Abstract
Mass mortality events due to disease outbreaks have recently affected almost every healthy population of fan mussel, Pinna nobilis in Mediterranean Sea. The devastating mortality of the species has turned the interest of the research towards the causes of these events. After the haplosporidan infestation and the infection by Mycobacterium sp., new emerging pathogens have arisen based on the latest research. In the present study, a metagenomic approach of 16S rRNA next generation sequencing (NGS) was applied in order to assess the bacterial diversity within the digestive gland of diseased individuals as well as to carry out geographical correlations among the biodiversity of microbiome in the endangered species Pinna nobilis. The specimens originated from the mortalities occurred in 2019 in the region of Greece. Together with other bacterial genera, the results confirmed the presence of Vibrio spp., assuming synergistic effects in the mortality events of the species. Alongside with the presence of Vibrio spp., numerous bacterial genera were detected as well, including Aliivibrio spp., Photobacterium spp., Pseudoalteromonas spp., Psychrilyobacter spp. and Mycoplasma spp. Bacteria of the genus Mycoplasma were in high abundance particularly in the sample originated from Limnos island representing the first time recorded in Pinna nobilis. In conclusion, apart from exclusively the Haplosporidan and the Mycobacterium parasites, the presence of potentially pathogenic bacterial taxa detected, such as Vibrio spp., Photobactrium spp. and Alivibrio spp. lead us to assume that mortality events in the endangered Fan mussel, Pinna nobilis, may be attributed to synergistic effects of more pathogens.
Highlights
Microbial communities constitute the subject of numerous studies for many years, which have been mostly relied on culture dependent methods for detection, identification and characterizationPathogens 2020, 9, 1002; doi:10.3390/pathogens9121002 www.mdpi.com/journal/pathogensPathogens 2020, 9, 1002 of virulence traits of various pathogens [1]
The present study demonstrated a great variability of symbiotic bacteria within the infected
P. nobilis specimens originating from mass mortality events in Greece
Summary
Microbial communities constitute the subject of numerous studies for many years, which have been mostly relied on culture dependent methods for detection, identification and characterizationPathogens 2020, 9, 1002; doi:10.3390/pathogens9121002 www.mdpi.com/journal/pathogensPathogens 2020, 9, 1002 of virulence traits of various pathogens [1]. Research on the microbiota of aquatic animals has indicated its important role in many key functions such as immune responses-disease resistance, proper assimilation of nutrients through good intestine function and stimulation of biological processes [5,6]. This relationship is reciprocal for the microbiome and the host, due to the provision of a stable and nutritious environment provided by the host [7,8]. Global warming because of climate change may result to lower immune responses and physiological performance in aquatic organisms [9]. As a result of the decline in immune responses, opportunistic pathogens, that may already belong to microbiome of the host, take advantage of that opportunity and multiply, creating colonies uncontrollably, to the detriment of the host [10,11]
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