown. Therefore, the bacteria associated with the hemolymph of a spider crab, Doclea rissoni in its natural ecosystem was characterized. Nine healthy crabs were collected from the coastal areas of Kochi, and their hemolymphs were collected. Enumeration of viable bacteria using various media revealed a similar count in all the media (7-10×102 CFU/ml). Characterization of representative isolates by conventional microbiological methods and 16S rRNA gene sequencing was followed. Despite using three different media, all isolates belonged to a single family Vibrionaceae. There were two genera as Vibrio (86.67%) and Photobacterium (13.33%). Among Vibrio, five species belonging to three different clades were isolated, of which two could not be assigned to any known species. These were classified as novel species (belonging to Harveyi clade and, Brasiliensis clade) and their description is underway. The order of relative abundance was V. alginolyticus>Novel Vibrio-II>P. damselae>V. furnissii / V. parahaemolyticus / Novel Vibrio-I. Of these, V. alginolyticus, P. damselae and V. furnissii are implicated in occasional disease outbreaks in humans and animals, posing an increased risk to human economic activity, notably aquaculture practices. Therefore, further investigations are required to find the basis for the mutualistic relationship of vibrios in different crabs