Monday, November 13, 2006

Chromate Limits Carbon Source Utilization by Arthrobacter sp. FB24.

Weimin Chen, Megalena Kourteva, Allan Konopka, and Cindy Nakatsu. Purdue Univ, Dept of Agronomy, 915 West State St, West Lafayette, IN 47907-2054

Arthrobacter species are common soil bacteria that have been isolated from many diverse and often extreme environments. Recently our laboratory isolated a chromate resistant Arthrobacter species, strain FB24, from soils contaminated by elevated concentrations of both heavy metals (lead and chromium) and petroleum hydrocarbons. Inhibitory Cr(VI) concentrations differed with growth medium used, which could be a limiting factor in the survival of bacteria, even those possessing resistance mechanisms, in environments with different available carbon sources. Maximum levels of Cr(VI) (200-300mM) tolerance was observed using nutrient broth. The objective of this research is to investigate the nutritional factors limiting growth of FB24 in the presence of Cr(VI). The genome sequence of FB24 has been determined and BLAST analysis indicated the presence of genes potentially involved in aromatic hydrocarbon degradation, major carbon sources in soils from which FB24 was isolated. Growth experiments were performed and showed FB24 could use the hydrocarbons, phthalate, phenol, benzoate, and 3-, 4-, 3,4-, 2,5-, and 2,4-hydroxybenzoates as sole carbon sources. The possession or expression of genes for growth on hydrocarbons is not a limiting factor for this organism. Basic substrate utilization by FB24 determined using BIOLOG GP2 plates also indicated diverse metabolic capabilities. Preliminary growth experiments using defined media with single substrates, glucose, fructose and succinate, showed differential reduced growth in the presence of Cr(VI). Maximum Cr(VI) concentration tolerated was greater when glucose was used as substrate versus fructose but levels were 10-100 fold less than in nutrient broth. Addition of vitamins or casamino acids to the defined media improved resistance but still not to the level observed in nutrient broth. The results indicate that factor Cr(VI) limiting to growth in the presence of Cr(VI), is dependent on the carbon source, vitamins, casamino acids and at least another factor that we have yet to discover.