Production of gellan gum, an exopolysaccharide, from biodiesel-derived waste glycerol by Sphingomonas spp.

In the present study, biodiesel-derived waste glycerol (WG) was used for the isolation and production of gellan, an exopolysaccharide, on media containing WG as the main carbon source. Two bacterial isolates showed gellan producing potential which were identified as Sphingomonas pseudosanguinis (Accession No. GI:724472387) and Sphingomonas yabuuchiae (GI:724472388) by 16S rRNA gene sequencing. To maximize gellan production by S. pseudosanguinis and S. yabuuchiae, media optimization was performed at different pHs and glycerol concentrations. Morphological observations through microscopic images showed the production of gellan from these isolates. Simple linear regression showed better utilization of WG by S. pseudosanguinis than S. yabuuchiae at pH 6 and pH 7. Though, both the strains showed reverse trend at pH 8. Both the strains were able to produce high amounts of gellan gum (51.6 and 52.6 g/l, respectively) using WG (80 g/l) as the sole carbon source, in a minimal medium. This is the first report on the efficient degradation of WG and low-cost production of gellan. Owing to these characteristics, S. pseudosanguinis and S. yabuuchiae demonstrate great potential for use in the commercial production of gellan and in the bioremediation of WG.

Biodegradation of glycerol using bacterial isolates from soil under aerobic conditions.

Glycerol, a non-biodegradable by-product during biodiesel production is a major concern to the emerging biodiesel industry. Many microbes in natural environments have the ability to utilize glycerol as a sole carbon and energy source. The focus of this study was to screen for microorganisms from soil, capable of glycerol utilization and its conversion to value added products such as ethanol and 1,3-propanediol (1,3-PDO). Twelve bacterial isolates were screened for glycerol utilization ability in shake flask fermentations using M9 media supplemented with analytical grade glycerol (30 g/L) at various pH values (6, 7 and 8) and temperatures (30°C, 35°C and 40°C). Among these, six bacterial isolates (SM1, SM3, SM4, SM5, SM7 and SM8) with high glycerol degradation efficiency (>80%) were selected for further analysis. Highest level of 1,3-PDO production (15 g/L) was observed with isolate SM7 at pH 7 and 30°C, while superior ethanol production (14 g/L) was achieved by isolate SM9 at pH 8 and 35°C, at a glycerol concentration of 30 g/L. The selected strains were further evaluated for their bioconversion efficiency at elevated glycerol concentrations (50-110 g/L). Maximum 1,3-PDO production (46 g/L and 35 g/L) was achieved at a glycerol concentration of 70 g/L by isolates SM4 and SM7 respectively, with high glycerol degradation efficiency (>90). Three isolates (SM4, SM5 and SM7) also showed greater glycerol tolerance (up to 110 g/L). The isolates SM4 and SM7 were identified as Klebsiella pneumoniae and SM5 as Enterobacter aerogenes by 16S rDNA analysis. These novel isolates with greater glycerol tolerance could be used for the biodegradation of glycerol waste generated from the biodiesel industry into value-added commercial products.