Method optimization for denaturing gradient gel electrophoresis (DGGE) analysis of microflora from Eucalyptus sp. wood chips intended for pulping

Eucalyptus is the predominant exotic wood species used in South African pulp and paper industry. Once chipped and stored in piles, the wood becomes vulnerable to microbial degradation and spontaneous combustion. The denaturing gradient gel electrophoresis (DGGE) technique was optimized for the detection of microbial diversity in the wood. Wood chips were collected and milled to different specifications. The 16S and 18S rRNA genes were amplified using 338F-GC/518R and 933F-GC/1387R for bacteria and NS26/518R-GC and EF4F/518R for fungi. Several gel gradients were examined to determine optimal separation. A comparison of DGGE profiles revealed greater diversity in the milled wood chips amplified using primer sets of 338F-GC/518R (16S) and NS26/518R-GC (18S) with gradients of 30/60% (16S) and 25/50% (18S), respectively. Once optimized, this protocol was tested against five samples to assess its applicability to wood chip samples. Profiles were generated and amplicons excised from gels, re-amplified and sequenced to determine origin of DNA. Using this technique, 18 bacterial and 12 fungal species were identified, compared to ten bacterial and nine fungal isolates which were identified using the culturing technique and standard rRNA gene sequence analysis.  The optimised DGGE is an appropriate tool for microbial community studies of Eucalyptus wood chips.   Key words: Wood chips, Eucalyptus, community analysis using denaturing gradient gel electrophoresis (DGGE), microfloral variations.