The strain was found to be a Gram-negative rod, nonmotile and nonspore forming. The strain could utilize arabinose, citrate, glucose, lactose, maltose, mannitol and xylose individually as sole carbon sources and was found to be catalase-positive, oxidase-positive, coagulase-positive, nitrate Akt inhibitor reductase-positive, urease-negative

and sensitive to chloramphenicol. On the basis of the above characteristics and other morphological, nutritional and biochemical features of these characteristics (Kloos & Schleifer, 1986; Smibert & Krieg, 1994), strain PWTJD was presumed to be an Ochrobactrum species. To confirm this identification, the partial 16S rRNA gene sequence (1374 bp) of the isolate was determined and deposited in the DDBJ/EMBL/GenBank with the accession no. HM056231. Analysis of that sequence using the blast search revealed 99.9% sequence similarity to Ochrobactrum anthropi LMG 3331T, Ochrobactrum cytisi ESC1T and Ochrobactrum lupini Lup21T. Although the combined analyses indicated a strong correlation at the genus level, a few differential biochemical properties of strain PWTJD were observed when compared with its closest members RG7422 in vitro of the genus Ochrobactrum and as such these data were not sufficient to identify the strain to the species level. Thus,

the bacterium has been identified as Ochrobactrum sp. strain PWTJD. Figure 1 shows the growth of strain PWTJD vis-à-vis degradation of phenanthrene under optimal conditions. The strain PWTJD could grow well in MSM at a pH range of 7.2–8.0 and at a temperature range of 25–30 °C. However, both the growth rate and the rate of phenanthrene (1 g L−1) utilization became slower when the pH of the medium was slightly acidic, but favored under a slightly alkaline condition with the optimum pH of 7.2 at 28 °C under shake culture conditions (180 r.p.m.). Although there was a short lag clonidine period during the initial incubation, the rate of degradation of phenanthrene rapidly

increased after 24 h of incubation and more than 99% of phenanthrene was found to be degraded within 7 days of incubation (Fig. 1). However, during growth on phenanthrene, the pH of the medium declined to as low as 6.8 from 7.2, indicating the possible accumulation of various transient acidic metabolites with time. Apart from phenanthrene, the strain PWTJD could also utilize 2-hydroxy-1-naphthoic acid, although at a much slower rate than that of phenanthrene and salicylic acid individually as sole sources of carbon and energy, but failed to utilize 1-hydroxy-2-naphthoic acid, o-phthalic acid, protoctechuic acid, gentisic acid or catechol. The oxidation of metabolic intermediates of phenanthrene by cells grown on phenanthrene, 2-hydroxy-1-naphthoic acid, salicylic acid or succinate as the sole carbon source was examined with a polarographic oxygen electrode.