Nutrient Cycling Microbes within a Deep Sea Sponge

Ammonia Oxidising Archaea (AOA), Nitrite-oxidising Bacteria (NOB) and Sulfur-oxidising Bacteria (SOB) have all been found to be largely important in the widespread respective cycles within the marine environment. Previous research has looked at corals and their microbial associations, but very little work has discovered if sponges have microbial assemblages and if any of these associations involve nutrient cycle associated prokaryotic organisms. This is especially true in the deep sea glass sponges; this is until Tian et al (2016) studied Lophophysema eversa and its acquaintances.

Lophophysema eversa samples were collected from the South China Sea and sponge tissue was dissected to obtain the microbial associates. The authors do not state if any precautions were taken to ensure the microbial sequences were actually from the sponge or just from the surrounding seawater.

They found three dominant species that accounted for 95% of the microbial community Nitrosopumilus (AOA), unidentified Nitrospina (NOB) and an unidentified Gammaproteobacteria (potentially a SOB). The Gammaproteobacteria discovered shared 90% identity with an organism that can oxidise sulfur, Thioalkalivibrio sulfidophilus HL-EbGR7. Maybe this unidentified potential SOB can indeed oxidise sulfur, but I began to question whether this is a tenuous link to tell a nicely fitted story. Until considerably later, on when they backed up their claim, demonstrated by the presence of several enzymes to reduce various sulfur containing compounds.

The gene identity of the AOA was 97.7% similar to a marine free living AOA. This evoked the question, is it actually associated with the sponge in this study at all or is has it just arisen from poor sampling? The NOB discovered has genes for encoding subunits of nitrate oxidoreductase, an enzyme necessary for an NOB to perform the second step of nitification. Unlike free living NOBs there were genes for protection against foreign DNA (restriction modification system). It also has a complete pathway for the production of Vitamin B12, a feature of other microbial associates in sponges. The authors fail to mention why the presence of B12 and restriction modification systems would be of significance.

Both AOA and NOBs have more genes for chemotaxis than the most closely related free living counterparts. The authors proposed that this may be for movement to more favourable environments within the sponge (as they have been shown to have microenvironments within the sponge). Although, they provided no information on the mobility genes to back up this assumption; this would make a nice area for further research.

I feel the paper is written in a structure that is hard to follow as a reader. To gain the whole picture you have to work hard, flicking to and fro to gain a better understanding. I also feel like have only received half the story with the authors only presenting certain aspects of the genome, therefore not providing a full perspective of the capabilities of these microbes. Although if they did, it may be even harder to read. As well as this they give details of the genome in the results section but do not justify the relevance in the discussion. Despite these negatives, this paper is still important in demonstrating the presence of nutrient cycle associated bacteria within this deep sea sponge. Especially how they could be involved in scavenging of products potentially provided by the sponge and in return provide carbohydrates.

Tian, R. M., Sun, J., Cai, L., Zhang, W. P., Zhou, G. W., Qiu, J. W., & Qian, P. Y. (2016). The deep‐sea glass sponge Lophophysema eversa harbours potential symbionts responsible for the nutrient conversions of carbon, nitrogen and sulfur. Environmental microbiology.