Baoping Liu

Antibacterial activity of two chitosan solutions and their effect on rice bacterial leaf blight and leaf streak

BACKGROUND Bacterial leaf blight and leaf streak are the two most damaging bacterial diseases of rice. However, few bactericidal chemicals are available for controlling both diseases. The antibacterial properties of two kinds of chitosan with different molecular weights and degrees of N-deacetylation and their effect on rice bacterial leaf blight and leaf streak were evaluated. RESULTS Results showed that the two kinds of chitosan solution possess a strong antibacterial activity against both rice bacterial pathogens and significantly reduced disease incidence and severity by comparison with the control under greenhouse conditions. However, the interaction between chitosan and rice pathogens was affected by the type and concentration of chitosan, the bacterial species and the contact time between chitosan and bacteria. The direct antibacterial activity of chitosan may be attributed to both membrane lysis and the destruction of biofilm. In addition, both chitosan solutions significantly increased the activities of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase in rice seedlings following inoculation of two rice pathogens by comparison with the control. CONCLUSION The role of chitosan in protection of rice against bacterial pathogens has been shown to involve direct antibacterial activity and indirect induced resistance.

Effect of Chitosan Solution on the Inhibition of Pseudomonas fluorescens Causing Bacterial Head Rot of Broccoli

The in vitro antibacterial properties of two kinds of chitosan solutions and their effect in protection of broccoli from bacterial head rot disease were evaluated. Results showed that the two kinds of chitosan solution at different concentrations exhibited strong antibacterial activity against Pseudomonas fluorescens. However, the antibacterial activity of chitosan A solution increased with the increase of chitosan concentration up to 0.10 mg/ml while the antibacterial activity of chitosan B solution increased with the increase of chitosan concentration up to 0.05 mg/ml. In addition, the antibacterial activity of chitosan A and chitosan B solution of 0.10 mg/ml increased with the incubation time within 12 h and 24 h, respectively. The disease incidence and the lesion diameter of broccoli inoculated with P. fluorescens were significantly reduced when plants were either pretreated or post-treated with six different combinations of chitosan solutions. Overall, the results indicated that the two kinds of chitosan solutions had a potential in controlling bacterial head rot of broccoli.

Bacterial brown stripe of rice in soil-less culture system caused by Acidovorax avenae subsp. avenae in China

In 2010, the outbreak of a disease with symptoms similar to bacterial brown stripe was observed in rice seedlings planted in a perlite culture system in China. The causal bacterium was identified as Acidovorax avenae subsp. avenae based on its biochemical and physiological characteristics, cellular fatty acid composition, Biolog data, specific PCR detection and 16S rRNA gene sequence analysis. The bacterial isolates caused similar symptoms after inoculation of rice seedlings. This report is the first of bacterial brown stripe of rice in a soil-less culture system caused by A. avenae subsp. avenae in China.

Differentiation in MALDI-TOF MS and FTIR spectra between two closely related species Acidovorax oryzae and Acidovorax citrulli

BackgroundTwo important plant pathogenic bacteria Acidovorax oryzae and Acidovorax citrulli are closely related and often not easy to be differentiated from each other, which often resulted in a false identification between them based on traditional methods such as carbon source utilization profile, fatty acid methyl esters, and ELISA detection tests. MALDI-TOF MS and Fourier transform infrared (FTIR) spectra have recently been successfully applied in bacterial identification and classification, which provide an alternate method for differentiating the two species.ResultsCharacterization and comparison of the 10 A. oryzae strains and 10 A. citrulli strains were performed based on traditional bacteriological methods, MALDI-TOF MS, and FTIR spectroscopy. Our results showed that the identity of the two closely related plant pathogenic bacteria A. oryzae and A. citrulli was able to be confirmed by both pathogenicity tests and species-specific PCR, but the two species were difficult to be differentiated based on Biolog and FAME profile as well as 16 S rRNA sequence analysis. However, there were significant differences in MALDI-TOF MS and FTIR spectra between the two species of Acidovorax. MALDI-TOF MS revealed that 22 and 18 peaks were specific to A. oryzae and A. citrulli, respectively, while FTIR spectra of the two species of Acidovorax have the specific peaks at 1738, 1311, 1128, 1078, 989 cm-1 and at 1337, 968, 933, 916, 786 cm-1, respectively.ConclusionsThis study indicated that MALDI-TOF MS and FTIR spectra may give a new strategy for rapid bacterial identification and differentiation of the two closely related species of Acidovorax.

Synthesis, characterization, and antibacterial activity of chitosan/TiO2 nanocomposite against Xanthomonas oryzae pv. oryzae.

