Microorganisms living on macroalgae: diversity, interactions, and biotechnological applications

Microorganisms in the environment do not exist as the often-studied pure cultures but as members of complex microbial communities. Characterizing the interactions within microbial communities is essential to understand their function in both natural and engineered environments. In this study, we investigated how the presence of a nitrite-oxidizing bacterium (NOB) and heterotrophic bacteria affect the growth and proteome of the chemolithoautotrophic ammonia-oxidizing bacterium (AOB) Nitrosomonas sp. strain Is79. We investigated Nitrosomonas sp. Is79 in co-culture with Nitrobacter winogradskyi, in co-cultures with selected heterotrophic bacteria, and as a member of the nitrifying enrichment culture G5-7. In batch culture, N. winogradskyi and heterotrophic bacteria had positive effects on the growth of Nitrosomonas sp. Is79. An isobaric tag for relative and absolute quantification (iTRAQ) liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics approach was used to investigate the effect of N. winogradskyi and the co-cultured heterotrophic bacteria from G5-7 on the proteome of Nitrosomonas sp. Is79. In co-culture with N. winogradskyi, several Nitrosomonas sp. Is79 oxidative stress response proteins changed in abundance, with periplasmic proteins increasing and cytoplasmic proteins decreasing in abundance. In the presence of heterotrophic bacteria, the abundance of proteins directly related to the ammonia oxidation pathway increased, while the abundance of proteins related to amino acid synthesis and metabolism decreased. In summary, the proteome of Nitrosomonas sp. Is79 was differentially influenced by the presence of either N. winogradskyi or heterotrophic bacteria. Together, N. winogradskyi and heterotrophic bacteria reduced the oxidative stress for Nitrosomonas sp. Is79, which resulted in more efficient metabolism. IMPORTANCEAerobic ammonia-oxidizing microorganisms play an important role in the global nitrogen cycle, converting ammonia to nitrite. In their natural environment, they coexist and interact with nitrite oxidizers, which convert nitrite to nitrate, and with heterotrophic microorganisms. The presence of nitrite oxidizers and heterotrophic bacteria has a positive influence on the growth of the ammonia oxidizers. Here, we present a study investigating the effect of nitrite oxidizers and heterotrophic bacteria on the proteome of a selected ammonia oxidizer in a defined culture to elucidate how these two groups improve the performance of the ammonia oxidizer. The results show that the presence of a nitrite oxidizer and heterotrophic bacteria reduced the stress for the ammonia oxidizer and resulted in more efficient energy generation. This study contributes to our understanding of microbemicrobe interactions, in particular between ammonia oxidizers and their neighboring microbial community.

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confidence: 99%

“…For example, macro-and microalgae live with specific heterotrophic microbial subcommunities. The exchange of nutrients, enzymes, and bioactive compounds in these communities results in increased community productivity (24,25). AOB have been shown to interact positively with NOB and heterotrophic bacteria (26)(27)(28)(29)(30).…”

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confidence: 99%

Effects of Bacterial Community Members on the Proteome of the Ammonia-Oxidizing Bacterium Nitrosomonas sp. Strain Is79

Sedlacek

Nielsen

Greis

et al. 2016

“…To our knowledge, however, nobody has yet performed functional screening of metagenomic libraries from algal microbial communities. As algal microbial biofilms are in constant interaction with algal biomass, they represent an interesting source of enzymes and other active compounds (18). Sequence-based studies have already revealed the importance and functions of microbial communities living on the surfaces of algae, showing tight interdependence between algae and their biofilms (19)(20)(21).…”

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confidence: 99%

Identification and Characterization of a Halotolerant, Cold-Active Marine Endo-β-1,4-Glucanase by Using Functional Metagenomics of Seaweed-Associated Microbiota

