A closer look on the genome sequence of C. flavigena
revealed a set of genes which are probably responsible for the yellowish color of C. flavigena
cells by encoding enzymes that are involved in the synthesis of carotenoids. Carotenoids are produced by the action of geranylgeranyl pyrophosphate synthase (Cfla_2893), squalene/phytoene synthase (Cfla_2892), phytoene desaturase (Cfla_2891), lycopene cyclase (Cfla_2890, Cfla_2889) and lycopene elongase (Cfla_2888). Cfla_2893 is declared as a pseudo gene, but when ignoring the frame shift the deduced amino acid sequence shows significant similarity to geranylgeranyl pyrophosphate synthases. Geranylgeranyl pyrophosphate synthases start the biosynthesis of carotenoids by combining farnesyl pyrophosphate with C5
isoprenoid units to C20
-molecules, geranylgeranyl pyrophosphate. The phytoene synthase catalyzes the condensation of two geranylgeranyl pyrophosphate molecules followed by the removal of diphosphate and a proton shift leading to the formation of phytoene. Sequential desaturation steps are conducted by the phytoene desaturase followed by cyclisation of the ends of the molecules catalyzed by the lycopene cyclase [45
]. It is remarkable that the genes belonging to the putative carotenoid biosynthesis clusters of Beutenbergia cavernae
], Leifsonia xyli
) and Sanguibacter keddieii
] have a similar size and show the same organization as in the genome of C. flavigena
In the eighth edition of Bergey’s manual the members of the genus Cellulomonas
are described as motile by one or a few flagella or non-motile, even within the genus both characteristics occur [32
]. Regarding the motility of C. flavigena
there are different observations described. Thayer et al.
(1984) report the existence of polar multitrichous flagella [31
], whereas Stackebrandt et al.
(1979) and Schaal (1986) reported C. flavigena
as non-motile [3
]. In contrast to Thayer’s observation we found no genes coding proteins belonging to the category ‘flagellum structure and biogenesis’ in the genome sequence. Kenyon et al.
(2005) report for the genus Cellulomonas
a coherency between the production of curdlan, a β-1,3-glucan, and non-motility. They observed that the production of curdlan EPS by the non-motile C. flavigena
leads to a closer adherence to cellulose and hemicellulose. In contrast, cells of the motile Cellulomonas
strain C. gelida
produce no curdlan EPS and are not directly attached to the cellulose fibers [28
]. The production of curdlan by C. flavigena
is consistent with the observation of 17 glycosyl transferases (GT) belonging to family 2, as β-1,3-glucan synthases are often found in this GT family.
The characteristic attribute of C. flavigena
and the other members of the genus Cellulomonas
is the ability to degrade cellulose, xylan and starch. The most molecular work has been done on cellulase and xylanase genes from C. fimi
, but also cellulases, xylanases and chitinases of C. flavigena
were identified and characterized [49
]. The genome sequence and the subsequent annotation revealed that 9.6% of encoded proteins are classified into the COG category ‘carbohydrate transport and metabolism’. Among them several genes coding for xylan degrading enzymes; 14 genes coding for putative endo-1,4-β-xylanases belonging to glycoside hydrolase family 10 and five genes encoding β-xylosidases. For the hydrolysis of cellulose the concerted action of endo-1,4-β-glucanases, 1,4-β-cellobiohydrolases and β-glucosidases is necessary. Endo-1,4-β-glucanases randomly cleave within the cellulose molecule and increase the number of non-reducing ends which are attacked by 1,4-β-cellobiohydrolases. The released cellobiose is cleaved by β-glucosidases. In the genome of C. flavigena
two genes coding endo-1,4-β-glucanases (Cfla_0016, Cfla_1897), three genes encoding 1,4-β-cellobiohydrolases (Cfla_1896, Cfla_2912, Cfla_2913) and three genes coding β-glucosidases (Cfla_1129, Cfla_3027, Cfla_2913) were identified.