The role of Rubisco kinetics and pyrenoid morphology in shaping the CCM of haptophyte microalgae.

The haptophyte algae are a cosmopolitan group of primary producers that contribute significantly to the marine carbon cycle and play a major role in paleo-climate studies. Despite their global importance, little is known about carbon assimilation in haptophytes, in particular the kinetics of their Form 1D CO2-fixing enzyme, Rubisco. Here we examine Rubisco properties of three haptophytes with a range of pyrenoid morphologies (Pleurochrysis carterae, Tisochrysis lutea, and Pavlova lutheri) and the diatom Phaeodactylum tricornutum that exhibit contrasting sensitivities to the trade-offs between substrate affinity (Km) and turnover rate (kcat) for both CO2 and O2. The pyrenoid-containing T. lutea and P. carterae showed lower Rubisco content and carboxylation properties (KC and kCcat) comparable with those of Form 1D-containing non-green algae. In contrast, the pyrenoid-lacking P. lutheri produced Rubisco in 3-fold higher amounts, and displayed a Form 1B Rubisco kCcat-KC relationship and increased CO2/O2 specificity that, when modeled in the context of a C3 leaf, supported equivalent rates of photosynthesis to higher plant Rubisco. Correlation between the differing Rubisco properties and the occurrence and localization of pyrenoids with differing intracellular CO2:O2 microenvironments has probably influenced the divergent evolution of Form 1B and 1D Rubisco kinetics.

Adhesion molecules from the diatom Phaeodactylum tricornutum (Bacillariophyceae): genomic identification by amino-acid profiling and in vivo analysis.

Cell adhesion molecules (CAMs) are important in prokaryotes and eukaryotes for cell-cell and cell-substratum interactions. The characteristics of adhesive proteins in the model diatom Phaeodactylum tricornutum were investigated by bioinformatic analysis and in vivo characterization. Bioinformatic analysis of the protein coding potential of the P. tricornutum genome used an amino-acid profile that we developed as a new system to identify uncharacterized or novel CAMs. Putative diatom CAMs were identified and seven were characterized in vivo, by generation of transgenic diatom lines overexpressing genes encoding C-terminal yellow fluorescent protein (YFP) fusion proteins. Three of these selected genes encode proteins with weak similarity to characterized proteins, a c-type lectin and two fasciclins, whereas the others are novel. The resultant cell lines were investigated for alterations in their adhesive ability. Whole cell-substratum adhesion strength was measured in a fully turbulent flow chamber, while atomic force microscopy was used to quantify the relative frequency of adhesion, as well as the length and strength of single molecules in the secreted mucilage. Finally, quartz crystal microbalance analysis characterized the visco-elastic properties and interaction of the mucilage-substratum interface. These combined studies revealed a range of phenotypes affecting adhesion, and led to the identification of candidate proteins involved in diatom adhesion. In summary, our study has for the first time combined bioinformatics and molecular physiological studies to provide new insights into diatom adhesive molecules.

Development of the primary bacterial microfouling layer on antifouling and fouling release coatings in temperate and tropical environments in Eastern Australia.

The role played by bacteria during the pioneering stages of colonisation on marine coatings was investigated over three distinct seasons in both tropical and temperate environments. Novel methods were developed to facilitate the study of the adhered bacterial population on the test coatings in their native, hydrated state. The approach eliminated destructive sample preparation techniques, including sample dehydration and/or removal from the substratum surface prior to analysis. Bacterial colonisation during initial biofilm formation was evaluated on two antifouling paints, Intersmooth 360 and Super Yacht 800, and a fouling release coating, Intersleek 700. Bacterial colonisation was quantified on all three coating surfaces. Intersleek 700 displayed the quickest colonisation by bacteria, resulting in major modification of the substratum surface within 2-4 days following immersion in the ocean. Whilst fouling accumulated more quickly on Intersleek 700, by 16 days all three coatings were fouled significantly. Bacterial fouling was correlated to both location and season, with fouling occurring at a more rapid rate at the Cairns location, as well as during the summer months, when higher water temperatures were recorded. Successful colonisation of all coatings by bacteria soon after immersion modifies the characteristics of the surfaces at the hull/water interface, and subsequent settlement by higher biofouling organisms must be moderated by these modified surfaces.