JAMS October 2012 Report

Maria-Luisa Gutierrez-Zamora

The JAMS rendezvous this October 31st took place in the fourth floor of the Museum with a magnificent view of Sydney, and began with an ad hoc presentation featuring sulphurous scents and sexy fangs. Katherina Petrou (UTS) initiated us in the science of the sulphur cycle in the oceans and how this process is dominated by the production of dimethylsulfoniopropionate (DMSP) by microalgae and its decomposition into dimethylsulphide (DMS), a strong odorous chemoattractant for a range of marine organisms. In tackling the mystery of how harmful algal blooms disappear, Katherina discovered that DMS produced by the dinoflagellate Alexandrium minutum (causative agent of toxic algal blooms) was the chemical cue for the infection of its parasitoid Parvilucifera sinerae.  An elegant video illustrated how DMS at 300 nM was able to activate the parasitoid spores from a dormant state to leave the sporangium (an infected A. minutum cell) in transit to infect other cells and propagate. Activation only occurred in the range of 30 to 300 nM indicating that the effect was dependent on cell density. Thus, Katherina’s work showed that DMS plays an important role in the biological control of toxic algal blooms in the oceans. Her results contribute to the better understanding of marine chemical ecology.

As twilight set in and the bats roamed elegantly in the stunning sky in front of us, Andrew Bisset (CSIRO) enlightened us about the “Priming Effect” in agricultural soils in the context of carbon sequestration. That is, when new carbon (e.g. residual wheat from harvest) is added to the soil, the old more recalcitrant carbon residing in the soil gets a further round of microbial biodegradation, further increasing carbon sequestration. It has been suggested that this process can be enhanced by the addition of mineral nutrients (N, P, S). Interested in this aspect, Andrew conducted microcosm experiments where agricultural soils were amended with 13C-labelled wheat and with or without N+P+S to investigate the changes in microbial communities during carbon sequestration. Respiration, carbon, nitrogen, phosphorous and sulphur transformations were measured over time, and stable isotope probing coupled to Phylochip arrays were used to identify the active microbial communities. Andrew observed that in contrast to the controls, soils amended with nutrients increased in both new and total carbon pools, suggesting that indeed mineral nutrients enhanced C sequestration. The bacterial communities actively involved in carbon decomposition were different for nutrient amended and non-amended treatments, indicating that carbon use efficiency is dependant on the microbial composition too. Interestingly, fungal populations did not show the same trend as bacteria, suggesting a principal role of bacteria in C sequestration from wheat in agricultural soils.

After this talk, we sequestered our own carbon with the now traditional pizza and beer session that followed. Good leg stretching, co-mingling and interesting conversations got us ready for the next talk by Alex de Menezes (CSIRO). Somewhat continuing with the carbon subject, Alex talked about phenanthrene microbial degradation in soils. He studied the who and how of this process not by using stable isotope probing, but by sequencing taxonomic genes as well as expressed functional genes, through mRNA, in phenanthrene amended soils over time. His results showed a marked increase in the abundance of Actinobacteria in amended soils that seemed to have expressed a plethora of stress response genes in addition to dioxygenases, heavy metal P-type ATPases and thioredoxins, suggesting a major role of these bacteria in detoxification of phenanthrene in this soil. Alex designed his own polyaromatic hydrocarbon (PAH) degradation genes database and found that PAH-degradatory gene expression occurred for all the gene groups analysed. Interestingly, an increase in the abundance of amoeba protozoans was concomitant to increases in Actinobacterial populations. Also, expressed genes unique to Amoeba parasites were concurrent with phenanthrene degradation over time. These results seem to suggest that Alex may have discovered an interesting food chain where phenanthrene feeds Actinobacteria, which feed Amoeba, which feed its parasite… and then perhaps die? His novel metatranscriptomic approach was thorough, answered important questions, and opened up new interesting avenues for further research.

Good talks, good food, good drinks, good people. And what a view! JAMS ticks all boxes. Be sure to be there next time.