Algal bioactive compounds reduce net oxygen fluxes of artificial diatom biofilms

Abstract

A wide range of chemicals are exuded by microalgae or released by grazed cells. In biofilms, these bioactive compounds may potentially exert a large effect on growing cells, since the cellular density is high and intercellular distances are short. We studied whether such compounds affect the functioning of the biofilm and, therefore, we tested several compounds. These included eicosapentaenoic acid (EPA) and 2E, 4E-decadienal (DD), which are produced during grazing on diatoms. In addition, we obtained a mixture of compounds by methanolic extraction of the allelopathic green alga Uronema confervicolum. We studied how the net oxygen production rates of an artificial diatom biofilm were affected by the different compounds. The extracts of U. confervicolum significantly reduced these rates. Unexpectedly, EPA had a strong effect on the oxygen production rates in the biofilm. A toxic effect was also observed in ecotoxicological assays with the diatom Nitzschia palea. However, the inhibitory effect of DD on the biofilm was weaker than that of EPA, while DD was shown to be more toxic in liquid culture. This differential effect on liquid culture and biofilms indicates that the organization of benthic algae in biofilm should be considered when studying chemical interactions between these organisms.

Chemical interactions in diatoms: role of polyunsaturated aldehydes and precursors

“…This may be counteracted by the fact that PUAs are directly produced inside the digestive tract of grazers (Wichard et al, 2008). Interestingly, although data on freshwater micro-algae are scarce, they seem to be less sensitive to PUAs than do marine micro-algae (Adolph et al, 2004;Leflaive et al, 2008). For all the phototrophic organisms tested, the observed effects of PUAs were similar to apoptosis, as described for animals (Ianora et al, 2004;Poulet et al, 2007a).…”

“…Interestingly, although data on freshwater micro‐algae are scarce, they seem to be less sensitive to PUAs than do marine micro‐algae (Adolph et al. , 2004; Leflaive et al. , 2008).…”

Allelopathic interactions involving benthic phototrophic microorganisms

“…Interspecific chemical interactions in diatoms have been poorly studied despite their diversity and abundance in all aquatic habitats. However, recent studies have revealed that allelochemicals from benthic diatoms are diverse: eicosapentaenoic acid, a polyunsatured fatty acid and 2E,4E-decadienal, a polyunsaturated aldehyde (Leflaive et al 2008a;Leflaive and Ten-Hage, 2009), polyphenolic compounds (Pouvreau et al, 2007), cyanogen bromide (BrCN) a halogenated compound (Vanelslander et al, 2012). All these compounds are produced by benthic diatoms and target co-occurring benthic diatoms.…”

Impairment of benthic diatom adhesion and photosynthetic activity by allelopathic compounds from a green alga: involvement of free fatty acids?

“…Colony formation was expected to provoke higher sedimentation rates (Lürling and Van Donk 2000) and thus lower shading effects. These extracts could also inhibit or decrease the growth and the photosynthetic activity of benthic/epiphytic algae, such as the diatom Nitzschia palea (Leflaive et al 2008b;Leflaive and Ten-Hage 2009). The production of allelopathic compounds by U. confervicolum was controlled by intrinsic (growth phase) and extrinsic (light, nutrients) factors.…”