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Applied and Environmental Microbiology, March 2001, p. 1318-1327, Vol. 67, No. 3
Max-Planck-Institut für Terrestrische
Mikrobiologie, D-35043 Marburg, Germany
Received 27 July 2000/Accepted 27 November 2000
Rice straw is a major substrate for the production of methane, a
greenhouse gas, in flooded rice fields. The bacterial community degrading rice straw under anoxic conditions was investigated with
molecular methods. Rice straw was incubated in paddy soil anaerobically
for 71 days. Denaturing gradient gel electrophoresis (DGGE) of the
amplified bacterial 16S rRNA genes showed that the composition of the
bacterial community changed during the first 15 days but then was
stable until the end of incubation. Fifteen DGGE bands with different
signal intensities were excised, cloned, and sequenced. In addition,
DNA was extracted from straw incubated for 1 and 29 days and the
bacterial 16S rRNA genes were amplified and cloned. From these clone
libraries 16 clones with different electrophoretic mobilities on a DGGE
gel were sequenced. From a total of 31 clones, 20 belonged to different
phylogenetic clusters of the clostridia, i.e., clostridial clusters I
(14 clones), III (1 clone), IV (1 clone), and XIVa (4 clones). One
clone fell also within the clostridia but could not be affiliated to
one of the clostridial clusters. Ten clones grouped closely with the
genera Bacillus (3 clones), Nitrosospira (1 clone), Fluoribacter (1 clones), and
Acidobacterium (2 clones) and with clone sequences
previously obtained from rice field soil (3 clones). The relative
abundances of various phylogenetic groups in the rice straw-colonizing
community were determined by fluorescence in situ hybridization (FISH). Bacteria were detached from the incubated rice straw with an efficiency of about 80 to 90%, as determined by dot blot hybridization of 16S
rRNA in extract and residue. The number of active (i.e., a sufficient
number of ribosomes) Bacteria detected with a general eubacterial probe (Eub338) after 8 days of incubation was 61% of the
total cell counts. This percentage decreased to 17% after 29 days of
incubation. Most (55%) of the active cells on day 8 belonged to the
genus Clostridium, mainly to clostridial clusters I (24%),
III (6%), and XIVa (24%). An additional 5% belonged to the
Cytophaga-Flavobacterium cluster of the
Cytophaga-Flavobacterium-Bacteroides phylum, 4% belonged
to the
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.3.1318-1327.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Bacterial Populations Colonizing and Degrading Rice
Straw in Anoxic Paddy Soil
,
, and
Proteobacteria, and 1.3% belonged
to the Bacillus subbranch of the gram-positive bacteria with a low G+C content. The results show that the bacterial community colonizing and decomposing rice straw developed during the first 15 days of incubation and was dominated by members of different clostridial clusters, especially clusters I, III, and XIVa.
*
Corresponding author. Mailing address:
Max-Planck-Institut für Terrestrische Mikrobiologie,
Karl-von-Frisch-Strasse, 35043 Marburg, Germany. Phone: 49 (6421) 178 801. Fax: 49 (6421) 178 809. E-mail:
conrad{at}mailer.uni-marburg.de.
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