Kynurenic acid mediates bacteria-algae consortium in resisting environmental cadmium toxicity

Genetic evidence for algal auxin production in Chlamydomonas and its role in algal-bacterial mutualism

Interactions between algae and bacteria are ubiquitous and play fundamental roles in nutrient cycling and biomass production. Recent studies have shown that the plant auxin indole acetic acid (IAA) can mediate chemical crosstalk between algae and bacteria, resembling its role in plant-bacterial associations. Here, we report a mechanism for algal extracellular IAA production from L-tryptophan mediated by the enzyme L-amino acid oxidase (LAO1) in the model Chlamydomonas reinhardtii. High levels of IAA inhibit algal cell multiplication and chlorophyll degradation, and these inhibitory effects can be relieved by the presence of the plant-growth-promoting bacterium (PGPB) Methylobacterium aquaticum, whose growth is mutualistically enhanced by the presence of the alga. These findings reveal a complex interplay of microbial auxin production and degradation by algal-bacterial consortia and draws attention to potential ecophysiological roles of terrestrial microalgae and PGPB in association with land plants.

Carbon sequestration performance, enzyme and photosynthetic activity, and transcriptome analysis of algae-bacteria symbiotic system after antibiotic exposure

Wastewater treatment technology based on algae-bacteria successfully combines pollutant purification, CO2 reduction and clean energy production to provide new insights into climate solutions. In this study, the reciprocal mechanisms between algae and bacteria were explored through physiological and biochemical levels of algae cells and differentially expressed genes (DEGs) based on the performance of immobilized algae-bacteria symbiotic particles (ABSPs) for CO2 fixation. The results showed that ABSPs promoted the CO2 fixation capacity of microalgae. The enhanced growth capacity and photosynthetic activity of algal cells in ABSPs are key to promoting CO2 uptake, and the stimulation of photosynthetic system and the promotion of Calvin cycle were the main contributors to enhanced carbon sequestration. These findings will provide guidance for carbon reduction using immobilized ABSS as well as deciphering the algae-bacteria reciprocal mechanism.

Influence of phycospheric bacterioplankton disruption or removal on algae growth and survival

Phycospheric bacteria play a crucial role in the survival of microalgae. However, the potential of using the growth regulation and community structure modulation of phycospheric bacteria to prevent the occurrence of blooms is yet to be verified. The phycospheric bacterioplankton of Cyclotella sp. can be categorized into HNA (high nucleic acid) bacteria and LNA (low nucleic acid) bacteria. 16S rRNA sequencing showed that the HNA bacteria exhibited higher α-diversity compared to the LNA bacteria, and the microbial community composition also exhibited variations. Metagenomic sequencing further indicated the distinct ecological functions between HNA and LNA bacteria. Furthermore, the study showcased the restorative capacity of the phycospheric bacterioplankton. Biomass analysis revealed that the recovery of phycospheric bacterioplankton positively influenced the microalgae growth, thus affirming the significance of phycospheric bacterioplankton to microalgae. The community structure of phycospheric bacterioplankton demonstrated a notable decrease in the abundance of restored LNA core bacteria. Additionally, the restored phycospheric bacterioplankton exhibited a more complex co-occurrence network structure, resulting in decreased resistance and sensitivity of microalgae to adverse environments. The presence of phycospheric bacterioplankton provides a protective shield for microalgae, and thus destabilizing or removing phycospheric bacterioplankton may effectively inhibit growth of microalgae.