Optimization of exopolysaccharide production and diesel oil emulsifying properties in root nodulating bacteria.

Bioremediation, a strategy mediated by microorganisms, is a promising way used in the degradation or removal of organic contaminants from soil or aquatic system. Exopolysaccharide (EPS) which was produced by a variety of Gram-negative bacteria has been demonstrated to be a potential bioemulsifier used in the degradation of hydrocarbons. In the present study, attempts were made to optimize the production of EPS from our newly isolates by adjusting the culture conditions and medium components. Besides, the performance of diesel oil emulsification using partially purified EPS derived from different conditions was also demonstrated. Out of 40 root nodulating bacteria the better emulsifying abilities were recorded from three strains namely Rhizobium miluonense CC-B-L1, Burkholderia seminalis CC-IDD2w and Ensifer adhaerens CC-GSB4, as can be seen from their emulsification index (E(24)) 66, 64 and 60%, respectively. These three strains produced 212, 203 and 198 mg l(-1) of EPS, respectively, in yeast extract mannitol (YEM) medium. After modifying culture conditions, better performances can be achieved from these three strains, with increases of 21.7, 21.4, 16.7% in the EPS production and 12.1, 10.9, 8.3% in E(24), respectively. When considered for strain CC-B-L1 and CC-IDD2w, the addition of 1.5% (v/v) of mannitol and 0.1% (v/v) of asparagine in YEM enhanced 42.9 and 34.7% in EPS production along with 28.8 and 37.5% higher in E(24). The supplement of 2.0% (v/v) glucose and 0.2% (v/v) asparagine in YEM increased 65.2% of EPS and 38.3% of E(24) in strain CC-GSB4. This is the first report demonstrating the optimization of diesel emulsification by EPS from root nodulating isolates, and these microbial agents might be used in the remediation of hydrocarbon contaminated soils in a near future.

Azospirillum picis sp. nov., isolated from discarded tar.

A polyphasic taxonomic study was performed on a pink-coloured unknown bacterium isolated from discarded road tar. Comparative analysis of the 16S rRNA gene sequence demonstrated that the isolate belongs phylogenetically to the genus Azospirillum with Azospirillum lipoferum, A. melinis and A. rugosum as its closest phylogenetic relatives (96.7, 96.6 and 96.6 % similarity to the respective type strains). The generic assignment was confirmed on the basis of chemotaxonomic data, which revealed a fatty acid profile characteristic for the genus Azospirillum, consisting of straight-chain saturated and unsaturated fatty acids, with C(18 : 1)omega7c as the major unsaturated non-hydroxylated fatty acid, and C(16 : 0) 3-OH as the major hydroxylated fatty acid, and a ubiquinone with ten isoprene units (Q-10) as the predominant respiratory quinone. On the basis of both the phenotypic and molecular genetic evidence, it is proposed that the unknown isolate should be classified within a novel species of the genus Azospirillum, for which the name Azospirillum picis sp. nov. is proposed. The type strain is IMMIB TAR-3(T) (=CCUG 55431(T) =DSM 19922(T)).

Sphingobium rhizovicinum sp. nov., isolated from rhizosphere soil of Fortunella hindsii (Champ. ex Benth.) Swingle.

The taxonomic status of a pale-yellow-coloured bacterial isolate from rhizosphere soil of Fortunella hindsii (Champ. ex Benth.) Swingle was characterized using a polyphasic taxonomic approach. Comparative analysis of the 16S rRNA gene sequence showed that the isolate constituted a distinct branch within the genus Sphingobium. The generic assignment was confirmed by chemotaxonomic data, which revealed the presence of a fatty acid profile that was characteristic for the genus Sphingobium, consisting of straight-chain saturated and unsaturated as well as 2-OH fatty acids and the lack of 3-OH fatty acids, ubiquinone with ten isoprene units (Q-10) as the predominant respiratory quinone, and a polar lipid pattern that consisted of the predominant compounds phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, diphosphatidylglycerol, sphingoglycolipid and an unknown glycolipid. Spermidine was the major polyamine component. The genotypic and phenotypic data (physiology and fatty acid and polar lipid profiles) showed that the isolate merits classification as representing a novel species of the genus Sphingobium, for which the name Sphingobium rhizovicinum sp. nov. is proposed. The type strain is CC-FH12-1T (=CCM 7491(T)=BCRC 17770T) [corrected]

Azospirillum rugosum sp. nov., isolated from oil-contaminated soil.

The taxonomic status of a light-orange-coloured bacterial isolate from an oil-contaminated soil sample was characterized by using a polyphasic taxonomic approach. Comparative analysis of 16S rRNA gene sequences demonstrated that the isolate belonged phylogenetically to the genus Azospirillum, with Azospirillum canadense, Azospirillum brasilense and Azospirillum doebereinerae as its closest phylogenetic relatives (97.3, 97.0 and 97.0 % similarity, respectively). DNA-DNA pairing studies showed that the unidentified organism displayed 25.0, 17.0 and 19.0 % relatedness to the type strains of A. brasilense, A. canadense and A. doebereinerae, respectively. The generic assignment was confirmed by chemotaxonomic data, which revealed a fatty acid profile that was characteristic of the genus Azospirillum, consisting of straight-chain saturated and unsaturated fatty acids with C18 : 1 omega 7c as the major fatty acid, and ubiquinone with ten isoprene units (Q-10) as the predominant respiratory quinone. On the basis of both the phenotypic and molecular genetic evidence, it is proposed that the unknown isolate be classified as a representative of a novel species of the genus Azospirillum, for which the name Azospirillum rugosum sp. nov. is proposed. The type strain is IMMIB AFH-6T (=CCUG 53966T=DSM 19657T).

Sphingobium olei sp. nov., isolated from oil-contaminated soil.

The taxonomic status of a yellow-coloured bacterial isolate from an oil-contaminated soil sample was determined using a polyphasic taxonomic approach. Comparative analysis of 16S rRNA gene sequences showed that the novel isolate formed a distinct phyletic line within the genus Sphingobium. The generic assignment was confirmed by chemotaxonomic data, which revealed: a fatty acid profile that is characteristic of the genus Sphingobium consisting of straight-chain saturated and unsaturated as well as 2-OH fatty acids; a ubiquinone with ten isoprene units (Q-10) as the predominant respiratory quinone; a polar lipid pattern consisting of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine and sphingoglycolipid, and spermidine as the major polyamine component. Genotypic and phenotypic data show that the new isolate merits classification as a representative of a novel species of the genus Sphingobium, for which the name Sphingobium olei sp. nov. is proposed. The type strain is IMMIB HF-1T (=DSM 18999T=CCUG 54329T).