Revisiting australianectocarpus subulatus(phaeophyceae) from the hopkins river: distribution, abiotic environment, and associated microbiota

Abstract

Ectocarpus is a genus of common marine brown algae. In 1995 a strain of Ectocarpus was isolated from Hopkins River Falls, Victoria, Australia, constituting one of few available freshwater or nearly freshwater brown algae, and the only one belonging to Ectocarpus. It has since been used as a model to study acclimation and adaptation to low salinities and the role of its microbiota in these processes. However, little is known about the distribution of this strain or whether it represents a stable population. Furthermore, its microbiota may have been impacted by the long period of cultivation.Twenty-two years after the original finding we searched for Ectocarpus in the Hopkins River and surrounding areas. We found individuals with ITS and cox1 sequences identical to the original isolate at three sites upstream of Hopkins River Falls, but none at the original isolation site. The osmolarity of the water at these sites ranged from 74-170 mOsmol, and it was rich in sulfate. The diversity of bacteria associated with the algae in situ was approximately one order of magnitude higher than in previous studies of the original laboratory culture, and 95 alga-associated bacterial strains were isolated from E. subulatus filaments on site. In particular, Planctomycetes were abundant in situ but rare in the laboratory-cultured strain.Our results confirm that E. subulatus has stably colonized the Hopkins River, and the newly isolated algal and bacterial strains offer new possibilities to study the adaptation of Ectocarpus to low salinity and its interactions with its microbiome.

Presence of Exogenous Sulfate Is Mandatory for Tip Growth in the Brown Alga Ectocarpus subulatus

“…To assay tolerance to various salinities, cultures were grown in either undiluted (100%) or diluted (10%) seawater. Two E. subulatus strains, Bft15b (present study) and Ec371 ( Dittami et al, 2012 ), are known to generate distinct morphotypes upon salinity variations, suggesting that such morphological changes may constitute a selective advantage during colonization of habitats ( Dittami et al, 2012 ; Dittami et al, 2020a ; Dittami et al, 2020b ).…”

The microbiome of the habitat‐forming brown alga Fucus vesiculosus (Phaeophyceae) has similar cross‐Atlantic structure that reflects past and present drivers1

“…Macroalgae depend upon bacteria for normal morphology (Fucus spiralis, Fries 1977; Ectocarpus sp., Tapia et al 2016; Ulva spp., Fries 1975, Provasoli and Pintner 1980, Singh et al 2011, Ghaderiardakani et al 2017, Alsufyani et al 2020, even becoming unicells when axenic (Matsuo et al 2005). The composition and structure of macroalgal microbiomes vary according to host taxonomy (Longford et al 2007, Lachnit et al 2009, Roth-Schulze et al 2018, host morphology (Lemay et al 2020), environmental gradients (Weigel and Pfister 2019, Dittami et al 2020, Quigley et al 2020, and host tissues (Quigley et al 2018(Quigley et al , 2020, but differ from the water column or adjacent substratum (Lachnit et al 2009, Quigley et al 2020.…”

Ectocarpus: an evo-devo model for the brown algae

“…from Peru and northern Chile (SE Pacific) is the best studied species in the genus, and has become an established model for developmental biology and evolutionary questions (see below). While most species are exclusively marine, some species such as Ectocarpus subulatus may also occur in permanently brackish habitats such as the inner Baltic Sea and has even been encountered in mineral-rich freshwater [3].…”