Bloom-Forming Cyanobacteria Support Copepod Reproduction and Development in the Baltic Sea

Peer reviewe

Acute kidney injury in patients treated with immune checkpoint inhibitors

Background: Immune checkpoint inhibitor-associated acute kidney injury (ICPi-AKI) has emerged as an important toxicity among patients with cancer. Methods: We collected data on 429 patients with ICPi-AKI and 429 control patients who received ICPis contemporaneously but who did not develop ICPi-AKI from 30 sites in 10 countries. Multivariable logistic regression was used to identify predictors of ICPi-AKI and its recovery. A multivariable Cox model was used to estimate the effect of ICPi rechallenge versus no rechallenge on survival following ICPi-AKI. Results: ICPi-AKI occurred at a median of 16 weeks (IQR 8-32) following ICPi initiation. Lower baseline estimated glomerular filtration rate, proton pump inhibitor (PPI) use, and extrarenal immune-related adverse events (irAEs) were each associated with a higher risk of ICPi-AKI. Acute tubulointerstitial nephritis was the most common lesion on kidney biopsy (125/151 biopsied patients [82.7%]). Renal recovery occurred in 276 patients (64.3%) at a median of 7 weeks (IQR 3-10) following ICPi-AKI. Treatment with corticosteroids within 14 days following ICPi-AKI diagnosis was associated with higher odds of renal recovery (adjusted OR 2.64; 95% CI 1.58 to 4.41). Among patients treated with corticosteroids, early initiation of corticosteroids (within 3 days of ICPi-AKI) was associated with a higher odds of renal recovery compared with later initiation (more than 3 days following ICPi-AKI) (adjusted OR 2.09; 95% CI 1.16 to 3.79). Of 121 patients rechallenged, 20 (16.5%) developed recurrent ICPi-AKI. There was no difference in survival among patients rechallenged versus those not rechallenged following ICPi-AKI. Conclusions: Patients who developed ICPi-AKI were more likely to have impaired renal function at baseline, use a PPI, and have extrarenal irAEs. Two-thirds of patients had renal recovery following ICPi-AKI. Treatment with corticosteroids was associated with improved renal recovery

Trophic complexity of zooplankton–cyanobacteria interactions in the Baltic Sea : Insights from molecular diet analysis

Blooms of nitrogen fixing cyanobacteria (NFC) occur in many freshwater and marine systems, including the Baltic Sea. By fixing dissolved nitrogen, they circumvent general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for non-diazotrophic primary producers and ultimately supporting secondary production. Elucidating trophic links between primary consumers and NFC is essential for understanding role of these blooms for secondary production. However, until recently, there was no reliable method to quantify individual prey species for zooplankter feeding in situ. The development of PCR-based methods to detect prey-specific DNA in the diet of consumers, including microscopic animals, allows identification and quantification of trophic linkages in the field. Using molecular diet analysis in combination with egg production measurements, biochemical markers of growth and condition; and stable isotope approach, we explored a possibility to determine (1) whether cyanobacteria are grazed and assimilated by mesozooplankters (Papers I and II), (2) which species/groups are particularly efficient consumers of cyanobacteria (Papers II and III), and (3) how feeding on cyanobacteria affects zooplankton growth and development (Paper I and III). Taken together, these laboratory and field observations, provided evidence that NFC contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment for the copepod nauplii (Paper I). The favorable growth conditions for juvenile copepods observed during NFC blooms were hypothesized to be mediated by picoplankton that take up bioavailable nitrogen exuded from cyanobacterial cells. This hypothesis found support in Paper II that provided quantitative estimates for the direct picocyanobacteria → mesozooplankton pathway, with highest weight-specific consumption observed in nauplii. Further, using field observations on zooplankton and phytoplankton development during a growth season in the northern Baltic proper, we found that NFC nitrogen is assimilated and transferred to zooplankton via both direct grazing and indirectly through grazing on small-sized phyto- and bacterioplankton (Paper III). Finally, these and other findings emphasizing the importance of NFC for Baltic Sea secondary production during growth season were synthesized to show that diazotrophic nitrogen enters food webs already at bloom initiation (Paper III) and is transferred via multiple pathways to pelagic and benthic food webs and, ultimately, to fish (Paper IV).At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted.</p

Mesozooplankton Grazing on Picocyanobacteria in the Baltic Sea as Inferred from Molecular Diet Analysis

