Bacterial response to spatial gradients of algal-derived nutrients in a porous microplate

Abstract

Photosynthetic microalgae are responsible for 50% of the global atmospheric CO2 fixation into organic matter and hold potential as a renewable bioenergy source. Their metabolic interactions with the surrounding microbial community (the algal microbiome) play critical roles in carbon cycling, but due to methodological limitations, it has been challenging to examine how community is developed by spatial proximity to their algal host. Here we introduce a hydrogel-based porous microplate to co-culture algae and bacteria, where metabolites are constantly exchanged between the microorganisms while maintaining physical separation. In the microplate we found that the diatom Phaeodactylum tricornutum accumulated to cell abundances ~20 fold higher than under normal batch conditions due to constant replenishment of nutrients through the hydrogel. We also demonstrate that algal-associated bacteria, both single isolates and complex communities, responded to inorganic nutrients away from their host as well as organic nutrients originating from the algae in a spatially predictable manner. These experimental findings coupled with a mathematical model suggest that host proximity and algal culture growth phase impact bacterial community development in a taxon-specific manner through organic and inorganic nutrient availability. Our novel system presents a useful tool to investigate universal metabolic interactions between microbes in aquatic ecosystems.

Characterizing chemical signaling between engineered “microbial sentinels” in porous microplates

“…In this manuscript, we describe a “porous microplate” consisting of spatially isolated culture wells separated by porous methacrylate barriers (Ge et al , 2016; Kim et al , 2021). The methacrylate we choose, hydroxyethyl methacrylate‐ co ‐ethylene glycol dimethacrylate (HEMA‐EDMA), has amorphous pores of 10–100 nm in size and a porosity of 60 percent.…”

Dynamic Phaeodactylum tricornutum Exometabolites Shape Surrounding Bacterial Communities

“…A previous study using porous microplates with gradients of inorganic nutrients and algal DOC found that growth of Marinobacter (same isolate used here) was dependent on access to inorganic nutrients along with algal DOC (34). However, that study also found that when a bacterial enrichment community (one of the same enrichments used here) was grown in adjacent porous microplate wells to P. tricornutum, its response was similar to this study's spent medium response (increases in Marinobacter, Oceanicaulus and Algoriphagus, and a decrease in Alcanivorax relative abundance), not the algal presence response (40).This suggests that direct physical interaction is required for the inhibition effect observed in this study (34). Other work has shown that antimicrobial fatty acids from P. tricornutum cell pellets selectively inhibited some bacterial taxa (42), suggesting one potential mechanism of selective controls of bacterial growth tied to algal presence.…”

“…Competition for inorganic nutrients may contribute to this effect. A previous study using porous microplates with gradients of inorganic nutrients and algal DOC found that growth of Marinobacter (same isolate used here) was dependent on access to inorganic nutrients along with algal DOC (34). However, that study also found that when a bacterial enrichment community (one of the same enrichments used here) was grown in adjacent porous microplate wells to P. tricornutum , its response was similar to this study’s spent medium response (increases in Marinobacter , Oceanicaulus and Algoriphagus , and a decrease in Alcanivorax relative abundance), not the algal presence response (40).…”

“…Thus, the composition of algal exometabolites experienced by bacteria growing with algae likely differs from that of the spent medium from axenic algae. Previous work in our lab investigated bacterial responses to P. tricornutum exudates using a porous microplate to physically separate algae and bacteria but allow metabolite exchange (34). Using one of the same bacterial enrichment cultures used here, that study identified four bacterial genera ( Marinobacter , Oceanicaulis , Algoriphagus , and Muricauda ) that responded positively to P. tricornutum metabolites diffusing through the hydrogel.…”

“…Previous work in our lab investigated bacterial responses to P. tricornutum exudates using a porous microplate to physically separate algae and bacteria but allow metabolite exchange (34).…”