SummaryPectinolytic microorganisms involved in the water retting process were characterized. Cultivable mesophilic anaerobic and aerobic bacteria were isolated from unretted and water-retted material. A total of 104 anaerobic and 23 aerobic pectinolytic strains were identified. Polygalacturonase activity was measured in the supernatant of cell cultures; 24 anaerobic and nine aerobic isolates showed an enzymatic activity higher than the reference strains Clostridium felsineum and Bacillus subtilis respectively. We performed the first genotypic characterization of the retting microflora by a 16S amplified ribosomal DNA restriction analysis (ARDRA). Anaerobic isolates were divided into five different groups, and the aerobic isolates were clustered into three groups. 84.6% of the anaerobic and 82.6% of the aerobic isolates consisted of two main haplotypes. Partial 16S rRNA gene sequences were determined for 12 strains, representative of each haplotype. All anaerobic strains were assigned to the Clostridium genus, whereas the aerobic isolates were assigned to either the Bacillus or the Paenibacillus genus. Anaerobic isolates with high polygalacturonase (PG) activity belong to two clearly distinct phylogenetic clusters related to C. acetobutylicum-C. felsineum and C. saccharobutylicum species. Aerobic isolates with high PG activity belong to two clearly distinct phylogenetic clusters related to B. subtilis T and B. pumilus T .

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Retting is the major limitation to an efficient production of textile hemp fibres. Traditional retting has been carried out by autochthonous bacterial community. Aerobic and anaerobic pectinolytic strains were isolated from hemp or flax sources and characterised. Anaerobic pectinolytic strains had a wide range of acid polygalacturonase (PG) activity, whereas aerobic isolates did not produce any acid PG activity, but only an alkalophylic one, suggesting they could play a minor role in the retting process, except in the early stages. Analysis of 16S rDNA sequences assigned anaerobic strains to the Clostridium genus and aerobic isolates to the Bacillus and Paenibacillus genus. C. felsineum and C. acetobutylicum were confirmed as the main anaerobic agents. Nevertheless, a high proportion of anaerobic and aerobic pectinolytic strains was assigned to C. saccharobutylicum and B. pumilus, respectively, both species never being described as involved in water retting. Anaerobic and aerobic strains with high PG activity were selected and characterized. PG activity is well correlated with the strain retting efficiency and improvement of the process was obtained by inoculating the retting water with spores of selected aerobic and anaerobic bacteria. An advisable feature of retting strains is the absence of cellulosolytic activity. An aerobic strain with no cellulosolytic activity was identified. In contrast, all the anaerobic isolates showed cellulosolytic activity. Mutagenesis was ineffective for selection of Cel-Pec+ mutants. Localization of the C. felsineum L1/6 PG activity was investigated