Decay experiments and microbial community analysis of water lily leaf biofilms: Sediment effects on leaf preservation potential

by Brianne Palmer, Sabina Karačić, Shook Ling Low, Kathrin Janssen, Harald Färber, Moritz Liesegang, Gabriele Bierbaum, Carole T. Gee

Understanding the intricate dynamics of sediment-mediated microbial interactions and their impact on plant tissue preservation is crucial for unraveling the complexities of leaf decay and preservation processes. To elucidate the earliest stages of leaf preservation, a series of decay experiments was carried out for three months on Nymphaea water lily leaves in aquariums with pond water and one of three distinctly different, sterilized, fine-grained substrates—commercially purchased kaolinite clay or fine sand, or natural pond mud. One aquarium contained only pond water as a control. We use 16S and ITS rRNA gene amplicon sequencing to identify and characterize the complex composition of the bacterial and fungal communities on leaves. Our results reveal that the pond mud substrate produces a unique community composition in the biofilms compared to other substrates. The mud substrate significantly influences microbial communities, as shown by the correlation between high concentrations of minerals in the water and bacterial abundance. Furthermore, more biofilm formers are observed on the leaves exposed to mud after two months, contrasting with declines on other substrates. The mud substrate also enhanced leaf tissue preservation compared to the other sediment types, providing insight into the role of sediment and biofilms in fossilization processes. Notably, leaves on kaolinite clay have the fewest biofilm formers by the end of the experiment. We also identify key biofilm-forming microbes associated with each substrate. The organic-rich mud substrate emerges as a hotspot for biofilm formers, showing that it promotes biofilm formation on leaves and may increase the preservation potential of leaves better than other substrates. The mud’s chemical composition, rich in minerals such as silica, iron, aluminum, and phosphate, may slow or suspend decay and facilitate biomineralization, thus paving the way toward leaf preservation. Our study bridges the information gap between biofilms observed on modern leaves and the mineral encrustation on fossil leaves by analyzing the microbial response in biofilms to substrate types in which fossil leaves are commonly found.