title: Phosphorus chemistry and bacterial community composition interact in brackish sediments receiving agricultural discharges.
abstract: BACKGROUND
  External nutrient discharges have caused eutrophication in many estuaries and coastal seas such as the Baltic Sea. The sedimented nutrients can affect bacterial communities which, in turn, are widely believed to contribute to release of nutrients such as phosphorus from the sediment.
  
  
  METHODS
  We investigated relationships between bacterial communities and chemical forms of phosphorus as well as elements involved in its cycling in brackish sediments using up-to-date multivariate statistical methods. Bacterial community composition was determined by terminal restriction fragment length polymorphism and cloning of the 16S rRNA gene.
  
  
  CONCLUSIONS
  The bacterial community composition differed along gradients of nutrients, especially of different phosphorus forms, from the estuary receiving agricultural phosphorus loading to the open sea. This suggests that the chemical composition of sediment phosphorus, which has been affected by riverine phosphorus loading, influenced on bacterial communities. Chemical and spatial parameters explained 25% and 11% of the variation in bacterial communities. Deltaproteobacteria, presumptively sulphate and sulphur/iron reducing, were strongly associated to chemical parameters, also when spatial autocorrelation was taken into account. Sulphate reducers correlated positively with labile organic phosphorus and total nitrogen in the open sea sediments. Sulphur/iron reducers and sulphate reducers linked to iron reduction correlated positively with aluminium- and iron-bound phosphorus, and total iron in the estuary. The sulphate and sulphur/iron reducing bacteria can thus have an important role both in the mineralization and mobilization of nutrients from sediment.
  
  
  CONCLUSIONS
  Novelty in our study is that relationships between bacterial community composition and different phosphorus forms, instead of total phosphorus, were investigated. Total phosphorus does not necessarily bring out interactions between bacteria and phosphorus chemistry since proportions of easily usable mobile (reactive) phosphorus and immobile phosphorus forms in different sediments can vary. Our study suggested possible feedbacks between different forms of phosphorus and bacterial community composition.
authors: Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland.
authors: Hanna
authors: H
authors: Sinkko
authors: Kaarina
authors: K
authors: Lukkari
authors: Abdullahi S
authors: AS
authors: Jama
authors: Leila M
authors: LM
authors: Sihvonen
authors: Kaarina
authors: K
authors: Sivonen
authors: Mirja
authors: M
authors: Leivuori
authors: Matias
authors: M
authors: Rantanen
authors: Lars
authors: L
authors: Paulin
authors: Christina
authors: C
authors: Lyra
mesh_terms: D000383:Agriculture; D001419:Bacteria / Q000145:classification / Q000378:metabolism*; D004777:Environment; D005246:Feedback; D019015:Geologic Sediments / Q000382:microbiology*; D009792:Oceans and Seas; D010758:Phosphorus / Q000737:chemistry* / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism
chemical_list: D013431:Sulfates; D010758:Phosphorus