Diverse interactions between bacteria and microalgae: A review for enhancing harmful algal bloom mitigation and biomass processing efficiency

Abstract

The interactions between bacteria and microalgae play pivotal roles in resource allocation, biomass accumulation, nutrient recycling, and species succession in aquatic systems, offering ample opportunities to solve several social problems. The escalating threat of harmful algal blooms (HABs) in the aquatic environment and the lack of cheap and eco-friendly algal-biomass processing methods have been among the main problems, demanding efficient and sustainable solutions. In light of this, the application of algicidal bacteria to control HABs and enhance algal biomass processing has been promoted in the past few decades as potentially suitable mechanisms to solve those problems. Hence, this comprehensive review aims to explore the diverse interaction modes between bacteria and microalgae, ranging from synergistic to antagonistic, and presents up-to-date information and in-depth analysis of their potential biotechnological applications, particularly in controlling HABs and enhancing microalgal biomass processing. For instance, several studies revealed that algicidal bacteria can effectively inhibit the growth of Microcystis aeruginosa, a notorious freshwater HAB species, with an antialgal efficiency of 24.87 %-98.8 %. The review begins with an overview of the mechanisms behind algae-bacteria interactions, including the environmental factors influencing these dynamics and their broader implications for aquatic ecosystems. It then provides a detailed analysis of the role of algicidal bacteria in controlling harmful algal blooms, as well as their role in bioflocculation and the pretreatment of microalgal biomass. Additionally, the review identifies and discusses the constraints and challenges in the biotechnological application of these interactions. By exploring the strategic use of algicidal bacteria, this review not only underscores their importance in maintaining aquatic environmental health but also in enhancing biomass processing efficiency. It offers valuable insights into future research avenues and the potential scalability of these applications, both in situ and at an industrial level.

Keywords: Algicidal bacteria; Biological pretreatment; Cell wall; Environmental factors; Flocculation; Harmful algal blooms; Interaction.

Graphical abstract

Fig. 1

A diagram illustrating different forms of bacteria and microalgae interaction in an open aquatic environment in a) free-living interaction b) phycospheric interaction with the diffusive boundary created between the outside periphery and phycosphere, where the microalga exuded dissolved organic carbon (DOC), while both partners exchange nutrients (nitrogen-N, phosphorus-P, and carbon dioxide-CO₂) with gradient of concentration from the inner part to the periphery, and c) cell-to-cell contact interaction involved in entanglement with bacterial flagella.

Fig. 2

A diagram illustrating the free exchange of resources, the negative and the positive interactions between microalgae and bacteria facilitated through the free exchange of nutrients or signal molecules and quorum sensing. Where, the dissolved organic matter (DOM), the cell degrading product (CDP), tryptophan and thamin originated from the microalgae and then assimilated and act on bacteria, while indole acetic acid (IAA), vitamins, siderophores, acetate, lytic enzymes originated from bacteria then acted on microalgae, and the quorum sensing can be applied within bacteria or between bacteria and microalgae facilitating the interactions. The illustration depicted is based on [27,60].

Fig. 3

An illustration depicting a) the direct and indirect attack with an exemplary predatory lifestyle of Vampirovibrio chlorellavorus where sections indicating the bacterium locating the prey-the bacterium seeks out the host (C. vulgaris) cells via chemotaxis and flagella (i), attachment and formation of secretion apparatus (ii), ingestion-hydrolytic enzymes are transferred to the prey cells where they degrade algal cell contents (iii), binary division-algal cell exudates are ingested by V. chlorellavorus allowing it to replicate by binary division, and releasing of progeny (iv), the illustration depicted based on Soo et al. [172], b) the direct and indirect attack of bacteria on microalgae, and c) indirect attack of bacteria by secretion of hydrolytic enzymes.

Fig. 4

A diagram illustrating a) the stable suspension of microalgae in the media due to the repulsion force created by the negatively charged surface of microalgae, and b) the flocculation of the microalgae biomass due to the bioflocculation effect of a bacterial exocellular polymeric substance (EPS).

Fig. 5

A schematic diagram showing the general processes involved in the utilization of algicidal bacteria in controlling HAB. Detailed information is indicated in Coyne et al. [28].