Dataset Information

Bacterial Diversity Associated with the Coccolithophorid Algae Emiliania huxleyi and Coccolithus pelagicus f. braarudii.

ABSTRACT: Coccolithophores are unicellular calcifying marine phytoplankton that can form large and conspicuous blooms in the oceans and make significant contributions to oceanic carbon cycling and atmospheric CO2 regulation. Despite their importance, the bacterial diversity associated with these algae has not been explored for ecological or biotechnological reasons. Bacterial membership of Emiliania huxleyi and Coccolithus pelagicus f. braarudii cultures was assessed using cultivation and cultivation-independent methods. The communities were species rich compared to other phytoplankton cultures. Community analysis identified specific taxa which cooccur in all cultures (Marinobacter and Marivita). Hydrocarbon-degrading bacteria were found in all cultures. The presence of Acidobacteria, Acidimicrobidae, Schlegelella, and Thermomonas was unprecedented but were potentially explained by calcification associated with coccolith production. One strain of Acidobacteria was cultivated and is closely related to a marine Acidobacteria isolated from a sponge. From this assessment of the bacterial diversity of coccolithophores, a number of biotechnological opportunities are evident, from bioprospecting for novel taxa such as Acidobacteria to helping understand the relationship between obligate hydrocarbonoclastic bacteria occurrence with phytoplankton and to revealing bacterial taxa that have a specific association with algae and may be suitable candidates as a means to improve the efficiency of mass algal cultivation.

SUBMITTER: Green DH

PROVIDER: S-EPMC4529885 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Publications

Bacterial Diversity Associated with the Coccolithophorid Algae Emiliania huxleyi and Coccolithus pelagicus f. braarudii.

Green David H DH Echavarri-Bravo Virginia V Brennan Debra D Hart Mark C MC

BioMed research international 20150726

Coccolithophores are unicellular calcifying marine phytoplankton that can form large and conspicuous blooms in the oceans and make significant contributions to oceanic carbon cycling and atmospheric CO2 regulation. Despite their importance, the bacterial diversity associated with these algae has not been explored for ecological or biotechnological reasons. Bacterial membership of Emiliania huxleyi and Coccolithus pelagicus f. braarudii cultures was assessed using cultivation and cultivation-inde ...[more]

PMID: 26273594

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Project description:Emiliania huxleyi is a unicellular micro-alga that forms massive oceanic blooms and plays key roles in global biogeochemical cycles. Mounting studies demonstrate various stimulatory and inhibitory influences that bacteria have on the E. huxleyi physiology. To investigate these algal-bacterial interactions, laboratory co-cultures have been established by us and by others. Owing to these co-cultures, various mechanisms of algal-bacterial interactions have been revealed, many involving bacterial pathogenicity towards algae. However, co-cultures represent a significantly simplified system, lacking the complexity of bacterial communities. In order to investigate bacterial pathogenicity within an ecologically relevant context, it becomes imperative to enhance the microbial complexity of co-culture setups. Phaeobacter inhibens bacteria are known pathogens that cause the death of E. huxleyi algae in laboratory co-culture systems. The bacteria depend on algal exudates for growth, but when algae senesce, bacteria switch to a pathogenic state and induce algal death. Here we investigate whether P. inhibens bacteria can induce algal death in the presence of a complex bacterial community. We show that an E. huxleyi-associated bacterial community protects the alga from the pathogen, although the pathogen occurs within the community. To study how the bacterial community regulates pathogenicity, we reduced the complex bacterial community to a five-member synthetic community (syncom). The syncom is comprised of a single algal host and five isolated bacterial species, which represent major bacterial groups that are naturally associated with E. huxleyi. We discovered that a single bacterial species in the reduced community, Sulfitobacter pontiacus, protects the alga from the pathogen. We further found that algal protection from P. inhibens pathogenicity is a shared trait among several Sulfitobacter species. Algal protection by bacteria might be a common phenomenon with ecological significance, which is overlooked in reduced co-culture systems.

