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  • 1
    Publication Date: 2019-04-23
    Description: Benthic foraminifera populate a diverse range of marine habitats. Their ability to use alternative electron acceptors—nitrate (NO3−) or oxygen (O2)—makes them important mediators of benthic nitrogen cycling. Nevertheless, the metabolic scaling of the two alternative respiration pathways and the environmental determinants of foraminiferal denitrification rates are yet unknown. We measured denitrification and O2 respiration rates for 10 benthic foraminifer species sampled in the Peruvian oxygen minimum zone (OMZ). Denitrification and O2 respiration rates significantly scale sublinearly with the cell volume. The scaling is lower for O2 respiration than for denitrification, indicating that NO3− metabolism during denitrification is more efficient than O2 metabolism during aerobic respiration in foraminifera from the Peruvian OMZ. The negative correlation of the O2 respiration rate with the surface/volume ratio is steeper than for the denitrification rate. This is likely explained by the presence of an intracellular NO3− storage in denitrifying foraminifera. Furthermore, we observe an increasing mean cell volume of the Peruvian foraminifera, under higher NO3− availability. This suggests that the cell size of denitrifying foraminifera is not limited by O2 but rather by NO3− availability. Based on our findings, we develop a mathematical formulation of foraminiferal cell volume as a predictor of respiration and denitrification rates, which can further constrain foraminiferal biogeochemical cycling in biogeochemical models. Our findings show that NO3− is the preferred electron acceptor in foraminifera from the OMZ, where the foraminiferal contribution to denitrification is governed by the ratio between NO3− and O2.
    Type: Article , PeerReviewed
    Format: text
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  • 2
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Insertional mutagenesis by an IS946-based integration vector (pTRK145) was demonstrated in Lactococcus lactis subsp. lactis. The suicide vector pTRK145 does not replicate in Gram-positive bacteria and, therefore, expression of its erythromycin resistance (Emr) determinant in lactococci requires integration into the bacterial genome. Random integration of pTRK145 in L. lactis MG1363, a Rec+ strain with regions of homology to IS946, was demonstrated by digesting the chromosomal DNA from 20 integrants with EcoRI, which cuts pTRK145 once. Hybridization with a pTRK145-specific probe identified junction fragments which varied in size, indicating random insertion. The utility of pTRK145 was demonstrated by screening integrants for a mutant deficient in maltose utilization (Mal−). A Mal− mutation coincident with pTRK145 integration was isolated. Upon excision of the insert in vivo, the Mal+ Ems phenotype was restored. IS946-based vectors have the potential for development into effective insertional mutagens which may be valuable for localization and cloning of chrosomal genes in lactococci.
    Type of Medium: Electronic Resource
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