Abstract
BackgroundAmong themophilic consolidated bioprocessing (CBP) candidate organisms, environmental isolates of Clostridium clariflavum have demonstrated the ability to grow on xylan, and the genome of C. clariflavum DSM 19732 has revealed a number of mechanisms that foster solubilization of hemicellulose that are distinctive relative to the model cellulolytic thermophile Clostridium thermocellum.ResultsGrowth experiments on xylan, xylooligosaccharides, and xylose reveal that C. clariflavum strains are able to completely break down xylan to xylose and that the environmental strain C. clariflavum sp. 4-2a is able to grow on monomeric xylose. C. clariflavum strains were able to utilize a larger proportion of unpretreated switchgrass, and solubilize a higher proportion of glucan, xylan, and arabinan, with strain 4-2a reaching the highest extent of solubilization of these components (64.7 to 69.4%) compared to C. thermocellum (29.5 to 42.5%). In addition, glycome immunoanalyses of residual plant biomass reveal differences in the extent of degradation of easily accessible xylans, with C. clariflavum strains having increased solubilization of this fraction of xylans relative to C. thermocellum.ConclusionsC. clariflavum strains exhibit higher activity than C. thermocellum in the breakdown of hemicellulose and are capable of degrading xylan to xylooligomers and xylose. This capability seems to also play a role in the higher levels of utilization of unpretreated plant material.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0136-4) contains supplementary material, which is available to authorized users.
Highlights
Among themophilic consolidated bioprocessing (CBP) candidate organisms, environmental isolates of Clostridium clariflavum have demonstrated the ability to grow on xylan, and the genome of C. clariflavum DSM 19732 has revealed a number of mechanisms that foster solubilization of hemicellulose that are distinctive relative to the model cellulolytic thermophile Clostridium thermocellum
In an effort to expand the known metabolic diversity of this species, we have previously described the enrichment and isolation of novel C. clariflavum strains from thermophilic compost, and reported on their ability to grow on xylan, which is a key differentiating capability compared to DSM 19732 [2,7]
C. thermocellum inocula were able to hydrolyze xylan to xylooligomers, but were not able to grow on xylan or produce any detectable xylose (Figure 1A)
Summary
Among themophilic consolidated bioprocessing (CBP) candidate organisms, environmental isolates of Clostridium clariflavum have demonstrated the ability to grow on xylan, and the genome of C. clariflavum DSM 19732 has revealed a number of mechanisms that foster solubilization of hemicellulose that are distinctive relative to the model cellulolytic thermophile Clostridium thermocellum. It is curious to note, that the model thermophile Clostridium thermocellum and several of its close relatives do not grow on hemicellulose or its component pentose sugars. In an effort to expand the known metabolic diversity of this species, we have previously described the enrichment and isolation of novel C. clariflavum strains from thermophilic compost, and reported on their ability to grow on xylan, which is a key differentiating capability compared to DSM 19732 [2,7]. The genome of C. clariflavum DSM 19732 reveals a very distinct mechanism for the breakdown of hemicellulose, as compared to its close relative C. thermocellum [8]
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