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Genetic and functional diversity of Citrobacter spp. for their abilities to degrade aromatic compounds was evaluated to develop mixed cultures or a consortium for bioremediation technology. Thirty Citrobacter strains isolated from various effluent treatment plants were found to degrade a range of aromatic compounds: phenol, benzoate, hydroxy benzoic acid and biotransform mono-chlorophenols and di-chlorophenol within 24 to 48 h of incubation at 30 °C. Sequence similarity and phylogeny of the ARHD gene transcripts (730 nucleotides) depicted their diversity within 9 Citrobacter strains: HPC255, HPC369, HPC560, HPC570, HPC784, HPC1196, HPC1216, HPC1276 and HPC1299. Here, the degree of associations varied up to 84% with (i) ARHD α-sub unit (SU), (ii) LSU of Phenylpropionate dioxygenase (PDO), (iii) Phenol hydroxylase α-SU, (iv) Benzoate 1,2-dioxygenase, α-SU, (v) Naphthalene dioxygenase LSU, etc. This study has provided basic information, which can be used to develop a consortium of bacteria with mutually beneficial characteristics.

A scheme for microbial production of 2,3-butanediol from water hyacinth (WH), a nuisance weed, is presented. It consists in sun-drying WH followed by crushing, alkaline treatment at high temperature, enzymatic hydrolysis, and fermentation. A caustic soda concentration of 1% and steam pressure of 1 kg/cm 2 for 1 h were optimal for delignification and yielded 35 g delignified water hyacinth (DLWH)/100 g crude water hyacinth. A slurry concentration of 5%, an enzyme concentration yielding filter-paper cellulase activity (FPCA) of 14 IU/g DLWH, a temperature of 50°C, a pH of 4·8, and an incubation period of 48 h were optimal for enzymatic hydrolysis yielding 19 g/litre reducing sugars. Prefermentation hydrolysis followed by combined hydrolysis and fermentation (PH-CHF) was most efficient and yielded 15 g 2,3-butanediol per 100 g DLWH. An HRT of 4 h corresponding to a productivity of 1·4 g/litre/h of 2,3-butanediol with anaerobic-fixed-film and upflowanaerobic-sludge-blanket (UASB) reactor systems was achieved on WH hydrolysate in a continuous mode.

A strain, Stenotrophomonas HPC383 is isolated from effluent treatment plant treating wastewater from pesticide industry; degrades various aromatic compounds (cresols, phenol, catechol, 4methyl-catechol and hydroquinone) and crude oil, as determined through HPLC and GC analysis. Culture HPC383 could degrade (%) various compounds (1 mM) from a mixture: phenol - 99, p-cresol - 100, 4-methylcatechol - 96 and hydroquinone - 43 within 48 h of incubation, whereas it took 7 days to degrade 94% of 0.5% crude oil. Gene locus dmpN, to identify phenol degrading capacity was determined by PCR followed by southern analysis. The sequenced DNA fragment exhibited 99% sequence similarity to phenol hydroxylase gene from Arthrobacter sp. W1 (FJ610336). Amino acid sequence analysis of phenol hydroxylase reveals it to belong to high-Ks (affinity constant) group. Application of HPC383 in bioremediation of aquatic and terrestrial sites contaminated with petrochemical has been suggested.

In this study, the samples were collected from nine ETPs and soil contaminated with petroleum products. The genetic diversity of 30 Stenotrophomonas isolates was demonstrated by phylogenetic analysis of their 16S rRNA gene nucleotide sequences, and randomly amplified polymorphic DNA (RAPD) analysis supplemented with in silico signature and restriction enzyme (REs--AluI, BfaI, DpnII, HaeIII, RsaI and Tru9I) digestion analyses. Genetic diversity based on nucleotide sequence data revealed distinct clusters. Functional diversity was analysed on the basis of the abilities of these isolates to degrade phenol, p-cresol, catechol, 4-methylcatechol and hydroquinone. Based on the environmental, genetic and functional diversities, a consortium of mixed defined microbes has been proposed for bioremediation programs.