Two broad communities can be distinguished in marine systems, those attached to amorphous aggregate material dispersed throughout the water column and those that are freely suspended in the water column (planktonic). It has been suggested that two distinct microbial populations are associated with each habitat due to phenotypic adaptation to the different conditions in aggregates and the surrounding water. The aim of this study was to investigate the diversity of aggregate-associated and planktonic marine ammonia oxidisers (AOBs - the organisms responsible for the rate limiting step in nitrification) in both natural environments and laboratory-reared systems and to determine whether aggregate material selected for particular groups of AOBs. Detection of AOBs relied heavily on the use of molecular analysis of extracted DNA. Thus, a preliminary study was performed to assess whether preferential lysis occurred when representatives of both genera within the B-subgroup AOBs {Nitrosospira multiformis and Nitrosomonas europaea) were exposed to lysis procedures commonly applied to marine samples. Minimal bias existed, with Nitrosomonas europaea proving to be less susceptible to lysis only when the lytic agents (sodium dodecyl sulphate and lysozyme) were absent or at concentrations 100-fold less than those applied in routine environmental extraction. Environmental populations of aggregate-associated and planktonic AOBs in the NW Mediterranean Sea were assessed in summer and winter at stations both within and beyond regions of fresh water inflow (the plume). Molecular analysis involved amplification, by the polymerase chain reaction, of 16S rRNA genes from extracted DNA using AOB-specific primers. Analysis of 16S rDNA sequences coupled with DGGE and specific probing revealed temporal and spatial effects in community structure of AOBs. In the summer, genus level selection of AOBs was observed with Nitrosospira dominating in the aggregate population and Nitrosomonas dominating in the planktonic phase. This was found in the surface waters of geographically distant sites within and outside the plume. Between-site differences were evident in the deeper waters with Nitrosospira-like sequences more abundant in plume diluted waters and Nitrosomonas like sequences more abundant outside this zone, while genus level selection between aggregate-associated and planktonic communities was not detected. In winter, a uniform pattern of AOB distribution emerged with an even distribution of two Nitrosospira sequences at each site on all aggregate and planktonic samples. The AOB community structure of sediment samples was not wholly resolved by application of direct molecular techniques and the culturable diversity was later examined by an enrichment-based approach. A laboratory-reared aggregate system was developed to assess the distribution and selection of inoculated pure and enrichment cultures of AOBs and to assess the effect of sampling technique on the observed community structure. Enclosed vessels containing North Sea water were rotated until aggregation of autochthonous particulate material formed discrete aggregates. No genus level selection of AOBs was observed in aggregate-associated and planktonic communities in North Sea water yet differences in the distribution of closely related sequences within cluster 1 Nitrosospira were observed between the two communities. Observed aggregate and planktonic community structure was affected by the method used to separate the two fractions. Active bacterial production was not necessary for aggregate formation if a pooled suspension of aggregates was sterilised and added to a medium of cell-free filtered sea water. Thus, the successful inoculation and retrieval of an N. multiformis culture within the cell free system suggested that it was appropriate for investigation of the colonisation dynamics of inoculated AOBs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:327297 |
| Date | January 2000 |
| Creators | Cuschieri, Katie Sarah |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602054 |
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