Genetic indicators of iron limitation in wild populations of Thalassiosira oceanica from the northeast Pacific Ocean

Abstract

Assessing the iron (Fe) nutritional status of natural diatom populations has proven challenging as physiological and molecular responses can differ in diatoms of the same genus. We evaluated expression of genes encoding flavodoxin (FLDA1) and an Fe-starvation induced protein (ISIP3) as indicators of Fe limitation in the marine diatom Thalassiosira oceanica. The specificity of the response to Fe limitation was tested in cultures grown under Fe- and macronutrient-deficient conditions, as well as throughout the diurnal light cycle. Both genes showed a robust and specific response to Fe limitation in laboratory cultures and were detected in small volume samples collected from the northeast Pacific, demonstrating the sensitivity of this method. Overall, FLDA1 and ISIP3 expression was inversely related to Fe concentrations and offered insight into the Fe nutritional health of T. oceanica in the field. As T. oceanica is a species tolerant to low Fe, indications of Fe limitation in T. oceanica populations may serve as a proxy for severe Fe stress in the overall diatom community. At two shallow coastal locations, FLD1A and ISIP3 expression revealed Fe stress in areas where dissolved Fe concentrations were high, demonstrating that this approach may be powerful for identifying regions where Fe supply may not be biologically available.

Community‐Level Responses to Iron Availability in Open Ocean Plankton Ecosystems

“…To assess the reliability of the modeled iron distributions, we correlated the expression of diatom ISIP genes in metatranscriptomics data sets with the annual means of iron concentrations estimated by the DARWIN model, and with annual and monthly means by the PISCES2 model (Carradec et al, ; Table S1a and supporting information S1). These genes have been found in multiple previous studies to be inversely correlated with iron availability (Allen et al, ; Chappell et al, ; Graff van Creveld et al, ; Marchetti et al, ; Morrissey et al, ). Figure presents a comparison between the estimates of dissolved iron concentrations derived from the annual mean iron field from PISCES2 and ECCO2‐DARWIN (Table S1a), with the Tara Oceans stations superimposed and best available estimates based upon in situ measurements (Figure ).…”

The iron limitation mosaic in the California Current System: Factors governing Fe availability in the shelf/near‐shelf region

“…In particular, ISIP3 expression was similar to that of the DFB treatment suggesting the onset of Fe‐stress. These trends are consistent with those observed by Chappell et al () that demonstrated Fe stress in Thalassiosira oceanica in offshore waters close to our region of study using a similar molecular approach.…”

Responses of phytoplankton assemblages to iron availability and mixing water masses during the spring bloom in the Oyashio region, NW Pacific

“…However, our immunological Fd/Fld assay could not be used as a diagnostic of Fe deficiency in micro‐sized diatoms during the spring bloom in the Oyashio region. Recently, Chappell et al () proposed alternative methods for evaluating iron limitation using the genes encoding flavodoxin ( FLDA1 ) and Fe‐starvation induced protein 3 ( ISIP3 ). Marchetti et al () also proposed a new index, the Pseudo‐nitzschia Iron Limitation Index ( Ps‐n ILI), based on a comparative transcriptomic approach using gene sequences of ferritin ( FTN ), encoding the iron storage protein, and iron‐starvation‐induced protein 2a ( ISIP 2a), encoding an iron‐concentrating protein.…”