Diversity and specificity of microplastic-associated bacterial communities: evidences from a marine coral microcosm system

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FrancoAngel_2020_06_18.pdf (7.69 MB)

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2020

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DOI:
http://dx.doi.org/10.22029/jlupub-16784

Abstract

Corals are complex organisms in a delicate balance with symbiotic algae, fungi, bacteria, archaea, and viruses, which constitute the coral holobiont. Coverage and survival of coral reefs decrease rapidly due to changes in environmental conditions induced by human activities including, among others, the plastic pollution. Few studies have focused on the effects of plastic pollution on coral health, even though the research on microplastics (MP) in the ocean is imperative since MP are ubiquitous in aquatic systems, subjected to bacterial colonisation, dispersion among ecosystems, and ingestion by animals being transferred within the food web.The hypothesis on which the study is based suggests that MP harbour specific bacterial assemblages that differ from those on other particles and that MP act as vectors of non-native and potential pathogenic bacteria that may be involved in the health impairment of corals, which was observed in corals exposed to MP in the CEMarin aquatic system. Bacterial assemblages associated with different habitats within the system: MP, sandy sediments, detritus, and present in the > 5µm, the 0.22-5µm, and the total water fractions, were investigated by cultivation-dependent and independent approaches. A closer examination of isolates of genera Roseivivax, Marinobacter, Roseivivax, and especially Vibrio was performed due to their relevance as potential coral pathogens.Differences in structure and composition of the bacterial assemblages associated with the particles and water fractions were observed, as well as MP-specific bacterial assemblages with high abundances of Jejudonia, Roseivivax, Marinobacter, and Erythrobacter, not present in any other sample. Quantitative PCR revealed a higher abundance of Vibrio spp. 16S rRNA gene copies per ng total DNA from MP compared to sandy sediments. The most abundant genera identified in the 16S rRNA gene amplicon sequencing were also isolated from the different samples. This approach indicated that Vibrio was the most abundant genus of the cultured community, and through a deep analysis based on 16S rRNA gene phylotyping, multilocus sequence analysis (MLSA), and genotyping, a higher genetic diversity of Vibrio spp. was observed. The strains were more closely related to Vibrio alginolyticus, Vibrio fortis, Vibrio coralliilyticus, Vibrio mediterranei, and Vibrio owensii, most of them coral pathogens. The genome of selected MP-associated bacteria was sequenced and by using comparative genomics, genes involved in the degradation of complex polymers, as well as genes associated to pathogenicity were detected, which may be related to coral diseases and the health impairment observed in corals incubated in the CEMarin aquarium system. In addition, four isolates from the strain collection represented new species, described as Winogradskyella pocilloporae, Pseudomaribius plastisphaeri, Ruegeria sedimentorum, and Vibrio aquimaris.These findings validate the proposed hypothesis and represent a starting point to unravel the potential effects of MP-associated bacterial communities on coral s health. The strain collection may serve as base for future studies aimed to strengthen the knowledge of plastic biodegradation and bacterial pathogenicity on corals to identify the causes, mitigate their effects, and contribute to the conservation of these ecosystems.

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Anthology

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