Abstract
Pinna nobilis populations, constituting the largest bivalve mollusk endemic to the Mediterranean, is characterized as critically endangered, threatened by extinction. Among the various factors proposed as etiological agents are the Haplosporidium pinnae and Mycobacterium sp. parasites. Nevertheless, devastation of the fan mussel populations is still far from clear. The current work is undertaken under a broader study aiming to evaluate the health status of Pinna nobilis population in Aegean Sea, after the mass mortalities that occurred in 2019. A significant objective was also (a) the investigation of the etiological agents of small-scale winter mortalities in the remaining populations after the devastating results of Haplosporidium pinnae and Mycobacterium sp. infections, as well as (b) the examination of the susceptibility of the identified bacterial strains in antibiotics for future laboratory experiments. Microbiological assays were used in order to detect the presence of potential bacterial pathogens in moribund animals in combination with molecular tools for their identification. Our results provide evidence that Vibrio bacterial species are directly implicated in the winter mortalities, particularly in cases where the haplosporidian parasite was absent. Additionally, this is the first report of Vibrio mediterranei and V. splendidus hosted by any bivalve on the Greek coastline.
Highlights
Marine habitats constitute natural hosts for a plethora of microorganism communities, which play key roles in fundamental functions among each ecosystem [1]
All examined samples were found positive to Mycobacterium sp., whereas only 3 out of the 17 were positive to H. pinnae infection (Table 1)
In regard to bacteria cultures, alignment was based on a 950 bp long partial sequence of the 16r RNA gene that defined ten different haplotypes, all belonging to various species of the genus Vibrio (Table 1, Figure 3)
Summary
Marine habitats constitute natural hosts for a plethora of microorganism communities, which play key roles in fundamental functions among each ecosystem [1]. Microbes are often engaged in a mutualistic symbiosis with many inhabitants in marine environments, assisting them in mechanisms such as immune functions, physiological responses in various factors, and nutrient uptake [2,3,4]. Apart from the beneficial properties sometimes offered to the hosts, microbes can act pathogenically under certain conditions and may become opportunistic, leading to disease pathogenesis [5]. Stressful conditions as a result of climate change can have a negative impact on the physiological responses of hosts, as well as implicating with lower immune responses [6,7]. Parasitism can expose the host species to secondary infections, which, together with the main causative agent, can increase the pathogenicity at the expense of the host [9,10]
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