Potential Interactions of Particle-Associated Anammox Bacteria with Bacterial and Archaeal Partners in the Namibian Upwelling System

Nitrogen is often considered a factor that limits the growth rate of phytoplankton. A high proportion of nitrogen loss (30-50%) occurs in oxygen minimum zones (OMZ) such as the Nambian Shelf, partially due to micro-organisms that carry out anaerobic oxidation of ammonium (anamox species). Previous research has been carried out into anamox species that reside in the Nambian Shelf under conditions that are similar to that near sewage systems, which contain more ammonium than naturally occurs in these waters. Woebken et al (2007) investigated the distribution and particle association of anamoxx species to improve understanding of their occurrence in their natural habitat. This topic is worthy of investigation because of the importance of the phytoplankton species influenced by the activity of anamox species.

Water samples containing bacterioplankton were collected from 4 stations around the Nambian Shelf, and water at 6 stations along a transect (23.0°S from 14.36°E to 12.0°E) were investigated. Profiles were created in terms of turbidity, oxygen levels and ammonium levels. Correlation was seen between anamox numbers and particulate organic carbon, and particulate organic nitrogen. Anamox species were present in depths of 30 m down to the sediment, across suboxic to anoxic conditions but not oxic, with the highest concentrations occurring near the coast.
            DNA from collected water samples was isolated, then replicated using PCR with universal bacterial and archaeal primers for the 16S rRNA sequences. The results were used to choose specific primers for a second PCR and specific probes from FISH and CARD-FISH (Catalyzed reporter deposition Fluorescence In Situ Hybridization).
            From the second PCR, they created several bacterial clonal libraries from the water samples at station 182 (119 m and 130 m deep) and one archaeal library based on samples from station 182 (130 m deep). The bacterial diversity and species numbers found were greater than that of Archaeal species: 235 bacterial species versus 23 archaeal species, belonging to 5 major groups as opposed to only 2 major groups for archaeal species. Several sequences were found to belong to uncultured bacteria. The species identified occur worldwide.
            FISH and CARD-FISH performed using group- and species-specific probes found a majority of bacteria (56.3%) occurred in clusters; 24.5% attached to particles; and 19.3% were individual cells.
            In situ observations were also carried out in the water column through a remotely operated camera, showing high densities of macroparticles.

This research shows the ability for anamox species to inhabit a wide range of habitats, limited by high oxygen levels. Their reliance on nitrogen suggests that natural cycles in terms of population numbers occur due to their removal of nitrogen as their numbers increase. It would be interesting to investigate the interactions between the cells considering they seem to flourish in group situations, such as quorum sensing, co-operative metabolism and gene transfer. Perhaps it is inter-bacterial interactions that allow them to inhabit regions with varying environmental conditions? If these species prove problematic for valuable species of phytoplankton it may be beneficial to consider research into breaking down these aggregates. Future methods of collection that did not disturb the aggregates may provide a more accurate representation of the frequency of clusters.

Woebken, D; Fuchs,B. M; Kuypers,M. M.M. and Amann, R. (2007) Potential Interactions of Particle-Associated Anammox Bacteria with Bacterial and Archaeal Partners in the Namibian Upwelling System Appl Environ Microbiol. 73(14): 4648–4657.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1932835/

Megan