Alexandrium: Evolutionary and ecological insights into the most prominent toxigenic dinoflagellate
Dinoflagellates are a major cause of harmful algal blooms, with consequences for coastal marine ecosystem functioning and services. Representatives of Alexandrium tamarense species complex are of the most abundant and widespread toxigenic species, and produces paralytic shellfish poisoning toxins as well as allelochemical substances. This species complex consists of four to five species. The debate of the separation of this complex into real species in long on going and here a concept for the divorce of this group will be proposed. Problems with identification of a toxic member of this species complex in November 2012, which led to the accidental export of toxic mussels to Japan, has now led to severe restrictions on Australian shellfish exports to Japan for a year, and resulting losses of many million $. Furthermore, population genetic insight and adaptive strategies in species interaction processes will be presented. Allelochemical mediated intra-population facilitation, may explain at least partly the high genotypic and phenotypic diversity of Alexandrium populations. Consequently, multiple traits within a population potentially allow mutual facilitation, and may promote the success of microbial planktonic populations.
Insight into the specificity of Wzx for O-antigen processing
Most Gram-negative bacteria have an O antigen that consists of repeats of 3-6 sugars, and serve as an essential factor for host colonization in many disease-causing bacteria. Until now, most known O antigens are assembled by the Wzx/Wzy pathway. This involves the assembly of repeat units within the cytoplasmic face of inner membrane on a lipid carrier, undecaprenol-phosphate, which are translocated across membrane by the Wzx translocases. In the periplasmic face, the repeat units are polymerized by the Wzy polymerase, and then subsequently ligated to preformed lipid A-core in the periplasm. Earlier works have shown Wzx translocases have a relax specificity requirement over the repeat-unit structures. However, this could neither correlate to the presence of O antigen with defined structures in each respective bacteria, nor could it explain the biological diversity of Wzx translocases. Our data show that Wzx translocases have a serotype specificity over their native repeat-unit structures, and provides evidence that the earlier conclusion were obscured by protein overexpression. This provides relevant explanation to the presence of highly diverse, yet structurally defined bacterial surface polysaccharides in nature.
Bridging the gap between ‘omics generated hypotheses and metabolic function of microorganisms in the environment.
Rapid advancements in environmental ‘omics approaches (e.g. metagenomics, transcriptomics, proteomics) have provided a fresh perspective on the metabolic potential of uncultured microorganisms in nature. However, our ability to directly test hypotheses regarding the ecophysiology of microorganisms in their natural environment remains a challenge. New applications of whole cell fluorescence microscopy, stable isotope tracers and nanoscale secondary ion mass spectrometry (FISH-nanoSIMS), provide direct cell-specific isotopic, elemental and phylogenetic information on the metabolic roles of environmental microorganisms and microbial associations. This presentation will introduce the FISH-nanoSIMS method and highlight its utility for the field of microbial ecology through a case study of uncultured methane-consuming archaeal-bacterial symbioses in deep-sea sediments.
Effect of Huanglongbing on the structure and functional diversity of microbial communities associated with citrus.
Plant-microbe interactions lie at the heart of plant performance and ecology. It has been postulated that disruption of multi-trophic interactions in a stable ecosystem under the influence of invading phytopathogens will cause community reorganization and changes in the local feedback interactions. However, there is a paucity of knowledge on the extent to which such community shifts may occur, on the dynamics of changes and on the putative effects regarding the functioning of ecosystems. We have used Citrus-‘Candidatus Liberibacter asiaticus’ [Las, causal agent of devastating Huanglongbing (HLB) disease] as a host pathogen model to characterize the structure, function and interactions of plant-associated microbial communities. We applied a suit of metagenomic techniques to provide detailed census of citrus associated microbiomes. Our results confirmed that Las is the sole causal agent of HLB in Florida and revealed that HLB significantly re-structures the composition of native microbial community present either in leaf, roots and rhizosphere of citrus. Functional microarray (Geochip) and shotgun metagenomic sequencing showed that HLB has severe effects on various functional guilds of bacteria involved in key ecological processes including nitrogen cycling and carbon fixation. Overall, the metagenomic studies provided evidence that change in plant physiology mediated by Las infection could elicit shifts in the composition and functional potential of plant associated microbial communities. In the long term, these fluctuations might have important implications for the productivity and sustainability of citrus producing agro-ecosystems.
January JAMS got the new year off to a good start with a solid turnout and some stimulating talks. First up was Olivier Laczka who took us in to the technical realm of biosensors. Olivier’s work has focused on developing cost-effective tools for the rapid identification of micro-organisms relevant to industry and has led to several Patents.