Hentschel, U. | Search bioRxiv

bioRxiv2018

The Neutral Metaorganism

Almost all animals and plants are inhabited by diverse communities of microorganisms, the microbiota. The hosts often pose highly selective environments, which only a subset of the environmentally available microbes are able to colonize. From the hosts perspective it seems useful to shape the community composition of these allowed microbes to promote a beneficial host-microbe symbiosis. In contrast to this, neutral models assume that the structure of the microbiota is entirely shaped by random population dynamics and dispersal. We here show that microbiota community structure from a wide range of host organisms, in particular including previously understudied invertebrates, is in almost all cases consistent with neutral expectations. Moreover, we demonstrate that apparent discrepancies with the neutral model can be due to transient community states rather than host selection. In conclusion, even though hosts are often assumed to control microbiota composition to ensure beneficial interactions, our broad-scale analysis highlights that following colonization, it could rather be neutral processes that determine microbial community structure.

ecology↗

bioRxiv2018

Marine sponges as Chloroflexi hot-spots: Genomic insights and high resolution visualization of an abundant and diverse symbiotic clade

Chloroflexi represent a widespread, yet enigmatic bacterial phylum. Meta-and single cell genomics were performed to shed light on the functional gene repertoire of Chloroflexi symbionts from the HMA sponge Aplysina aerophoba. Eighteen draft genomes were reconstructed and placed into phylogenetic context of which six were investigated in detail. Common genomic features of Chloroflexi sponge symbionts were related to central energy and carbon converting pathways, amino acid and fatty acid metabolism and respiration. Clade specific metabolic features included a massively expanded genomic repertoire for carbohydrate degradation in Anaerolineae and Caldilineae genomes, and amino acid utilization as nutrient source by SAR202. While Anaerolineae and Caldilineae import cofactors and vitamins, SAR202 genomes harbor genes encoding for co-factor biosynthesis. A number of features relevant to symbiosis were further identified, including CRISPRs-Cas systems, eukaryote-like repeat proteins and secondary metabolite gene clusters. Chloroflexi symbionts were visualized in the sponge extracellular matrix at ultrastructural resolution by FISH-CLEM method. Chloroflexi cells were generally rod-shaped and about 1 m in length, albeit displayed different and characteristic cellular morphotypes per each class. The extensive potential for carbohydrate degradation has been reported previously for Ca. Poribacteria and SAUL, typical symbionts of HMA sponges, and we propose here that HMA sponge symbionts collectively engage in degradation of dissolved organic matter, both labile and recalcitrant. Thus sponge microbes may not only provide nutrients to the sponge host, but also contribute to DOM re-cycling and primary productivity in reef ecosystems via a pathway termed the \"sponge loop\".

microbiology↗