Masaaki Morikawa

Duckweed-associated plant growth-promoting bacteria have attracted attention for their potential to enhance duckweed biomass production. However, the mechanisms underlying isolate-specific growth promotion are unclear. This study compared the effects of two duckweed-associated bacterial isolates, Terrimicrobium sp. PS02 and Aeromicrobium sp. PS05, on the growth, biomass composition, colonization behavior, and transcriptomic responses of Spirodela polyrhiza. Biomass composition and transcriptome analyses were performed to characterize the host responses. Both isolates enhanced duckweed biomass; PS02 increased it 1.2-fold, whereas PS05 induced a significant 1.4-fold increase compared to the uninoculated control. PS05 established bacterial populations approximately one order of magnitude higher than those of PS02 and formed dense extracellular polymeric substance-mediated microcolonies on the surface. Transcriptome analysis revealed that PS05 induced 1108 differentially expressed genes, compared with 454 in PS02, indicating greater host transcriptomic reprogramming. Functional enrichment of transcriptome responses showed that PS05 preferentially regulates carbohydrate biosynthesis, central carbon metabolism, and starch biosynthesis, significantly enhancing starch accumulation and turion formation without reducing protein or photosynthetic pigment content. This study provides evidence linking bacterial colonization, host transcriptomic regulation, carbon allocation, and biomass production in duckweed, offering a basis for engineering high-performance duckweed–microbiome systems for sustainable biomass production.

Wolffia (Lemnoideae) is recognised as a nutritional superfood with increasing interest in commercial cultivation. Its growth and biomass quality are influenced by abiotic factors and duckweed‐associated bacteria (DAB) that support nutrient cycling, stress tolerance and metabolism. This study assessed DAB diversity and their effects on Wolffia growth to select effective plant growth‐promoting bacteria (PGPB) and elucidated beneficial plant‐microbe interactions. A total of 108 isolates, representing 66 species from 41 genera across four phyla, were obtained from duckweeds collected in six provinces of Thailand. The culturable DAB community showed high taxonomic diversity, dominated by the phylum Pseudomonadota, particularly Alphaproteobacteria. The isolates, along with the known PGPB of Spirodela polyrhiza , were evaluated for growth promotion in axenic Wolffia globosa using co‐cultivation. Six PGPB enhanced growth by 54.67%–77.75% without reported pathogenicity. Several PGPB originally isolated from S. polyrhiza also showed growth‐promoting effects on Wolffia . Large‐scale co‐cultivation demonstrated that Pseudomonas toyotomiensis W5–11 most effectively increased dry weight and chlorophyll content (3.18‐ and 2.75‐fold, respectively). All selected isolates produced indole‐3‐acetic acid (IAA), siderophores and solubilised phosphate. Correlation analysis revealed that IAA production was associated with protein accumulation. These findings suggested that PGPB represent promising biofertilisers that enhance Wolffia productivity and nutritional quality through various mechanisms.

Alkylresorcinols (AR) are a class of phenolic lipids widely distributed in plants, algae, fungi, and bacteria. AR are high-value bioproducts with applications in a broad range of industries, ranging from agriculture to healthcare. They are, however, hydrophobic and found in trace amounts, especially in hard grain bran, and thus require intensive mechanical crushing and harmful organic solvent-based processes for elution. The aim of this study is to demonstrate a proof-of-concept of an innovative AR production and extraction technology to ensure hygienic and safe working environments. In this study, we examined the competency of AR production by diazotrophic bacteria Azotobacter vinelandii using various surfactants. The effect of selected surfactant was tested not only at the stage of AR elution from cysts but also during the cell culture forming cysts. It revealed that nonionic surfactants, Tween-20 and Tween-80, were capable of not only solubilizing AR from the mature cysts of A. vinelandii but also increasing their production during cyst formation. The production yield of AR in soluble form maximally reached 5.5 mg/L in Burk’s nitrogen-free liquid medium containing 0.2% n-butanol and 0.1% Tween-20. These findings contribute to the development of an efficient and solvent-free green production method for AR.

