Isolation of environmental bacteria with potential for remediation processes from anaerobic sediments from Reconquista river

PORZIONATO NATALIA; MELLOTA MARIANGELES; CURUTCHET GUSTAVO

Rosario

Congreso; IX Congreso de Microbiología General SAMIGE; 2013

SAMIGE

The Reconquista river, located at Buenos Aires surroundings is a highly polluted stream. The sediments of the river have high concentrations of heavy metals involved in mobilization-inmobilization processes that are mainly biocatalizated by anaerobic and aerobic microorganisms such as dissimilatory sulphate, iron(III) and manganese(IV) reducing bacteria and sulphur oxidizing bacteria. The aim of present work was the isolation and characterization of native environmental bacteria that are involved in metal mobilization redox processes. Superficial samples of the sediment were taken with a core sampler among of 0–20 cm of depth. Composite samples were taken with a shovel from surface to 30 cm depth and conserved in sterile polyethylene flasks with their initial moisture content. Chemical characterization of sediments showed high organic matter and sulphide content as it was expected in anoxic environments. Zn and Cu concentrations were found out over passing the reference values on sediments. In enrichment cultures, four groups of bacteria were isolated stimulating the propitious growth conditions in each case. Iron and sulphur oxidizing consortia were obtained from aerobic conditions at 9K and 0K media respectively, and iron and sulphate reducing bacteria consortia were obtained from anoxic conditions at Postgate C media and in a modified Postgate C media with ferrous chloride in sodium sulphate replacement. Kinetic growth studies of the isolates were carried out by measuring population using Thoma chamber and phase contrast microscopy, substrate consumption and product apparition rate. Oxidizing consortia experiments exhibited acidification caused by sulphur oxidation processes and ferrous iron conversion to ferric iron ore by Fe(II) oxidation processes. Reducing consortia cultures exhibited the apparition of a black precipitate (iron sulphide) that suggested the activity of reducing indigenous bacteria. In case of dissimilatory Fe(III) reduction experiments, rise in soluble iron(II) concentration was detected. The four isolates have important catalytic activities in biogeochemical cycles in sediments and their metabolism is involved in redox processes of metal mobility. Reduction processes are plentiful at contaminated urban streams where sulphate and organic matter availability is high, and so they are the sulphate-sulphide conversion and ferrous iron compounds formation reactions. At these conditions prevails precipitation of metals as sulphides or hydroxides and its adsorption to the sediment matrix. Oxidation processes predominates in oxygen exposition conditions generated by anthropogenic disturbances of the sediment such as dredging operation. In this case the acidification caused by sulphur sulphides oxidation catalyzed by authothrofic bacteria derives in metal leaching, increasing contaminant bioavailability. These biocatalyzed processes have extreme importance in risk assessment and development of remediation tools.