5 research outputs found
Unexpected presence of the nitrogen-fixing symbiotic cyanobacterium UCYN-A in Monterey Bay, California
In the last decade, the known biogeography of
nitrogen fixation in the ocean has been expanded to
colder and nitrogen-rich coastal environments. The
symbiotic nitrogen-fixing cyanobacteria group A
(UCYN-A) has been revealed as one of the most
abundant and widespread nitrogen-fixers, and
includes several sublineages that live associated with
genetically distinct but closely related
prymnesiophyte hosts. The UCYN-A1 sublineage is
associated with an open ocean picoplanktonic
prymnesiophyte, whereas UCYN-A2 is associated with
the coastal nanoplanktonic coccolithophore
Braarudosphaera bigelowii, suggesting that different
sublineages may be adapted to different
environments. Here, we study the diversity of nifH
genes present at the Santa Cruz Municipal Wharf in
the Monterey Bay (MB), California, and report for
the first time the presence of multiple UCYN-A
sublineages, unexpectedly dominated by the UCYNA2 sublineage. Sequence and quantitative PCR data
over an 8-year time-series (2011–2018) showed a shift
toward increasing UCYN-A2 abundances after 2013,
and a marked seasonality for this sublineage which
was present during summer-fall months, coinciding
with the upwelling-relaxation period in the MB.
Increased abundances corresponded to positive
temperature anomalies in MB, and we discuss the
possibility of a benthic life stage of the associated
coccolithophore host to explain the seasonal pattern.
The dominance of UCYN-A2 in coastal waters of the
MB underscores the need to further explore the
habitat preference of the different sublineages in
order to provide additional support for the
hypothesis that UCYN-A1 and UCYN-A2 sublineages
are different ecotypes
Unexpected Presence of the Nitrogen-fixing Symbiotic Cyanobacterium UCYN-A in Coastal Monterey Bay Waters
Cell-specific measurements show nitrogen fixation by particle-attached putative non-cyanobacterial diazotrophs in the North Pacific Subtropical Gyre.
Biological nitrogen fixation is a major important source of nitrogen for low-nutrient surface oceanic waters. Nitrogen-fixing (diazotrophic) cyanobacteria are believed to be the primary contributors to this process, but the contribution of non-cyanobacterial diazotrophic organisms in oxygenated surface water, while hypothesized to be important, has yet to be demonstrated. In this study, we used simultaneous 15N-dinitrogen and 13C-bicarbonate incubations combined with nanoscale secondary ion mass spectrometry analysis to screen tens of thousands of mostly particle-associated, cell-like regions of interest collected from the North Pacific Subtropical Gyre. These dual isotope incubations allow us to distinguish between non-cyanobacterial and cyanobacterial nitrogen-fixing microorganisms and to measure putative cell-specific nitrogen fixation rates. With this approach, we detect nitrogen fixation by putative non-cyanobacterial diazotrophs in the oxygenated surface ocean, which are associated with organic-rich particles (<210 µm size fraction) at two out of seven locations sampled. When present, up to 4.1% of the analyzed particles contain at least one active putative non-cyanobacterial diazotroph. The putative non-cyanobacterial diazotroph nitrogen fixation rates (0.76 ± 1.60 fmol N cell-1 d-1) suggest that these organisms are capable of fixing dinitrogen in oxygenated surface water, at least when attached to particles, and may contribute to oceanic nitrogen fixation
A microarray for assessing transcription from pelagic marine microbial taxa
Metagenomic approaches have revealed unprecedented genetic diversity within microbial communities across vast expanses of the world’s oceans. Linking this genetic diversity with key metabolic and cellular activities of microbial assemblages is a fundamental challenge. Here we report on a collaborative effort to design MicroTOOLs (Microbiological Targets for Ocean Observing Laboratories), a high-density oligonucleotide microarray that targets functional genes of diverse taxa in pelagic and coastal marine microbial communities. MicroTOOLs integrates nucleotide sequence information from disparate data types: genomes, PCR-amplicons, metagenomes, and metatranscriptomes. It targets 19?400 unique sequences over 145 different genes that are relevant to stress responses and microbial metabolism across the three domains of life and viruses. MicroTOOLs was used in a proof-of-concept experiment that compared the functional responses of microbial communities following Fe and P enrichments of surface water samples from the North Pacific Subtropical Gyre. We detected transcription of 68% of the gene targets across major taxonomic groups, and the pattern of transcription indicated relief from Fe limitation and transition to N limitation in some taxa. Prochlorococcus (eHLI), Synechococcus (sub-cluster 5.3) and Alphaproteobacteria SAR11 clade (HIMB59) showed the strongest responses to the Fe enrichment. In addition, members of uncharacterized lineages also responded. The MicroTOOLs microarray provides a robust tool for comprehensive characterization of major functional groups of microbes in the open ocean, and the design can be easily amended for specific environments and research questions