Effects of <i>Acanthamoeba</i> spp. on rice ( <i>Oryza sativa</i> L.) plant growth and rhizobacterial community composition

AIMS: This study aimed to evaluate the influence of two amoebae (Acanthamoeba lenticulata (A10) and Acanthamoeba genotype T4 (A23)) on rice growth, nutrient uptake, and rhizobacterial community composition. METHODS AND RESULTS: Rice seedlings were inoculated with either A10 or A23 and grown under greenhouse conditions for 30 d. Plant growth parameters, biomass accumulation, and nutrient contents were determined. Rhizosphere bacterial community diversity and composition were assessed using 16S rRNA gene amplicon sequencing followed by statistical analyses including Tukey's HSD test (p < 0.05). Both amoebae significantly increased root length (33-36%) compared to uninoculated controls. A10 exerted stronger effects on biomass accumulation, increasing the root fresh weight (136%), shoot fresh weight (94%), root dry weight (325%), and shoot dry weight (188%). Both treatments enhanced nutrient uptake, particularly phosphorus content. Although the bacterial alpha diversity indices did not differ significantly among the treatments; clear shifts in community composition were observed. Amoebae-inoculated soils were enriched in Proteobacteria (65-75%), whereas Firmicutes dominated the control soils (34%). Several plant beneficial genera such as Methylobacillus, Methylotenera, Methylobacterium, Sphingomonas, Acinetobacter, and Novosphingobium were more abundant in amoebae-treated rhizospheres. CONCLUSIONS: Acanthamoeba species enhanced rice growth and nutrient acquisition by selective restructuring of rhizosphere bacterial communities.