Insight into the carbohydrate metabolism in members of the genus Rhodococcus

HERNANDEZ MA; FLORES ML; ALVAREZ, HÉCTOR M

VILLA CARLOS PAZ

Congreso; VI Congreso Argentino de Microbiologia General (SAMIGE); 2009

SAMIGE

The genus Rhodococcus, which belongs to the actinomycetes group together with other related bacteria, such as Mycobacterium and Corynebacterium, are highly versatile microorganisms with the physiological capability to adapt to different environments. They occur in a diversity of natural environments such as in soil, water and marine sediments. Despite the ecological and biotechnological importance of this genus, the core metabolic strategy that permits cells to be successful in the environment has been poorly studied.     The purpose of this study was to examine some aspects of carbohydrate metabolism in species of Rhodococcus during both replicative and non-replicative stages. We explored the response of cells to diverse environmental conditions and performed a genome-wide bioinformatic analysis of genes involved in carbohydrate metabolism using the genome database of R. jostii RHA1. Moreover, we examined the ability of R. opacus and R. jostii strains to synthesize and accumulate polysaccharides under different conditions. The RHA1 genome contains all necessary genes/enzymes for both glycolytic pathways, the EMP- and ED-pathways, and for the pentose phosphate pathway. This suggests that cells rely on different alternatives for carbohydrates catabolism for sustained periods, depending on the fluctuating nutritional conditions of the environment. In addition, we identified all key genes for the biosynthesis and mobilization of glycogen in the R. jostii genome. In this context, R. jostii RHA1 and R. opacus PD630 were able to accumulate an intracellular polysaccharide after cultivation of cells on both, nutrient broth and minimal salts medium with gluconate as sole carbon source. The complete analysis of this polysaccharide revealed to be a glucose polymer, such as glycogen. We found that other species of the genus, such as R. ruber, R. fascians and R. erythropolis, were also able to accumulate glycogen. The studied strains accumulated glycogen during exponential growth phase and the content decreased during stationary growth phase. This result suggests that glycogen biosynthesis may deal with the sugar excess during exponential growth phase in these bacteria, and probably serve as a pool of sugars for using when necessary. When cells of R. opacus and R. jostii were incubated under desiccation conditions (non-replicative stage), we observed the production of an extracellular polymeric substance (EPS). Chemical analyses of the EPS from strain PD630 by diverse chromatographic methods and 1H-RMN revealed the occurrence of a polysaccharide polymer as main compound plus minor amounts of proteins and lipids. The carbohydrate fraction was composed by b-D-glucuronic acid, 2,3-a-D-mannose and minor amounts of glucose and xylose. The results of this study suggest that Rhodococcus bacteria are endowed with a robust, flexible and versatile carbohydrate metabolism, which is necessary for metabolically adapting to environments with fluctuating nutritional conditions.