Barak Vasker ID Marine Biotechnology Keuter et al. 2011

Introduction  Recirculation Aquaculture Systems (RAS) in which waste of aquaculture is processed. Water and “safe” nutrients re-used.  In the biofilter, dense biofilm will be created on carrier elements (“moving bed”), mostly comprising of: Ammonium Oxidizing Bacteria (AOB) & Nitrite Oxidizing Bacteria (NOB) working together as a pair.

Introduction  Nitrospira sp. Is a curved rod. Usually single celled, but also capable of colonization (biofilm). Non-obligatory autotrophs.  NH 4 +  NO 2 -  NO 3 (Requires aerobic atmosphere).  Dominant NOB, optimal activity and mechanism was not well understood, in part due to low energy yields of Ammonia oxidation and even lower yields on Nitrite oxidation (total work ~ 6 years (!)).

Introduction  Chemotaxonomic identification of Nitrospira sp. (Lipski 2001) via FAME (Fatty Acid Methyl Ester) Markers: 1)16:1 cis 7 2)16:1 cis 11

Results  Nitrospira cells were repeatedly diluted, enriched and transferred to fresh medium. This process repeated several times, until a new strain was isolated: “Ecomares 2.1”. (even pure, still secrets a tough polymer)  16S rRNA sequences clones were retrieved (1502 bp).  13 C-bicarbonate labeled fatty acids shows Nitrospira’s role.

Results  What about the 16S rRNA?  Ecomares 2.1 (isolated in Büsum, Germany) was found to match at most 99.1 % of the sequence of Nitrospira in Rehovot, Israel.  All strains showed are a part of cluster IV.

Results  Nitrospira colonies (circled) & nitrosomonas (marked “X”) colonies function as a pair, with each one enjoying the other’s produce. (mutualism?)

Discussion  High Nitrogenic load should have selected Nitrobacter (or other proteobacteria), consistent with recent strategy theories. How can Nitrospira dominate the RAS? Lab procedures/conditions. Theory / de-facto not always consistent.  Who is the most durable strain to high nitrite concentrations? Could this be enough to establish dominance? Pure Ecomares 2.1 still coated with thick, tough polymer.

Discussion  Selective Shear forces inside RAS? A stronger adherence of Nitrospira might be the final blow.  What is happening in other marine RAS? 16S rRNA sequences from other marine RAS suggest Nitrospira dominance.

Conclusions  Nitrospira-like bacteria dominates RAS biofilters, in contrast to what previously thought. Nitrospira characteristics critical for Marine aquaculture systems.  Nitrospira is supported by Nitrosomonas in an AOB/NOB biofilm.  Nitrospira Ecomares 2.1 is the most resisting strain to nitrite peaks in RAS. Therefore, it’s favorable in establishing dominance as the major Nitrite Oxidizing Bacteria (NOB) of the Biofilm.

Conclusions  Physiology is still under-investigated. Further research will reveal metabolic pathways, inhibatory effects & optimization of the process. We might be able to get different bacteria strains growing in different conditions.

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Thank you !