Quorum Sensing Bacteria in the Phycosphere of HAB Microalgae and Their Ecological Functions Related to Cross-Kingdom Interactions.

Yanchao Zhang,Xiyuan Xu,Shuai Wang,Bin Han,Yangguo Zhao,Li Zheng,Tianyi Hu

doi:10.3390/ijerph19010163

Abstract

It has been proven that the relationship between microalgae and bacteria affects the dynamic process of harmful algal blooms (HABs). Microalgae-associated microorganisms widely exist in the phycosphere and play an essential role in algae-bacteria cross-kingdom interactions. Among these processes, quorum sensing (QS), as a communication system of bacteria, is thought to participate in algae-bacteria interactions. However, the species of QS bacteria in the phycosphere and their ecological function are still unknown. In this study, microalgae-associated microorganisms with a QS system were screened by the biosensor method and identified based on 16S rRNA gene analysis. The types and number of acyl-L-homoserine lactone (AHL) signalling molecules produced by QS bacteria were analysed by thin layer chromatography (TLC) bioautography and gas chromatography-mass spectrometer (GC-MS). The film formation, β-dimethylmercaptopropionic (DMSP) degradation and algae growth effects of QS bacteria were investigated. The results showed that 113 QS bacteria were isolated from 842 microalgae-associated bacteria. Detection of AHL molecules in 10 different species of QS bacteria showed that most of them were N-(3-Oxodecanoyl)-L-homoserine lactone (OC10-HSL), N-Octanoyl-L-homoserine lactone (C8-HSL) and N-(3-Oxooctanoyl)-L-homoserine lactone (OC8-HSL). All 10 QS bacteria had film-forming ability, and they could degrade DMSP (except strain E26). The crude metabolic extracts of the 10 QS bacteria can inhibit or promote microalgae growth to different degrees. Our study is helpful to understand the role of microalgae-associated microorganisms with the QS system in algae-bacteria interactions and community succession of HAB microalgae.

Highlights

Introduction iationsDuring the process of growth, microalgae release dissolved organic matter (DOM)and particulate organic matter (POM) into the environment
The results showed that the 10 quorum sensing (QS) strains belonged to four genera, Sulfitobacter, Ponticoccus, Leisingera and Nitratireductor, which all fall in the class of α-Proteobacteria
The results showed that the bacteria proTLC-bioautography and gas chromatography-mass spectrometer (GC-MS) were used to analyse the profile of QS

Summary

Introduction

During the process of growth, microalgae release dissolved organic matter (DOM). Particulate organic matter (POM) into the environment. A unique microenvironment is formed around algal cells called the phycosphere [1,2]. Previous studies found that the bacteria in the phycosphere proliferated by utilizing organic material released by microalgae [5]. Others secrete algicidal substances that inhibit the growth of microalgae or lead to the aggregation and deposition of microalgae [9,10]. This process is thought to be a mechanism used to control the numbers and populations of microalgae to maintain the ecological balance of the phycosphere [5]

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