Bacteria-induced morphogenesis of Ulva intestinalis and Ulva mutabilis (Chlorophyta): a contribution to the lottery theory

Fatemeh Ghaderiardakani,Juliet C Coates,Thomas Wichard

doi:10.1093/femsec/fix094

Fatemeh Ghaderiardakani, Juliet C Coates + Show 1 more

Open Access

https://doi.org/10.1093/femsec/fix094

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Abstract

The green marine macroalgae of the class Ulvophyceae (Ulvophytes) are common algae distributed worldwide particularly in intertidal areas, which play a key role in aquatic ecosystems. They are potentially valuable resources for food, animal feed and fuel but can also cause massive nuisance blooms. Members of Ulvaceae, like many other seaweeds, harbour a rich diversity of epiphytic bacteria with functions related to host growth and morphological development. In the absence of appropriate bacterially derived signals, germ cells of the genus Ulva develop into ‘atypical’ colonies consisting of undifferentiated cells with abnormal cell walls. This paper examines the specificity of bacteria-induced morphogenesis in Ulva, by cross-testing bacteria isolated from several Ulva species on two Ulva species, the emerging model system Ulva mutabilis and the prominent biofouler species Ulva intestinalis. We show that pairs of bacterial strains isolated from species other than U. mutabilis and U. intestinalis can fully rescue axenic plantlets generated either from U. mutabilis or U. intestinalis gametes. This laboratory-based study demonstrates that different compositions of microbial communities with similar functional characteristics can enable complete algal morphogenesis and thus supports the ‘competitive lottery’ theory for how symbiotic bacteria drive algal development.

Highlights

Macroscopic marine algae are significant primary producers in the oceans, which cover about 71% of earth’s surface
This study reports on a cross-testing of potentially morphogenesis-inducing bacteria, isolated from various Ulva species, between the model system U. mutabilis and U. intestinalis
As demonstrated by Spoerner et al, (2012), axenic U. mutabilis plants develop a characteristic morphology with a lack of holdfast and distortions of the exterior cell wall (Fig. 1)

Summary

Introduction

Macroscopic marine algae (seaweeds) are significant primary producers in the oceans, which cover about 71% of earth’s surface. Seaweeds are important for maintaining local biodiversity (Schiel et al, 2007), create a protective environment for numerous invertebrate species (Wilson et al, 1990; Bulleri et al, 2002) and provide an essential habitat for a range of epibionts, from microscopic organisms to macroinvertebrates (Fraschetti et al, 2006). Seaweeds can cause significant nuisance blooms due to eutrophication in shallow coastal areas, which are detrimental to the environment and can harm ecosystems (Smetacek et al., 2013). A number of studies have shown that different species of seaweeds growing in the same ecosystem are associated with species-specific bacterial strains (Lachnit et al, 2009; Barott et al, 2011; Lachnit et al, 2011), leading to the hypothesis that the association between microorganisms and algae is host-specific

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