Project description:The hydrogen isotope (2H/1H) ratio of lipids from phytoplankton is a powerful new tool for reconstructing hydroclimate variations in the geologic past from marine and lacustrine sediments. Water 2H/1H changes are reflected in lipid 2H/1H changes with R2 > 0.99, and salinity variations have been shown to cause about a 1‰ change in lipid ?2H values per unit (ppt) change in salinity. Less understood are the effects of growth rate, nutrient limitation and light on 2H/1H fractionation in phytoplankton. Here we present the first published study of growth rate effects on 2H/1H fractionation in the lipids of coccolithophorids grown in continuous cultures. Emiliania huxleyi was cultivated in steady state at four growth rates and the ?2H value of individual alkenones (C37:2, C37:3, C38:2, C38:3), fatty acids (C14:0, C16:0, C18:0), and 24-methyl cholest-5,22-dien-3?-ol (brassicasterol) were measured. 2H/1H fractionation increased in all lipids as growth rate increased by 24‰ to 79‰ (div d-1)-1. We attribute this response to a proportional increase in the fraction of NADPH from Photosystem I (PS1) of photosynthesis relative to NADPH from the cytosolic oxidative pentose phosphate (OPP) pathway in the synthesis of lipids as growth rate increases. A 3-endmember model is presented in which lipid hydrogen comes from NADPH produced in PS1, NADPH produced by OPP, and intracellular water. With published values or best estimates of the fractionation factors for these sources (?PS1 = 0.4, ?OPP = 0.75, and ?H2O = 0) and half of the hydrogen in a lipid derived from water the model indicates ?lipid = 0.79. This value is within the range measured for alkenones (?alkenone = 0.77 to 0.81) and fatty acids (?FA = 0.75 to 0.82) in the chemostat cultures, but is greater than the range for brassicasterol (?brassicasterol = 0.68 to 0.72). The latter is attributed to a greater proportion of hydrogen from NADPH relative to water in isoprenoid lipids. The model successfully explains the increase in 2H/1H fractionation in the sterol 24-methyl-cholesta-5,24(28)-dien-3?-ol from marine centric diatom T. pseudonana chemostat cultures as growth rate increases. Insensitivity of ?FA in those same cultures may be attributable to a larger fraction of hydrogen in fatty acids sourced from intracellular water at the expense of NADPH as growth rate increases. The high sensitivity of ? to growth rate in E. huxleyi lipids and a T. pseudonana sterol implies that any change in growth rate larger than ~0.15 div d-1 can cause a change in ?2Hlipid that is larger than the analytical error of the measurement (~5‰), and needs to be considered when interpreting ?2Hlipid variations in sediments.

Project description:Emiliania huxleyi is a globally abundant microalga that plays a significant role in biogeochemical cycles. Over the next century, sea surface temperatures are predicted to increase drastically, which will likely have significant effects on the survival and ecology of E. huxleyi. In a warming ocean, this microalga may become increasingly vulnerable to pathogens, particularly those with temperature-dependent virulence. Ruegeria is a genus of Rhodobacteraceae whose population size tracks that of E. huxleyi throughout the alga's bloom-bust lifecycle. A representative of this genus, Ruegeria sp. R11, is known to cause bleaching disease in a red macroalga at elevated temperatures. To investigate if the pathogenicity of R11 extends to microalgae, it was co-cultured with several cell types of E. huxleyi near the alga's optimum (18°C), and at an elevated temperature (25°C) known to induce virulence in R11. The algal populations were monitored using flow cytometry and pulse-amplitude modulated fluorometry. Cultures of algae without bacteria remained healthy at 18°C, but lower cell counts in control cultures at 25°C indicated some stress at the elevated temperature. Both the C (coccolith-bearing) and S (scale-bearing swarming) cell types of E. huxleyi experienced a rapid decline resulting in apparent death when co-cultured with R11 at 25°C, but had no effect on N (naked) cell type at either temperature. R11 had no initial negative impact on C and S type E. huxleyi population size or health at 18°C, but caused death in older co-cultures. This differential effect of R11 on its host at 18 and 25°C suggest it is a temperature-enhanced opportunistic pathogen of E. huxleyi. We also detected caspase-like activity in dying C type cells co-cultured with R11, which suggests that programmed cell death plays a role in the death of E. huxleyi triggered by R11 - a mechanism induced by viruses (EhVs) and implicated in E. huxleyi bloom collapse. Given that E. huxleyi has recently been shown to have acquired resistance against EhVs at elevated temperature, bacterial pathogens with temperature-dependent virulence, such as R11, may become much more important in the ecology of E. huxleyi in a warming climate.

Dataset Information

Bacterial Diversity Associated with the Coccolithophorid Algae Emiliania huxleyi and Coccolithus pelagicus f. braarudii.

Publications

Bacterial Diversity Associated with the Coccolithophorid Algae Emiliania huxleyi and Coccolithus pelagicus f. braarudii.

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