Microbial exopolymers in sediments of a second order stream: Njoro River Kenya

Abstract

Determinations of concentrations of various carbohydrates associated with sedimentary biofilms were carried out in Njoro River between October 1998 and December 1999 in a muddy and sandy site. Significant temporal differences (P < 0.05) were observed for muddy site. Temporal differences for total colloidal carbohydrates (TCHO) were attributed to particulate organic matter (POM) and dissolved organic matter (DOM) imports in the wet seasons while increase in concentrations of colloidal carbohydrates (Coll EDTA) during the dry season was attributed to biofilms and low molecular weight non polymeric material such as simple sugars and leacheates from mycrophytobenthic primary production in the first few millimeters of sediment. Results indicated significant correlations between various carbohydrates with sediment parameters such as grain sizes, total organic nitrogen (TON) and total organic carbon (TOC) but only exopolymeric substances (EPS) (ethanol fraction of colloidal EDTA) were correlated to bacterial abundances. This implied that EPS is mainly of bacterial origin while TCHO and Coll EDTA fractions are from the pool of organic matter in sediments. EPS constituted about 30% of Coll EDTA carbohydrates at both sites. This means that a big proportion of stream bed biofilms is constituted of bacteria thus highlighting their importance in stream ecology and especially their roles in the self purification properties and pollution elimination from streams.

Journal of Tropical Microbiology and Biotechnology Vol. 2(1) 2006: 37−45