Transcriptomic responses to iron bioavailability from virus-mediated lysates in marine prokaryotes

Previous studies have demonstrated that the iron content in marine heterotrophic bacteria is comparatively higher than that of phytoplankton. Therefore, they have been indicated to play a major role in the biogeochemical cycling of iron. In this study, we aimed to investigate the potential of viral lysis as a source of iron for marine heterotrophic bacteria. Viral lysates were derived from the marine heterotrophic bacterium, Vibrio natriegens PWH3a (A.K.A Vibrio alginolyticus). The bioavailability of Fe in the lysates was determined using a model heterotrophic bacterium, namely, Dokdonia sp. strain Dokd-P16, isolated from Fe-limited waters along Line P transect in the Northeastern Pacific Ocean. The bacteria were grown under Fe-deplete or Fe-replete conditions before being exposed to the viral lysate. Differential gene expression following exposure to the viral lysate was analyzed via RNA sequencing to identify differentially expressed genes under iron-replete and iron-deplete conditions. This study would provide novel insights into the role of viral lysis in heterotrophic bacteria in supplying bioavailable iron to other marine microorganisms under iron-limiting and non-limiting conditions. First, the marine heterotrophic bacterium genome, Dokdonia sp. strain Dokd-P16, was sequenced to provide a genomic context for the expression studies. Subsequently, the relative gene expression in Dokdonia sp. strain Dokd-P16 grown under Fe limiting and non-limiting conditions were analyzed. This transcriptomic approach would be utilized to elucidate genes regulated by Fe availability in Dokdonia sp. strain Dokd-P16, which indicate its Fe-related response viral lysate exposure. Taken together, in this study, the transcriptomic responses of Fe-limited and non-limited marine heterotrophic bacteria were analyzed, which provided novel insights into the biological availability of Fe from the viral lysates. Overall design: Samples grown under either Fe-deplete or Fe-replete conditions then exposed with either viral lysate (L) media control (AQUIL) for five different exposure times (T0,T1,T2,T3,T4). An additional control with nothing added (NOADD) is also included and sampled at two different time points (Tm,Tend). All combinations of Fe condition, exposure and time were replicated five times for a grand total 120 samples (2 Fe conditions X 2 exposures X 5 time points + 2 Fe conditions X 1 exposure X 2 time points).