Abstract
Microorganisms are increasingly being recognized as the causative agents in the diseases of marine higher organisms, such as corals, sponges, and macroalgae. Delisea pulchra is a common, temperate red macroalga, which suffers from a bleaching disease. Two bacterial strains, Nautella italica R11 and Phaeobacter gallaeciensis LSS9, have been shown in vitro to cause bleaching symptoms, but previous work has failed to detect them during a natural bleaching event. To provide a link between in vitro observations and natural occurrences of the disease, we employ here deep-sequencing of the 16S rRNA gene to comprehensively analyze the community composition of healthy and diseased D. pulchra samples from two separate locations. We observed operational taxonomic units (OTUs) with 100% identity and coverage to the 16S RNA gene sequence of both in vitro pathogens, but only the OTU with similarity to strain LSS9 showed a statistically significant higher abundance in diseased samples. Our analysis also reveals the existence of other bacterial groups within the families Rhodobacteraceae and Flavobacteriaceae that strongly contribute to difference between diseased and healthy samples and thus these groups potentially contain novel macroalgal pathogens and/or saprophytes. Together our results provide evidence for the ecological relevance of one kind of in vitro pathogen, but also highlight the possibility that multiple opportunistic pathogens are involved in the bleaching disease of D. pulchra.
Highlights
Marine sessile macroorganisms, such as seaweed, sponges, and corals, are often colonized by a large number and diversity of bacteria, with which they can have either positive, neutral or negative interactions (Ainsworth et al, 2010; Egan et al, 2012; Hollants et al, 2013)
DEEP 16S rRNA GENE SEQUENCING OF MICROBIAL COMMUNITIES SHOWS operational taxonomic units (OTUs) MATCHING IN VITRO PATHOGENS IN ENVIRONMENTAL SAMPLES In this study we analyzed replicate samples for two separate bleaching events of natural D. pulchra populations in two locations (Bare Island and Long Bay) that occurred during the austral summer of 2008 (Campbell et al, 2011)
Rarefaction analysis indicated that the sequencing effort started to saturate the diversity of the 16S rRNA gene fragment for all samples and this was further supported by Good’s coverage estimates of greater than 97% for both OTU definitions
Summary
Marine sessile macroorganisms, such as seaweed, sponges, and corals, are often colonized by a large number and diversity of bacteria, with which they can have either positive, neutral or negative interactions (Ainsworth et al, 2010; Egan et al, 2012; Hollants et al, 2013). Two pathogens, Nautella italica R11 and Phaeobacter gallaeciensis LSS9, have been isolated that can cause the bleaching disease in vitro (Case et al, 2011; Fernandes et al, 2011) In the laboratory, these two pathogens can invade the tissue of D. pulchra under conditions of elevated temperature and when the alga’s chemical defense based on UV-sensitive molecules called furanones is reduced. The previous inability of Fernandes et al (2012) to detect N. italica R11 and P. gallaeciensis LSS9 in vivo may be due to the limited number of samples analyzed and/ or the relatively shallow sequencing analysis of the microbial community of D. pulchra To address this issue, we use here deep-sequencing of the 16S rRNA gene to investigate the microbial community on healthy and bleached individuals from two, natural disease events
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
