Dataset Information

Diverse Bacteria Utilize Alginate Within the Microbiome of the Giant Kelp Macrocystis pyrifera.

ABSTRACT: Bacteria are integral to marine carbon cycling. They transfer organic carbon to higher trophic levels and remineralise it into inorganic forms. Kelp forests are among the most productive ecosystems within the global oceans, yet the diversity and metabolic capacity of bacteria that transform kelp carbon is poorly understood. Here, we use 16S amplicon and metagenomic shotgun sequencing to survey bacterial communities associated with the surfaces of the giant kelp Macrocystis pyrifera and assess the capacity of these bacteria for carbohydrate metabolism. We find that Macrocystis-associated communities are distinct from the water column, and that they become more diverse and shift in composition with blade depth, which is a proxy for tissue age. These patterns are also observed in metagenomic functional profiles, though the broader functional groups-carbohydrate active enzyme families-are largely consistent across samples and depths. Additionally, we assayed more than 250 isolates cultured from Macrocystis blades and the surrounding water column for the ability to utilize alginate, the primary polysaccharide in Macrocystis tissue. The majority of cultured bacteria (66%) demonstrated this capacity; we find that alginate utilization is patchily distributed across diverse genera in the Bacteroidetes and Proteobacteria, yet can also vary between isolates with identical 16S rRNA sequences. The genes encoding enzymes involved in alginate metabolism were detected in metagenomic data across taxonomically diverse bacterial communities, further indicating this capacity is likely widespread amongst bacteria in kelp forests. Overall, the M. pyrifera epibiota shifts across a depth gradient, demonstrating a connection between bacterial assemblage and host tissue state.

SUBMITTER: Lin JD

PROVIDER: S-EPMC6110156 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Diverse Bacteria Utilize Alginate Within the Microbiome of the Giant Kelp <i>Macrocystis pyrifera</i>.

Lin Jordan D JD Lemay Matthew A MA Parfrey Laura W LW

Frontiers in microbiology 20180820

Bacteria are integral to marine carbon cycling. They transfer organic carbon to higher trophic levels and remineralise it into inorganic forms. Kelp forests are among the most productive ecosystems within the global oceans, yet the diversity and metabolic capacity of bacteria that transform kelp carbon is poorly understood. Here, we use 16S amplicon and metagenomic shotgun sequencing to survey bacterial communities associated with the surfaces of the giant kelp <i>Macrocystis pyrifera</i> and as ...[more]

PMID: 30177919

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Project description:Background and aimsThe increased likelihood and severity of storm events has brought into focus the role of coastal ecosystems in provision of shoreline protection by attenuating wave energy. Canopy-forming kelps, including giant kelp (Macrocystis pyrifera), are thought to provide this ecosystem service, but supporting data are extremely limited. Previous in situ examinations relied mostly on comparisons between nominally similar sites with and without kelp. Given that other factors (especially seafloor bathymetry and topographic features) often differ across sites, efforts to isolate the effects of kelp on wave energy propagation confront challenges. In particular, it can be difficult to distinguish wave energy dissipation attributable to kelp from frictional processes at the seabed that often covary with the presence of kelp. Here, we use an ecological transition from no kelp to a full forest, at a single site with static bathymetry, to resolve unambiguously the capacity of giant kelp to damp waves.MethodsWe measured waves within and outside rocky reef habitat, in both the absence and the presence of giant kelp, at Marguerite Reef, Palos Verdes, CA, USA. Nested within a broader kelp restoration project, this site transitioned from a bare state to one supporting a fully formed forest (density of 8 stipes m-2). We quantified, as a function of incident wave conditions, the decline in wave energy flux attributable to the presence of kelp, as waves propagated from outside and into reef habitat.Key resultsThe kelp forest damped wave energy detectably, but to a modest extent. Interactions with the seabed alone reduced wave energy flux, on average, by 12 ± 1.4 % over 180 m of travel. The kelp forest induced an additional 7 ± 1.2 % decrease. Kelp-associated declines in wave energy flux were slightly greater for waves of longer periods and smaller wave heights.ConclusionsMacrocystis pyrifera forests have a limited, albeit measurable, capacity to enhance shoreline protection from nearshore waves. Expectations that giant kelp forests, whether extant or enhanced through restoration, have substantial impacts on wave-induced coastal erosion might require re-evaluation.

Project description:Marine microbes mediate key ecological processes in kelp forest ecosystems and interact with macroalgae. Pelagic and biofilm-associated microbes interact with macroalgal propagules at multiple stages of recruitment, yet these interactions have not been described for Macrocystis pyrifera. Here we investigate the influence of microbes from coastal environments on recruitment of giant kelp, M. pyrifera. Through repeated laboratory experiments, we tested the effects of altered pelagic microbial abundance on the settlement and development of the microscopic propagules of M. pyrifera during recruitment. M. pyrifera zoospores were reared in laboratory microcosms exposed to environmental microbial communities from seawater during the complete haploid stages of the kelp recruitment cycle, including zoospore release, followed by zoospore settlement, to gametophyte germination and development. We altered the microbial abundance states differentially in three independent experiments with repeated trials, where microbes were (a) present or absent in seawater, (b) altered in community composition, and (c) altered in abundance. Within the third experiment, we also tested the effect of nearshore versus offshore microbial communities on the macroalgal propagules. Distinct pelagic microbial communities were collected from two southern California temperate environments reflecting contrasting intensity of human influence, the nearshore Point Loma kelp forest and the offshore Santa Catalina Island kelp forest. The Point Loma kelp forest is a high impacted coastal region adjacent to the populous San Diego Bay; whereas the kelp forest at Catalina Island is a low impacted region of the Channel Islands, 40 km offshore the southern California coast, and is adjacent to a marine protected area. Kelp gametophytes reared with nearshore Point Loma microbes showed lower survival, growth, and deteriorated morphology compared to gametophytes with the offshore Catalina Island microbial community, and these effects were magnified under high microbial abundances. Reducing abundance of Point Loma microbes restored M. pyrifera propagule success. Yet an intermediate microbial abundance was optimal for kelp propagules reared with Catalina Island microbes, suggesting that microbes also have a beneficial influence on kelp. Our study shows that pelagic microbes from nearshore and offshore environments are differentially influencing kelp propagule success, which has significant implications for kelp recruitment and kelp forest ecosystem health.

Dataset Information

Diverse Bacteria Utilize Alginate Within the Microbiome of the Giant Kelp Macrocystis pyrifera.

Publications

Diverse Bacteria Utilize Alginate Within the Microbiome of the Giant Kelp <i>Macrocystis pyrifera</i>.

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