Diatom-Derived Polyunsaturated Aldehydes Are Unlikely to Influence the Microbiota Composition of Laboratory-Cultured Diatoms

Abstract

Diatom-derived oxylipins, including polyunsaturated aldehydes (PUA), are considered to have infochemical, allelochemical and bacteriostatic properties, with plausible roles as grazing deterrents and regulators of inter- and intraspecific competition. However, the extent and mechanisms of how PUA influence diatom–bacteria interactions remain unresolved. In this study, impacts on the diversity of the associated bacterial communities (microbiota) of two contrasting Skeletonema marinoi strains (a PUA and a non-PUA producer) were investigated under three nitrate conditions in batch culture. Further, the response of the culture microbiota was studied when spiked with PUA at ecologically relevant concentrations (86nM octadienal and 290nM heptadienal). Of the 741 identified OTUs, Proteobacteria was the most abundant phylum (62.10%), followed by Bacteroidetes (12.33%) and Firmicutes (6.11%). Escherichia/Shigella were the most abundant genera for all treatments. Similar communities were present in both spiked and non-spiked cultures suggesting they can tolerate PUA exposure at realistic concentrations. This study suggests that PUA are not major drivers of diatom–bacteria interactions in laboratory cultures.

Polyunsaturated Aldehydes Profile in the Diatom Cyclotella cryptica Is Sensitive to Changes in Its Phycosphere Bacterial Assemblages

“…We did not analyze the diversity of associated microbiota for each experiment. Released PUA could lead to changes in the diversity of the bacterial community for Ncultures and I-cultures, as it has been reported by several authors for coastal bacteria [23], or not, as has been documented by Eastabrook et al [25], for laboratory diatom cultures, but this does not detract from the fact that we found a mutual benefit for growth. We hypothesize that, albeit at nM levels, the PUA released (type and quantity) could contribute to defining a specific organic matter signature of this diatom at each assayed condition.…”

“…Some authors showed differential effects of PUA on the growth and metabolism of natural free-living bacterial communities [22,23], and Edwards et al suggested that PUA altered the community structure of particle-associated bacteria suggesting a role in bacterial community succession [24]. Very recently, Eastabrook et al have suggested that PUA is not the main driver of diatom-bacteria interactions in laboratory cultures [25]. Recent publications also consider the significant role of attached bacteria in phosphorus recycling in nature [26,27].…”

Multiple Roles of Diatom-Derived Oxylipins within Marine Environments and Their Potential Biotechnological Applications

“…Contrary to the results of Edwards et al [ 58 ], the abundance of free bacteria was almost the same at the end of the experiment, suggesting that PUAs did not influence the bacterial community [ 117 ]. Recently, this latter observation was confirmed, since treatments with heptadienal and octadienal on two strains of S. marinoi , a PUA- and a non-PUA producer, showed no significant differences in bacterial communities between the two cultures [ 118 ]. Overall, these contrasting results reinforce the idea, previously suggested by Paul et al [ 115 ], that PUAs could act in a more complex manner, where additional chemical mediators are also involved.…”