Abstract
BackgroundMarine sponges can associate with abundant and diverse consortia of microbial symbionts. However, associated bacteria remain unexamined for the majority of host sponges and few studies use phylogenetic metrics to quantify symbiont community diversity. DNA fingerprinting techniques, such as terminal restriction fragment length polymorphisms (T-RFLP), might provide rapid profiling of these communities, but have not been explicitly compared to traditional methods.Methodology/Principal FindingsWe investigated the bacterial communities associated with the marine sponges Hymeniacidon heliophila and Haliclona tubifera, a sympatric tunicate, Didemnum sp., and ambient seawater from the northern Gulf of Mexico by combining replicated clone libraries with T-RFLP analyses of 16S rRNA gene sequences. Clone libraries revealed that bacterial communities associated with the two sponges exhibited lower species richness and lower species diversity than seawater and tunicate assemblages, with differences in species composition among all four source groups. T-RFLP profiles clustered microbial communities by source; individual T-RFs were matched to the majority (80.6%) of clone library sequences, indicating that T-RFLP analysis can be used to rapidly profile these communities. Phylogenetic metrics of community diversity indicated that the two sponge-associated bacterial communities include dominant and host-specific bacterial lineages that are distinct from bacteria recovered from seawater, tunicates, and unrelated sponge hosts. In addition, a large proportion of the symbionts associated with H. heliophila were shared with distant, conspecific host populations in the southwestern Atlantic (Brazil).Conclusions/SignificanceThe low diversity and species-specific nature of bacterial communities associated with H. heliophila and H. tubifera represent a distinctly different pattern from other, reportedly universal, sponge-associated bacterial communities. Our replicated sampling strategy, which included samples that reflect the ambient environment, allowed us to differentiate resident symbionts from potentially transient or prey bacteria. Pairing replicated clone library construction with rapid community profiling via T-RFLP analyses will greatly facilitate future studies of sponge-microbe symbioses.
Highlights
Sponge-microbe symbioses represent novel associations between an ecologically successful phylum of basal invertebrates and genetically diverse consortia of distinct microbial lineages [1,2,3]
We investigated the bacterial community associated with H. heliophila from the northern Gulf of Mexico, along with the communities associated with a sympatric sponge, Haliclona tubifera, a sympatric tunicate, Didemnum sp., and the ambient seawater
Diversity and composition of microbial communities A total of 389 bacterial sequences were recovered from sponge, tunicate, and seawater samples, representing 159 unique bacterial operational taxonomic units (OTUs), according to an OTU definition of 99% similarity (Figure 1, Figure 2, Figure 3, Figure S1)
Summary
Sponge-microbe symbioses represent novel associations between an ecologically successful phylum of basal invertebrates and genetically diverse consortia of distinct microbial lineages [1,2,3]. Symbiotic bacterial communities often exhibit high abundance within the sponge host, comprising up to 35% of total holobiont biomass [4], while the biodiversity of sponge-associated microorganisms includes representatives from most major clades of Bacteria [5,6] and Archaea [7,8,9]. The broad implications of sponge-bacterial symbioses have prompted a recent surge in the field of sponge microbiology [1,2,3], but many fundamental questions remain unresolved. It is often unclear whether these symbionts are generalists that associate with all sponges at a particular location, or specialists that associate with a single host species. DNA fingerprinting techniques, such as terminal restriction fragment length polymorphisms (T-RFLP), might provide rapid profiling of these communities, but have not been explicitly compared to traditional methods
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