Community shifts in a seeded 3-chlorobenzoate degrading membrane biofilm reactor: indications for involvement of in situ horizontal transfer of the clc-element from inoculum to contaminant bacteria.
Pseudomonas putida BN210, carrying the self- transferable clc-element encoding degradation of 3-chlorobenzoate on the chromosome, was used as inoculum in different membrane biofilm reactors treating 3-chlorobenzoate-contaminated model wastewater. Analysis of the bacterial population in the effluent and in the biofilm showed the loss of BN210 beyond detection from the reactors and the appearance of several novel 3-chlorobenzoate mineralizing bacteria mainly belonging to the beta-proteobacteria. In contrast, in non-inoculated reactors, no 3-chlorobenzoate degradation was observed and no 3-chlorobenzoate degraders could be recovered. Southern blots hybridization of genomic DNA using clc-element-specific probes and FIGE analysis indicated the presence of the complete clc-element in one or more copies in the isolates. Moreover, the isolates could transfer the clc genes to Ralstonia metallidurans recipients. Two representative reactor isolates, Ralstonia sp. strains KP3 and KP9 demonstrated a higher growth rate on 3-chlorobenzoate than strain BN210 in batch cultures. When BN210, KP3 and KP9 were simultaneously inoculated in a membrane reactor supplied with 3-chlorobenzoate, strain KP3 outcompeted the two other strains and remained the major 3-chlorobenzoate degrading population in the reactor. Our data suggest that in situ horizontal transfer of the clc-element from the inoculum to contaminant bacteria in the reactors was involved in the establishment of novel 3-chlorobenzoate degrading populations that were more competitive under the defined reactor conditions than the inoculum strain.
Springael
Dirk
D
Environmental Technology, Flemish Institute for Technological Research, B-2400 Mol, Belgium. dirk.springael@vito.be
Peys
Kurt
K
Ryngaert
Annemie
A
Van Roy
Sandra
S
Hooyberghs
Liliane
L
Ravatn
Roald
R
Heyndrickx
Marc
M
van der Meer
Jan-Roelof
JR
Vandecasteele
Carlo
C
Mergeay
Max
M
Diels
Ludo
L
D001673:Biodegradation, Environmental; D019149:Bioreactors / Q000382:microbiology*; D002723:Chlorobenzoates / Q000378:metabolism*; D022761:Gene Transfer, Horizontal; D005838:Genotype; D016946:Gram-Negative Aerobic Rods and Cocci / Q000235:genetics* / Q000378:metabolism*
D002723:Chlorobenzoates; C036427:3-chlorobenzoic acid