A comparative analysis of microflora during biofilm development on grape seeds exposed to methanol in a biofilter

The attachment of microorganisms onto biotic surfaces to form biofilm structures on the support media of a biofilter has great impact on biodegradation systems. This study examined the composition of the microbial community that developed on grape seeds (GS) used as support media in methanol degradation biofilters. They were analyzed using conventional microbiology techniques and API galleries. Analysis of microbial counts showed that, in GS before methanol exposure, bacteria and filamentous fungi were predominant over yeasts. In contrast, GS exposed to methanol exhibited more bacteria and yeasts than fungi. Most of the Gram-negative bacteria were the Pseudomonas genus, Bacillus staerothermophilus, Bacillus amyloliquefaciens, and Bacillus pumilus. Rhodotorula mucilaginosa was the primary yeast found. The filamentous fungi Aspergillus sp. Cladosporium cladosporioides, Fusarium sp., and Alternaria sp. were also detected. No Gram-positive bacteria growth was found on GS exposed to methanol. Using scanning electron microscopy, biofilm formation on the GS was examined to reveal the presence of both prokaryotic and eukaryotic microorganisms as biomass accumulation was visible on the seeds. Seeds exposed to methanol for 90 days showed a mature biofilm with cuticle and epidermal layer decline, as well as biofilm dissolution into grape seed integuments.