Martin

Biver

Steels

et al. 2014

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A metagenomic library was constructed from microorganisms associated with the brown alga Ascophyllum nodosum. Functional screening of this library revealed 13 novel putative esterase loci and two glycoside hydrolase loci. Sequence and gene cluster analysis showed the wide diversity of the identified enzymes and gave an idea of the microbial populations present during the sample collection period. Lastly, an endo-␤-1,4-glucanase having less than 50% identity to sequences of known cellulases was purified and partially characterized, showing activity at low temperature and after prolonged incubation in concentrated salt solutions. Previous surveys have revealed that less than 1% of existing microorganisms can be studied by traditional culturing methods. This leaves most microorganisms and their by-products unknown and unexploited (1, 2) and explains why metagenomics, a culture-independent approach using total microbial genomes from environmental samples, has met with great success over the past decade (3, 4). Sequence-based metagenomics has already provided information about the composition, organization, function, and hierarchy of microbial communities in particular habitats (5). On the other hand, functional genomics applied to metagenomic libraries from diverse environments has led to the discovery of many new enzymes and bioactive compounds and to substantial enrichment of genome databases. To date, most of the enzymes brought to light through metagenomics have been derived from soil (6-9) and gut (10-13) samples.Marine microorganisms represent promising candidate sources of original biocatalysts, as they are exposed to extreme conditions of temperature, pressure, salinity, nutrient availability, etc. Hence, functional screening of marine microbial populations should yield new enzymes with specific and unique physiological and biochemical properties, produced by organisms far different from those usually described in terrestrial environments (14). New enzymes have already been identified in marine metagenomic libraries from seawater samples (15, 16) and from microorganisms in symbiosis with marine organisms such as sponges and corals (17). To our knowledge, however, nobody has yet performed functional screening of metagenomic libraries from algal microbial communities. As algal microbial biofilms are in constant interaction with algal biomass, they represent an interesting source of enzymes and other active compounds (18). Sequence-based studies have already revealed the importance and functions of microbial communities living on the surfaces of algae, showing tight interdependence between algae and their biofilms (19-21). Furthermore, many genes coding for enzymes involved in hydrolyzing algal biomass, such as cellulases, xylanases, ␣-amylases, and specific algal polysaccharidases (e.g., agarases, carrageenases, and alginate lyases), have been identified from cultivable marine bacteria (22,23). Only a few such enzymes have been found in marine metagenomes by functional screening. For example, no cellulase gene...

“…Among the bacteria known to interact with algae, Flavobacteriia, and notably several species of Zobellia, have been found in association with macroalgae (31)(32)(33) and have been isolated from phytoplankton (34) and from seawater (35). The interactions between Zobellia strains and marine algae range from symbiosis, with some strains inducing the normal differentiation of green macroalgae (36), to algicidal behavior toward dinoflagellate blooms (34).…”

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confidence: 99%

The Mannitol Utilization System of the Marine Bacterium Zobellia galactanivorans

Groisillier

Labourel

Michel

et al. 2015

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Mannitol is a polyol that occurs in a wide range of living organisms, where it fulfills different physiological roles. In particular, mannitol can account for as much as 20 to 30% of the dry weight of brown algae and is likely to be an important source of carbon for marine heterotrophic bacteria. Zobellia galactanivorans (Flavobacteriia) is a model for the study of pathways involved in the degradation of seaweed carbohydrates. Annotation of its genome revealed the presence of genes potentially involved in mannitol catabolism, and we describe here the biochemical characterization of a recombinant mannitol-2-dehydrogenase (M2DH) and a fructokinase (FK). Among the observations, the M2DH of Z. galactanivorans was active as a monomer, did not require metal ions for catalysis, and featured a narrow substrate specificity. The FK characterized was active on fructose and mannose in the presence of a monocation, preferentially K ؉ . Furthermore, the genes coding for these two proteins were adjacent in the genome and were located directly downstream of three loci likely to encode an ATP binding cassette (ABC) transporter complex, suggesting organization into an operon. Gene expression analysis supported this hypothesis and showed the induction of these five genes after culture of Z. galactanivorans in the presence of mannitol as the sole source of carbon. This operon for mannitol catabolism was identified in only 6 genomes of Flavobacteriaceae among the 76 publicly available at the time of the analysis. It is not conserved in all Bacteroidetes; some species contain a predicted mannitol permease instead of a putative ABC transporter complex upstream of M2DH and FK ortholog genes. Brown algae (Phaeophyceae) are the dominant macroalgae in temperate and polar regions and thus play a crucial role in the primary production of coastal ecosystems (1). They contain large amounts of different structural and storage carbohydrates. For instance, their extracellular matrices are formed by the accumulation of cellulose, fucanes, and alginates (2-4), while they store carbon by accumulating laminarin and mannitol (5). The potential of this biomass resource for the production of liquid biofuels (6), including ethanol from alginate and mannitol (7,8), and for the implementation of biorefineries (9) has been highlighted recently.Depending on the species, mannitol can represent as much as 20 to 30% of the dry weight of brown seaweed (10). In the genomic and genetic model of brown algae Ectocarpus sp., formerly included in the species Ectocarpus siliculosus (11), it has been observed that the content of this polyol differs according to the diurnal cycle (12) and that it is likely to act as an osmoprotectant or a local compatible osmolyte (13). Mannitol is localized in the cytosol and is also present at the reducing ends of vacuolar laminarin molecules of the M series (in contrast to the G series, which contain only glucose residues) (14). Mannitol in brown algae is produced directly from the photoassimilate fructose-6-phosphate (F6P) by two st...