Metabolically-versatileCa.Thiodiazotropha symbionts of the deep-sea lucinid clamLucinoma kazanihave the genetic potential to fix nitrogen

Abstract

AbstractLucinid clams are one of the most diverse and widespread symbiont-bearing animal groups in both shallow and deep-sea chemosynthetic habitats. Lucicnids harborCa. Thiodiazotropha symbionts that can oxidize inorganic and organic substrates such as hydrogen sulfide and formate to gain energy. The interplay between these key metabolic functions, nutrient uptake and biotic interactions inCa. Thiodiazotropha is not fully understood. We collectedLucinoma kazaniindividuals from next to a deep-sea brine pool in the eastern Mediterranean Sea, at a depth of 1150 m and used Oxford Nanopore and Illumina sequencing to obtain high-quality genomes of theirCa.Thiodiazotropha gloverae symbiont. The genomes served as the basis for transcriptomic and proteomic analyses to characterize thein situgene expression, metabolism and physiology of the symbionts. We found genes needed for N2fixation in the deep-sea symbiont’s genome, which, to date, were only found in shallow-waterCa. Thiodiazotropha. However, we did not detect the expression of these genes and thus the potential role of nitrogen fixation in this symbiosis remains to be determined. We also found the high expression of carbon fixation and sulfur oxidation genes, which indicates chemolithoautotrophy as the key physiology ofCa. Thiodiazotropha. However, we also detected the expression of pathways for using methanol and formate as energy sources. Our findings highlight the key traits these microbes maintain to support the nutrition of their hosts and interact with them.