Highly viscous polysaccharide produced by an Enterobacter isolate on a hemicellulose hydrolysate

Characterization, Phylogenetic Analyses, and Pathogenicity of Enterobacter cloacae on Rice Seedlings in Heilongjiang Province, China

Rice is used as a staple food in different areas of world, especially in China. In recent years, rice seedlings have been affected seriously by symptoms resembling bacterial palea browning (BPB) in Heilongjiang Province. To isolate and identify the pathogenic bacteria responsible for the disease, 40 bacterial strains were isolated from diseased rice seedlings collected from the four major accumulative-temperature zones of rice fields cultivated in Heilongjiang Province, and these were identified as 13 species based on morphological characteristics and 16S ribosomal RNA (rRNA) gene sequences. Inoculation of all the isolates on healthy rice seedlings showed that the nine Enterobacter cloacae isolates were the pathogens causing typical symptoms of BPB, including yellowing to pale browning, stunting, withering, drying, and death. Moreover, the nine E. cloacae isolates could also cause symptoms of bacterial disease on the seedlings of soybean (Glycine max), maize (Zea mays L.), and tomato (Solanum lycopersicum). Phylogenetic analysis based on the 16S rRNA gene sequences and phenotypic and biochemical characteristics indicated that these nine pathogenic isolates were E. cloacae. In addition, analysis of the sequences of four housekeeping genes (rpoB, gyrB, infB, and atpD) from the selected strain SD4L also assigned the strain to E. cloacae. Therefore, E. cloacae is the pathogen causing disease of rice seedlings in Heilongjiang Province, which we propose to classify as a form of BPB. To the best of our knowledge, this is the first study to identify E. cloacae as a causal agent of BPB in rice.

Association of Enterobacter cloacae with Rhizome Rot of Edible Ginger in Hawaii

Edible ginger is a popular spice crop that is grown in Hawaii primarily for the fresh market, and as such, rhizome quality is of paramount importance. In our studies, a Gram-negative, facultative anaerobic, rod-shaped bacterium was consistently isolated from decayed as well as symptomless ginger rhizomes. The bacterium was identified as Enterobacter cloacae by biochemical assays and 16S rDNA sequence analysis. Rot symptoms, which usually occurred in the central cylinder of the rhizome, were characterized by yellowish-brown to brown discolored tissue and firm to spongy texture. In inoculation experiments, ginger strains of E. cloacae produced basal stem and root rot, with foliar chlorosis and necrosis in tissue-cultured ginger plantlets, and discolored and spongy tissue in mature ginger rhizome slices and whole segments. In other hosts, ginger strains of E. cloacae caused internal yellowing of ripe papaya fruit and internal rot of onion bulbs. All strains that caused symptoms in inoculated plants were reisolated and identified as E. cloacae. Our studies suggest that E. cloacae can exist as an endophyte of ginger rhizomes, and under conditions that are favorable for bacterial growth, or host susceptibility, including maturity of tissues, rhizome rot may occur. Rhizome quality may be impacted by the presence of E. cloacae under conditions such as high temperature, high relative humidity, and low oxygen atmosphere that may affect the development of decay, and such conditions should be avoided during post-harvest handling and storage. The association of E. cloacae with a rhizome rot of ginger is a new finding.

Production and rheological properties of a succinoglycan from Pseudomonas sp. 31260 grown on wood hydrolysates

Pseudomonas sp. ATCC 31260 produced substantial amounts of anionic extracellular polysaccharide (EPS) from a mineral acid hydrolysate of wood, prepared using the "Tennessee Valley Authority" process. Partially purified EPS production approached 16.5 g/L (as hexadecyltrimethylammonium bromide precipitate) when the pH of the hydrolysate was initially adjusted to 7.5 and amended with 0.05% each of peptone and yeast extract. This EPS, now characterized as a succinoglycan, is composed of glucose, galactose, succinate, pyruvate, and acetate. Solutions of this EPS are pseudoplastic, and under specified conditions, are rheologically comparable with commercially available xanthan.

Optimization of Novel Extracellular Polysaccharide Production by an Enterobacter sp, on Wood Hydrolysates

An environmental isolate identified as Enterobacter cloacae has been found to produce a highly viscous, anionic extracellular polysaccharide (EPS) from a weak mineral acid hydrolysate of hardwood. Production of this EPS has been optimized on the hydrolysate (initial pH, 6.3; NH 4 Cl amendment, 0.1%) so that crude yields approaching 9.83 g/liter were obtained. Although this EPS is polydisperse, its molecular mass as determined by gel exclusion chromatography centers at approximately 1,700 kDa. Solutions of this EPS have been examined rheologically under a variety of conditions and compare favorably with both xanthan and alginate.