Duckweed is a rapidly-growing aquatic plant utilized as food/feed and for wastewater remediation. It coexists with complex microbial communities that play crucial roles in its growth and capability for phytoremediation. In a previous study, microbiomes associated with four duckweed species ( Spirodela polyrhiza , Landoltia punctata , Lemna aequinoctialis , and Wolffia globosa ) grown under natural and nutrient-deficient conditions, were investigated using V3V4 16S rRNA sequencing. However, species-level classification was not achieved due to the partial 16S rRNA sequences obtained, restricting the selection of potential microbial species for further application. In this study, L. punctata samples from the previous work were investigated further by employing full-length 16S rRNA sequencing. A total of 31 predominant microbial species were identified. Under stress, the proportion of Proteobacteria increased significantly, along with potentially beneficial bacteria such as Roseateles depolymerans , Pelomonas saccharophila , Acidovorax temperans , Ensifer adhaerens and Rhizobium straminoryzae . Functional metagenomic predictions suggest that associated microbes adapt to stressors and may confer benefits to duckweed, including pathways related to host adhesion, biofilm formation, microbial growth modulation, and co-factors and vitamin biosynthesis. Furthermore, the study demonstrates both the advantages and limitations of full-length 16S rRNA amplicon sequencing. The findings provide more insight into L. punctata microbiomes at species-level, facilitating establishment of stable, beneficial microbial communities for duckweed applications. Ongoing investigations aim to isolate key microbial species from L. punctata and validate their roles through co-cultivation, along with establishing potential synthetic microbial communities based on the metagenomic findings.

Black soldier fly larvae (BSFL) and duckweed are potential alternative feed ingredients for sustainable poultry production. This study aimed to determine the standardized ileal digestibility (SID) of amino acids (AAs) in BSFL, Lemna, and Spirodela compared with soybean meal and rapeseed meal. Six cages of eighteen broiler chickens were allocated to each treatment. The crude protein (CP) content was highest in soybean meal (511 g/kg dry matter; DM), intermediate in BSFL (391 g/kg), and rapeseed meal (335 g/kg DM) and lowest in Lemna (185 g/kg DM) and Spirodela (145 g/kg DM). Ether extract was highest in BSFL (95 g/kg DM), whereas crude fiber was highest in Lemna (109 g/kg DM) and Spirodela (171 g/kg DM). The SID of CP was higher (p < 0.05) in BSFL (89.0%) than in soybean meal (82.3%), rapeseed meal (71.3%), Lemna (70.2%), and Spirodela (44.9%). The SID of all essential amino acids (AAs) was higher (p < 0.05) in Lemna than in Spirodela, but it did not differ from that in rapeseed meal. In conclusion, the high fat content in BSFL can enhance AA digestibility, whereas the use of duckweed may be limited by its fiber fractions, which negatively impact the SID of CP and AAs in broiler chickens.

We report the complete genome sequence of strain MRC-7, which represents a potentially novel genus within the family Opitutaceae. The genome was 4,342,534 bp in size and contained 3,428 protein-coding sequences, several of which were predicted to be involved in pectin degradation.

Understanding the processes through which plant‐associated microbiomes influence host physiology and fitness is a central goal of plant–microbiome interaction research. While traditional model plants such as Arabidopsis thaliana have provided foundational platforms to examine these processes, alternative model systems may address certain bottlenecks in current research. In recent years, duckweeds (family Lemnacea) have emerged as a unique model plant offering several experimental advantages owing to their small size, simple morphology, aquatic habitat, and two‐dimensional clonal growth. These features facilitate the establishment of highly tractable and reproducible model systems that facilitate robust investigations and high‐throughput screening platforms, enabling multifactorial massive parallel experiments. This review provides an overview of the recent studies that have applied the advantages of using duckweed in the field of plant–microbiome interactions to highlight how duckweed‐based systems have enabled unique experimental approaches that are difficult in conventional systems. We have also discussed the emerging directions in duckweed–microbiome research, including elucidation of the co‐evolutionary processes mediated via metabolic exchange and bottom‐up explanation of community structure and functions using synthetic bacterial communities. Together, this review underscores the potential of duckweed to serve as a distinctive model for advancing plant–microbiome interaction research.