<div><p>Our current knowledge on the microbial component of zooplankton diet is limited, and it is generally assumed that bacteria-sized prey is not directly consumed by most mesozooplankton grazers in the marine food webs. We questioned this assumption and conducted field and laboratory studies to examine picocyanobacteria contribution to the diets of Baltic Sea zooplankton, including copepods. First, qPCR targeting ITS-1 rDNA sequence of the picocyanobacteria <i>Synechococcus</i> spp. was used to examine picocyanobacterial DNA occurrence in the guts of Baltic zooplankton (copepods, cladocerans and rotifers). All field-collected zooplankton were found to consume picocyanobacteria in substantial quantities. In terms of <i>Synechococcus</i> quantity, the individual gut content was highest in cladocerans, whereas biomass-specific gut content was highest in rotifers and copepod nauplii. Moreover, the gut content in copepods was positively related to the picocyanobacteria abundance and negatively to the total phytoplankton abundance in the water column at the time of sampling. This indicates that increased availability of picocyanobacteria resulted in the increased intake of this prey and that copepods may rely more on picoplankton when food in the preferred size range declines. Second, a feeding experiments with a laboratory reared copepod <i>Acartia tonsa</i> fed a mixture of the picocyanobacterium <i>Synechococcus bacillaris</i> and microalga <i>Rhodomonas salina</i> confirmed that copepods ingested <i>Synechococcus</i>, even when the alternative food was plentiful. Finally, palatability of the picocyanobacteria for <i>A. tonsa</i> was demonstrated using uptake of ¹³C by the copepods as a proxy for carbon uptake in feeding experiment with ¹³C-labeled <i>S. bacillaris</i>. These findings suggest that, if abundant, picoplankton may become an important component of mesozooplankton diet, which needs to be accounted for in food web models and productivity assessments.</p></div

Carbon uptake from ¹³C-labeled <i>Synechococcus bacillaris</i> by the copepod <i>Acartia tonsa</i> (live and dead individuals) exposed to the picocyanobacterium (Experiment III).

<p>Carbon uptake is expressed as change in δ¹³C of the copepods from the start values. Differences between the start and each treatment group are shown by asterisks (*: p<0.05; ***: p<0.0001). Data are shown as mean ± SD, <i>n</i> = 3 in all cases.</p

Occurrence of <i>Synechococcus</i> spp. in field-collected zooplankton.

<p>Individual gut content (GC; prey ITS-1 copies ×10³ ind⁻¹) and size-specific gut content (ssGC; prey ITS-1 copies ×10³ µgWW⁻¹) in main zooplankton groups: copepods (adults and older copepodites of <i>Acartia</i> spp. and <i>Eurytemora affinis</i>), cladocerans (<i>Bosmina maritima</i> and <i>Podon</i> spp.) and microzooplankton (rotifers <i>Synchaeta</i> spp., <i>Keratella quadrata</i>, and <i>K. cochlearis</i>, and copepod nauplii). Data are shown as mean ± SD, number of samples is given below the group name.</p

Statistical summary of the generalized linear model examining effects of <i>Synechococcus</i> abundance (ITS-1 copies ×10³ ml) ⁻¹ and total phytoplankton (>2 µm) biovolume (mm³ ml⁻¹) in the water column (0–14 m) on the abundance of <i>Synechococcus</i> DNA in copepod stomachs (ITS-1 copies ×10³ ind⁻¹).

<p>Data are Box-Cox transformed, significant effects are in bold face.</p

<i>Synechococcus</i> abundance (ITS-1 copies ×10³ ind⁻¹) detected in different mesozooplankton species/groups.

<p>Field-collected samples were used for the analysis. <i>E. affinis</i> – <i>Eurytemora affinis</i>, <i>Acartia</i> spp. – <i>Acartia bifilosa</i> and <i>A. longiremis</i>, <i>B. maritima</i> – <i>Bosmina maritima</i>, podonids – <i>P. intermedius</i> and <i>P. leuckartii</i>, rotifers – <i>Synchaeta</i> spp., <i>Keratella cochlearis</i> and K. <i>quadrata</i>; nauplii – <i>Acartia</i> spp. and <i>E. affinis</i>; <i>n</i> – number of samples analyzed.</p

Quantities of <i>Synechococcus bacillaris</i> (ITS-1 copies ×10³ ind⁻¹and cells ×10³ ind⁻¹) detected in the live and dead individuals of the copepod <i>Acartia tonsa</i> (adults and nauplii) exposed to the picocyanobacterium in the feeding experiments (Experiments I and II).

<p>Data are shown as mean ± SD, <i>n</i> = 3 in all cases.</p

Mercury-methylating bacteria are associatedwith copepods: A proof-of-principle survey inthe Baltic Sea

Methylmercury (MeHg) is a potent neurotoxin that biomagnifies in marine food webs. Inorganicmercury (Hg) methylation is conducted by heterotrophic bacteria inhabiting sedimentor settling detritus, but endogenous methylation by the gut microbiome of animals in thelower food webs is another possible source. We examined the occurrence of the bacterialgene (hgcA), required for Hg methylation, in the guts of dominant zooplankters in the NorthernBaltic Sea. A qPCR assay targeting the hgcA sequence in three main clades (Deltaproteobacteria,Firmicutes and Archaea) was used in the field-collected specimens ofcopepods (Acartia bifilosa, Eurytemora affinis, Pseudocalanus acuspes and Limnocalanusmacrurus) and cladocerans (Bosmina coregoni maritima and Cercopagis pengoi). All copepodswere found to carry hgcA genes in their gut microbiome, whereas no amplification wasrecorded in the cladocerans. In the copepods, hgcA genes belonging to only Deltaproteobacteriaand Firmicutes were detected. These findings suggest a possibility that endogenousHg methylation occurs in zooplankton and may contribute to seasonal, spatial andvertical MeHg variability in the water column and food webs. Additional molecular and metagenomicsstudies are needed to identify bacteria carrying hgcA genes and improve theirquantification in microbiota