Synchrotron based FTIR macromolecule profiles of 5 diatom species from the AAS_4026 ocean acidification project. Data represent the peak areas for wavenumbers related to key macromolecules. For details on methods see Duncan et al. (2021) New Phytologist. Experimental design and mesocosm set up Mesocosm set up and conditions were as described previously (Deppeler et al., 2018; Hancock et al., 2018). Briefly, a near-shore, natural Antarctic microbial community was collected from an ice-free area among broken fast ice approximately 1km offshore from Davis Station, Antarctica (68° 35ʹ S, 77° 58ʹ E) on 19 November 2014. This community was incubated in 6 x 650L polyurethane tanks (mesocosms) across a gradient of fCO2 levels (343, 506, 634, 953, 1140 and 1641 μatm; denoted M1 – M6). These fCO2 levels corresponded to pH values ranging from 8.17 to 7.57. Temperature was maintained at 0.0 °C ± 0.5 °C and the mesocosms were stirred continuously by a central auger (15 r.p.m.) for gentle mixing and covered with an air-tight lid. Irradiance was initially kept low (0.8 ± 0.2 μmol photons m-2s-1), while cell physiology was left to acclimate to increasing fCO2 levels (over 5 days). When target fCO2 levels were reached in all six mesocosms, light was gradually increased (days 5-8) to 89 ± 16 μmol photons m-2s-1 on a 19 h:5 h light:dark cycle, to mimic current natural conditions. To generate the gradient in carbonate chemistry, filtered seawater saturated with CO2 was added to five of the mesocosms. Daily measurements were taken to monitor pH and dissolved inorganic carbon (DIC). For details of fCO2 manipulations, analytical procedures and calculations see Deppeler et al., (2018). Samples for physiological and macromolecular measurements in this study were taken on day 18, at the end of the incubation period (Deppeler et al., 2018). Cell volume Cell volume was determined for selected taxa from M1 and M6 via light microscopy. Cells were imaged on a calibrated microscope (Nikon Eclipse Ci-L, Japan) and length, width and height (24-77 cells per taxa) determined using ImageJ software (Schneider et al., 2012). Biovolume was then calculated according to the cell morphology and corresponding equations described by Hillebrand et al (1999). Macromolecular content by FTIR The macromolecular composition of the selected diatom taxa sampled from all six mesocosms on day 18 was determined using Synchrotron based FTIR microspectroscopy on formalin-fixed (2% v/v final concentration) cells. Measurements were made on hydrated cells and processed according to previous studies (Sackett et al. 2103; 2014; Sheehan et al. 2020). Briefly, fixed cells were loaded directly onto a micro-compression cell with a 0.3 mm thick CaF2 window. Spectral data of individual cells (between 15-49 cells per taxon per mesocosm) were collected in transmission mode, using the Infrared Microspectroscopy Beamline at the Australian Synchrotron, Melbourne, in November 2015. Spectra were acquired over the measurement range 4000− 800 cm−1 with a Vertex 80v FTIR spectrometer (Bruker Optics) in conjunction with an IR microscope (Hyperion 2000, Bruker) fitted with a mercury cadmium telluride detector cooled with liquid nitrogen. Co-added interferograms (n = 64) were collected at a wavenumber resolution of 6 cm−1s. To allow for measurements of individual cells, all measurements were made in transmission mode, using a measuring area aperture size of 5 × 5 µm. Spectral acquisition and instrument control were achieved using Opus 6.5 software (Bruker). Normalised spectra of biologically relevant regions revealed absorbance bands representative of key macromolecules were selected. Specifically, the amide II (~1540 cm-1), Free Amino Acid (~1452 cm-1), Carboxylates (~1375 cm-1), Ester carbonyl from lipids (~1745 cm-1) and Saturated Fatty Acids (~2920 cm-1) bands were selected. Infra-red spectral data were analysed using custom made scripts in R (R Development Core Team 2018). The regions of 3050-2800, 1770-1100 cm-1, which contain the major biological were selected for analysis. Spectral data were smoothed (4 pts either side) and second derivative (3rd order polynomial) transformed using the Savitzky-Golay algorithm from the prospectr package in R (Stevens and Ramirez-Lopez, 2014) and then normalised using the method of Single Normal Variate (SNV). Macromolecular content for individual taxon was estimated based on integrating the area under each assigned peak, providing metabolite content according to the Beer-Lambert Law, which assumes a direct relationship between absorbance and relative analyte concentration (Wagner et al., 2010). Integrated peak areas provide relative changes in macromolecular content between samples. Because of the differences in absorption properties of macromolecules, peak areas can only be used as relative measure within compounds.

Exopolysaccharide (EPS) is complex sugar made by many microbes in the Antarctic marine environment. This project seeks to understand the ecological role of microbial EPS in the Southern Ocean, where it is known to strongly influence primary production. We will investigate the chemical composition and structure of EPS obtained from Antarctic microbes, which will improve our knowledge of its ecological significance and biotechnological potential. Dataset includes the following: 1) Information on Exopolysaccharide-producing bacterial isolates, isolation sites, media used and growth conditions. 2) 16S rRNA gene sequence and fatty acid data of isolates for strain identification. 3) Exopolysaccharide chemistry data including EPS carbohydrate composition, organic acid composition, sulfate content, molecular weight. 4) Physiology of exopolysaccharide synthesis. Effects of temperature and other factors on EPS yield and glucose conversion efficiency. 5) Iron binding properties. The download file includes: 11 files File 1. Bacterial isolate 16S rRNA gene sequences obtained from Southern Ocean seawater or ice samples. The sequences are all deposited on the GenBank nucleotide (NCBI) database. Sequences are in FASTA format. File 2. Seawater and sea-ice sample information including sites samples, sample type. File 3. Data for exopolysaccharide (EPS)-producing bacteria isolated and subsequently selected for further studied. Information indicates special treatments used to obtain strains including plankton towing, filtration method, and enrichment. Identification to species level was determined by 16S rRNA gene sequence analysis. File 4. EPS-producing bacterial isolate fatty acid content determined using GC/MS procedures. File 5. Basic chemical data for EPS from Antarctic isolates including protein, sulfate, and sugar type relative content (determined by chemical procedures), molecular weight in kilodaltons and polydispersity (determined by gel-based molecular seiving). File 6 Monosaccharide unit composition determined by GC/MS of EPS from Antarctic isolates. File 7. Effect of temperature on culture viscosity and growth of EPS-producing bacterium Pseudoalteromonas sp. CAM025 as affected by temperature. File 8. Effect of temperature on EPS and cell yields and EPS synthesis efficiency (as indicated by glucose consumption) of EPS-producing bacterium Pseudoalteromonas sp. CAM025 as affected by temperature. File 9. Efficiency of copper and cadmium metal ion adsorption onto EPS from EPS-producing bacterium Pseudoalteromonas sp. CAM025. File 10. Phenotypic characteristics data for novel EPS-producing Antarctic strain CAM030. Represents type strain of Olleya marilimosa. File 11. Effect of temperature on chemical make up of EPS from EPS-producing bacterium Pseudoalteromonas sp. CAM025.