The Influence of Bacteria on Animal Metamorphosis

Abstract

The swimming larvae of many marine animals identify a location on the seafloor to settle and undergo metamorphosis based on the presence of specific surface-bound bacteria. While bacteria-stimulated metamorphosis underpins processes such as the fouling of ship hulls, animal development in aquaculture, and the recruitment of new animals to coral reef ecosystems, little is known about the mechanisms governing this microbe-animal interaction. Here we review what is known and what we hope to learn about how bacteria and the factors they produce stimulate animal metamorphosis. With a few emerging model systems, including the tubeworm Hydroides elegans, corals, and the hydrozoan Hydractinia, we have begun to identify bacterial cues that stimulate animal metamorphosis and test hypotheses addressing their mechanisms of action. By understanding the mechanisms by which bacteria promote animal metamorphosis, we begin to illustrate how, and explore why, the developmental decision of metamorphosis relies on cues from environmental bacteria.

Two distinct bacterial biofilm components trigger metamorphosis in the colonial hydrozoanHydractinia echinata

“…The resulting active HPLC fractions were analyzed by high-resolution tandem mass spectrometry (HR-MS 2 ) and Global Natural Product Social Molecular Networking (GNPS) 28 analysis, which revealed the dominant presence of phosphatidylglycerols (PGs) and phosphatidylethanolamines (PEs) and the respective lyso derivatives (LPGs, LPEs) (Figure S11-S13). Due to inherent difficulties associated with the purification of structurally closely related phospholipids, commercial derivatives with matching LC-HRMS 2 pattern (Figure S40-S50) and 1 H and 13 C nuclear magnetic resonance (NMR) spectra (Figure S26-S39) as well as two fluorescence-labeled derivatives were tested in a standardized assay (Figure 5, Figure S14-S15, Table S3). Two lysophospholipids (16:0 LPG, 16:0 LPA), phosphatidylethanolamine 18:0 PE, and 1,2-dipalmitoyl-sn-glycero-3-phosphate (16:0 PA) repeatedly induced settlement and metamorphosis in 20-40% of all larvae within 48 h, while phospholipid concentrations exceeding 50 µM occasionally caused lysis of larvae (Figure 5).…”

“…We then focused on the analysis of the most active HMW fractions (up to 80-100% metamorphosis) retrieved from aqueous extracts of bacterial biomass (Figure 2). First, the HMW fraction was purified using size-exclusion filtration (Figure S9) and fractions causing more than 20% of all larvae to metamorphose were analyzed by 1 H NMR. Comparative analysis indicated towards a complex mixture of yet unknown polysaccharides (Figure S21) and further bioassay-guided purification using Sephadex G25 was performed.…”

“…Supplementary Information (SI) is available at https://zenodo.org with the DOI:10.5281/zenodo.4537693. SI material contains details on fermentation, cultivation, sample treatment, bioassays, isolation procedures, ESI-HRMS, 1 H NMR, 13 C NMR, and 2D NMR spectra as well as additional assay data.…”

“…Measurement were performed on a Thermo Q-Exactive Plus using the following gradient: 0–1 min, 20% B; 1–2 min, 20%–40% B; 2–25 min, 40%–92.5% B; 25–26 min, 92.5%–100% B; 26–35 min, 100% B; 35–35.1 min, 100%–20% B; 35.1–38 min, 20% B (A: dd H 2 O with 20 mM ammonium formate pH 4.5; B: 50% i PrOH/50% MeCN), flow rate: 0.3 mL/min. Metabolite separation was followed by a data-dependent MS/MS analysis in both positive (MS 1 ) and negative (MS 1 and MS 2 ) ionization modes.…”

“…The radical transformation (metamorphosis) of motile larvae into the adult stage is a critical step in the life cycle of many marine species as it confers the propagation and persistence of the population in the marine ecosystem. 1 For more than 80 years it has been recognized that chemical signals present within marine biofilms induce the settlement and metamorphosis in larvae, 2,3,4 but the identification of these signaling molecules remains still a challenging task and until today and only very few key bacterial signals have been structurally characterized and functionally analyzed. 5,6,7 One of the few identified bacterial signaling molecules are bromopyrroles produced by Pseudoalteromonas that induce metamorphosis in coral larvae, 8,9 but larvae failed to attach to surfaces when stimulated by bromopyrroles alone and it was deduced that other, yet unidentified, chemical cues are important for the morphogenic process.…”