Algae–bacteria interactions: Evolution, ecology and emerging applications

Abstract

Algae and bacteria have coexisted ever since the early stages of evolution. This coevolution has revolutionized life on earth in many aspects. Algae and bacteria together influence ecosystems as varied as deep seas to lichens and represent all conceivable modes of interactions - from mutualism to parasitism. Several studies have shown that algae and bacteria synergistically affect each other's physiology and metabolism, a classic case being algae-roseobacter interaction. These interactions are ubiquitous and define the primary productivity in most ecosystems. In recent years, algae have received much attention for industrial exploitation but their interaction with bacteria is often considered a contamination during commercialization. A few recent studies have shown that bacteria not only enhance algal growth but also help in flocculation, both essential processes in algal biotechnology. Hence, there is a need to understand these interactions from an evolutionary and ecological standpoint, and integrate this understanding for industrial use. Here we reflect on the diversity of such relationships and their associated mechanisms, as well as the habitats that they mutually influence. This review also outlines the role of these interactions in key evolutionary events such as endosymbiosis, besides their ecological role in biogeochemical cycles. Finally, we focus on extending such studies on algal-bacterial interactions to various environmental and bio-technological applications.

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

“…Recent investigations into nutrient-removal pathways have provided the necessary knowledge for understanding nutrient removal by assimilation, anaerobic ammonia oxidation, nitrification and denitrification (Renuka et al, 2013;van Kessel et al, 2015;Santoro, 2016). Understanding of the complex interactions between attached microalgae and bacteria is pointing out how cooperative interactions allow for functionally stable consortium (Borowitzka, 2016;Ramanan et al, 2016). Besides, the increasing implementation of photobioreactors using attached microalgaebacteria consortium, such as Algal Turf Scrubbers (ATS) (Adey et al, 2013), tank photobioreactors (Su et al, 2011) and tubular biofilm photobioreactor (De Godos et al, 2009), are delivering valuable information about nutrient removal at low concentrations.…”

“…Meanwhile, bacteria decompose organic matter into mineral form and secrete extracellular metabolites such as auxins and vitamin B 12 , which are essential for microalgal growth (Fig. 2a) (Ramanan et al, 2016). Roeselers et al (2007) reported that substrate precolonization by Betaproteobacteria accelerated the growth and adhesion of Microcoleus vaginatus to polycarbonate surfaces.…”

“…Allelochemicals produced by microalgae can exhibit negative effects on the growth of co-cultivated microalgal species, especially under nutrient limited conditions (Borowitzka, 2016;Gonçalves et al, 2017). Overall, competitive interactions between different groups of attached microalgae-bacteria consortium are mechanisms to regulate the consortium structure and response to the external conditions (Ramanan et al, 2016).…”

Effect of bacteria on growth and biochemical composition of two benthic diatoms Halamphora coffeaeformis and Entomoneis paludosa

“…For example, the Roseobacter -algae interaction is well known in marine ecosystems (Geng and Belas, 2010). Members of the Rhodobacteraceae (alphaproteobacteria) play an important role in carbon and sulphur biogeochemical cycle and are known to have a mutualistic interaction with different species of microalgae (Geng and Belas, 2010;González et al, 2000;Ramanan et al, 2016). This positive effect driven by the high bacterial biomass might also be due to the release of trace elements, such as a growth promoting factor, the hormone indole-3-acetic acid (de-Bashan et al, 2008), or by production of vitamins (Amin et al, 2012).…”

“…Complex relationships exist between these two organisms for both growth and carbon flux, bacteria can enhance EPS excretion by microalgae and/or fed on the excreted carbon (Amin et al, 2012;Ramanan et al 2016). Previous studies on the diatom T. weissflogii found variable results on transparent exopolymer particles (TEP) secretion related to the bacterial community associated to the algae (Crocker and Passow, 1995;Passow, 2002).…”