Genomes and Virulence Factors of Novel Bacterial Pathogens Causing Bleaching Disease in the Marine Red Alga Delisea pulchra

Abstract

Nautella sp. R11, a member of the marine Roseobacter clade, causes a bleaching disease in the temperate-marine red macroalga, Delisea pulchra. To begin to elucidate the molecular mechanisms underpinning the ability of Nautella sp. R11 to colonize, invade and induce bleaching of D. pulchra, we sequenced and analyzed its genome. The genome encodes several factors such as adhesion mechanisms, systems for the transport of algal metabolites, enzymes that confer resistance to oxidative stress, cytolysins, and global regulatory mechanisms that may allow for the switch of Nautella sp. R11 to a pathogenic lifestyle. Many virulence effectors common in phytopathogenic bacteria are also found in the R11 genome, such as the plant hormone indole acetic acid, cellulose fibrils, succinoglycan and nodulation protein L. Comparative genomics with non-pathogenic Roseobacter strains and a newly identified pathogen, Phaeobacter sp. LSS9, revealed a patchy distribution of putative virulence factors in all genomes, but also led to the identification of a quorum sensing (QS) dependent transcriptional regulator that was unique to pathogenic Roseobacter strains. This observation supports the model that a combination of virulence factors and QS-dependent regulatory mechanisms enables indigenous members of the host alga's epiphytic microbial community to switch to a pathogenic lifestyle, especially under environmental conditions when innate host defence mechanisms are compromised.

Habitat-specific environmental conditions primarily control the microbiomes of the coral Seriatopora hystrix

“…Principal component analysis identified 17 OTUs, in addition to the Endozoicomonas OTUs (OTU 69 and 71), which were responsible for driving the differences in microbial communities associated with the different samples. These other OTUs were related to members of the Rhodobacterales and Vibrionales, several members of which have previously been identified as putative pathogens, or associated with disease lesions of scleractinian corals and other marine invertebrates (Imai et al, 2006;Koren and Rosenberg, 2008;Becker et al, 2009;Sekar et al, 2009;Sunagawa et al, 2009;Case et al, 2011;Fernandes et al, 2011;Figure 3b). OTUs from these groups were also found to have a highly significant negative correlation to Endozoicomonas.…”

Laboratory-Cultured Strains of the Sea Anemone Exaiptasia Reveal Distinct Bacterial Communities

“…Further, bacteria of the genus Photobacterium are remarkably resistant to ultraviolet radiation (e.g., UVB; Matallana-Surget et al, 2009) and have been associated with coral bleaching (Thompson et al, 2005;Moreira et al, 2014). Also linked to bleaching is Nautella italica, a bacterial pathogen that can invade, colonize, and induce bleaching in marine macroalgae (Fernandes et al, 2011). Knowledge of the ecology and functional importance of these bacteria is still lacking, and is crucial to better understand their role in shaping the core microbiome of Exaiptasia.…”

Evolutionary Ecology of the Marine Roseobacter Clade

“…In addition to living freely in bulk seawater (10,11), roseobacters are dominant members of the bacterial communities associated with phytoplankton (12)(13)(14)(15)(16)(17), macroalgae (18,19), and various marine animals (20)(21)(22)(23). Both mutualistic (24,25) and pathogenic (26)(27)(28)(29) life-styles have been suggested. Clade members are ubiquitous in temperate and polar oceans (30); the latter include sea ice habitats, in which Roseobacter is a major bacterial phylotype (31,32).…”