4.4.5. Role of CAB in iron fertilisation
Pleuromamma spp. carries a similar proportion of ferric iron reductase gene (fhuF) and ferrous iron transport protein A gene (feoA) (Figure S6a, b). The presence of high proportion of ferric iron reductase gene fhuF in Pleuromamma spp. needs detailed investigation. It was reported that acidic and low-oxygen conditions in copepod gut may assist iron dissolution and remineralisation, forming soluble Fe (II) [13, 67]. Thus, this increases the iron bioavailability in the surrounding, which promotes phytoplankton growth [67]. Also, bacterial community associated with the zooplankton, such as Bacteroidetes, Alphaproteobacteria and Gammaproteobacteria, are known to carry genes involved in iron metabolism [9].
An early study on Thalassiosira pseudonana fed to Acartia tonsa was found to have Fe in the faecal pellets[68]. But, in the present analysis, Acartiaspp. was found to have less proportion of feoA gene when compared toTemora spp. and Pleuromamma spp. Moreover, genes involved in iron metabolism were reported to be high in zooplankton associated microbiome [9].
Since the differential iron contributions of different copepod genera were unknown until now. For organisms that must combat oxygen limitation for their survival (Pleuromamma spp.), pathways for the uptake of ferrous iron are essential. Nevertheless, the meta-analysis performed here showed that Pleuromamma spp. could be a significant contributor to both iron bioavailability and nitrogen fixation.