Shedding light on the function of marine sponge microbiota

Sponges are the most ancient metazoan animal phylum (approximately 600 million years old) and are found in tropical and subtropical oceans, the polar regions, the deep sea and in freshwater lakes and streams. Marine demosponges harbour complex microbial communities at densities exceeding the surrounding seawater by several orders of magnitude and sometimes these microorganisms make up 40-60% of the animals biomass. While the majority of the microorganisms remain unculturable, Grozdanov & Hentschel (2007) review several of the discoveries made using environmental genomic techniques shedding light on the function of sponge-associated microbiota.

The archaeon Cenarchaeum symbiosum (C. archaeum lineage) has now been found in more than 19 shallow water sponge species, and in an arctic deep water sponge, making up 70-90% of the microbial biomass. Interestingly, it is thought that the C. archaeum lineage consistently affiliated with the sponges is not thermophillic; sequence comparison of several clones carrying the ribosomal operon and subsequent biochemical characterization of the enzyme revealed enzyme instability above 40^oC. Also, the presence of molecular machinery encoding a modified version of the 3-hydroxypropionate cycle for CO₂ assimilation and the identification of genes using reduced nitrogen compounds and ammonia for energy production might be evidence for a symbiotic relationship between the sponge host and the archaeon, in which removal of sponge waste products such as ammonia would provide energy for the symbiont while CO₂ fixation by the archaea would supply organic carbon to the sponge. A complete genome of C. symbiosum was generated by systematical selection of overlapping clones from environmental fosmid libraries and this has shown that many predicted genes appear to be specific and Grozdanov & Hentschel (2007) suggest that these may perform symbiosis-related functions such as mediation of cell-to-cell contact, degradation of extracellular matrix proteins or evasion of the host defences.

Several of the studies reviewed give evidence for a bacterial origin of onnamides, a group of polyketide compounds that exhibit powerful anti-tumour activities. The onnamides gene cluster follows the co-linearity rule in that the domain architecture of the involved genes mirrors the chemical structure of the onnamides nearly perfectly. Research on the diversity of PKSI genes led to the discovery of unusually small monomodular and widely distributed PKSI operons in sponge microbiota that are similar to methyl-branched fatty-acid-encoding PKS systems from Mycobacteria. The biological function of these in sponges is unclear but Grozdanov & Hentschel thought that these methylated fatty acids may be important for the establishment and maintenance of symbiosis by protecting the bacterial cells from phagocytosis. Several other compounds that are known to be secondary metabolites found in sponges as well as biotechnologically relevant compounds have been found to be produced by the sponge microbiota also.

This was an interesting paper highlighting some of the main findings surrounding marine sponges and the potential applications for some of the compounds produced by their microbial communities. These are of interest both medically and for biotechnology. Much of the information given for each point was from several separate studies and references for each can be found within the Grozdanov & Hentschel (2007) paper.

 

Grozdanov, L. & Hentschel, U. (2007) An environmental genomics perspective on the diversity and function of marine sponge-associated microbiota. Ecology and industrial microbiology. 10, 215-220