Investigation of bacterial community composition and abundance in a lowland arable catchment

This study aimed to characterise the bacterial community composition and abundance in the River Wensum in Norfolk using epifluorescence microscopy (EFM), automated ribosomal intergenic analysis (ARISA) and 454 pyrosequencing. It also aimed to determine the effects of spatial and temporal variations and environmental factors on bacterial community composition and abundance in this intensively farmed lowland catchment. The three techniques provided the same trends in bacterial community composition and abundance across the Wensum catchment. Total bacterial numbers ranged from 0.21 × 106 cells/mL to 5.34 × 106 cells/mL (mean = 1.1 × 106 cells/mL). The bacterial community composition and abundance showed significant differences between sites and times and were related to environmental parameters, with temperature and flow rate explaining most of the variation in bacterial community composition and abundance. Bacterial abundance increases as water moves downstream, while bacterial diversity decreases as water moves downstream. Some operational taxonomic units (OTUs) become commoner as the water moves downstream (3rd and 4th order streams). This presumably reflects the fact that these bacteria are actively growing in the river, and reducing the abundance of other taxa. Consequently, the community becomes less diverse moving downstream, although a small number of sites do not fit this pattern. The River Wensum is dominated by the phyla Proteobacteria, Bacteroidetes, Cyanobacteria and Actinobacteria. Members of these phyla are well known to be responsible for biogeochemical processes, such as nitrogen cycling. The commonest bacteria at upstream sites were Proteobacteria (OTUs 2 and 4), Deltaproteobacteria (OTU29), Gammaproteobacteria (OTU32), Sphingobacteria (OUT9) and Flavobacteria (OTUs 12 and 23). Most OTUs (2, 9, 17, 29 and 32) are considered to be soil bacteria, suggesting that these bacteria are terrestrial in origin and are flushed into the lower order streams. Most of the upstream bacteria showed positive relationships with total nitrogen (TN) and total carbon (TC) and the presence of arable areas. On the other hand, the commonest bacteria at downstream sites were Cyanobacteria (OTU1), Flavobacteria (OTUs 3, 10 and 19), Cytophagia (OTU14), Actinobacteria (OTUs 20, 21 and 25) and Alphaproteobacteria (OTU26). Most of the downstream bacterial OTUs showed a positive relationship with TP and the presence of urban areas. The results of this research, however, do not provide strong evidence that competition is an important process structuring these bacterial communities. In addition, the correlations between environmental parameters and bacterial composition and abundance are not strong and do not clearly distinguish the most impacted sites from others. This suggests that bacterial community composition cannot be used as an indicator of the ecological status to assess compliance with Water Framework Directive (WFD) in a moderately impacted lowland catchment like the Wensum.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Albaggar, Ali

Language dc:language

en