This present study deals with synthesis, characterization and antibacterial activity of chitosan/TiO2 nanocomposites. Results indicated that chitosan/TiO2 nanocomposite at the ratio of 1:5 showed the strongest inhibition in growth of rice bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo). Furthermore, the antibacterial activity of chitosan/TiO2 nanocomposite against Xoo is significantly higher than that of the two individual components under both light and dark conditions. Regardless of the presence or absence of extracellular polymeric substances, chitosan/TiO2 nanocomposite showed strong antibacterial activity, however, the absence increased the sensitivity of Xoo to chitosan/TiO2 nanocomposite. In addition, the surface morphology and physicochemical properties of chitosan/TiO2 nanocomposite is different from the two individual components based on scanning electron microscopic observation, fourier transform infrared spectra, and X-ray diffraction pattern, as well as elemental and thermo gravimetric analysis. Overall, this study indicated that this synthesized chitosan/TiO2 nanocomposite is promising to be developed as a new antibacterial material.

Characterization and comparison of Serratia marcescens isolated from edible cactus and from silkworm for virulence potential and chitosan susceptibility

Representative strains of Serratia marcescens from an edible cactus plant and silkworms were characterized and a comparison based on their cellular fatty acid composition, 16S rRNA and groE gene sequence analysis as well as silkworm virulence and chitosan susceptibility was carried out. Results from this study indicate that there are no significant differences between the phenotypic and molecular characterization, virulence and chitosan susceptibility of the S. marcescens strains from the cactus plant and silkworms. Silkworms inoculated with S. marcescens from either plant or silkworm resulted in nearly 100% mortality. Chitosan solution exhibited strong antibacterial activity against S. marcescens. This activity increased with the increase of chitosan concentration and incubation time regardless of the strain source. Also, the results indicate that the plant associated S. marcescens maybe plays a possible role in the contamination of humans and animals, in particular silkworms, while chitosan showed a potential to control the contamination caused by S. marcescens.

Bacterial wilt of mulberry (Morus alba) caused by Enterobacter cloacae in China.

In August of 2006, a new bacterial disease was noted in Hangzhou mulberry orchards of Zhejiang Province, China where bacterial wilt of mulberry caused by Ralstonia solanacearum was previously reported (3). In the summer, the disease caused severe wilt, especially on 1- or 2-year-old mulberry plants, that resulted in premature plant death. Leaf wilt symptoms generally started on older leaves at the bottom of the plant and spread to the younger leaves. The leaves of infected plants became withered and dry, turned dark brown, and eventually the plants became defoliated. The root xylem of infected plants was moist and discolored with brown stripes. The phloem was asymptomatic, however, in severe infections, the phloem was decayed. The observation of wilting proceeding from the bottom of the plant to the top distinguishes this disease from bacterial wilt caused by R. solanacearum. Five bacterial strains isolated from infected mulberry plants showed characteristics similar to those of the standard reference strain of Enterobacter cloacae subsp. cloacae IBJ0611from China, but differed from R. solanacearum IBJ35, E. cancerogenus LMG2693T, and E. cloacae subsp. dissolvens LMG2683T from the University of Gent, Belgium in phenotypic tests, including the Biolog Identification System version 4.2 (Biolog Inc., Hayward CA), pathogenicity tests, transmission electron microscopy (TEM,KYKY-1000B, Japan) observation, and gas chromatographic analysis of fatty acid methyl esters (FAMEs) using the Microbial Identification System (MIDI Company, Newark, DE) with the aerobic bacterial library (TABA50). Isolates were gram negative, facultative anaerobic, rod shaped, 0.3 to 1.0 × 1.0 to 3.0 μm with peritrichous flagella. Colonies on nutrient agar were light yellow, smooth, circular, entire, and convex with no green fluorescent diffusible pigment on Kings medium B (3). Weak hypersensitive reaction was observed on tobacco 3 days after inoculation. All five strains were identified as E. cloacae with Biolog similarity of 0.662 to 0.863 and FAMEs similarity of 0.632 to 0.701. Inoculation of 10 6-month-old intact mulberry plants of cv Husang with cell suspensions containing 109 CFU/ml by pinprick at the base of the stem reproduced symptoms observed in natural infections. No symptoms were noted on the two control plants inoculated by the same method but with sterilized distilled water. The bacterium was reisolated from the symptomatic mulberry plants. E. cloacae has been reported from the United States as the cause of internal yellowing of papaya fruits (1) and rhizome rot of edible ginger (2). To our knowledge, this is the first report of mulberry wilt caused by E. cloacae in China. References: (1) K. Nishijima et al. Plant Dis. 71:1029, 1987. (2) K. Nishijima et al. Plant Dis. 88:1318, 2004. (3) L. Xu et al. Acta Phytophylacica. Sin. 34:141, 2007.

Bacterial Fruit Rot of Apricot Caused by Burkholderia cepacia in China

An unreported disease of apricot was observed in orchards in Zhejiang province, China. Symptoms started as water soaked lesions on the fruit surface. Later, water-soaked areas developed and spread to the entire fruit, resulting in soft rot of the whole fruit. The causal organism isolated from symptomatic fruits was identified as Burkholderia cepacia based on its biochemical and physiological characteristics and confirmed by the cellular fatty acid composition and Biolog data as well as 16S rRNA gene sequence analysis. The bacterial isolates caused similar symptoms when inoculated onto fruits of apricot. In addition, European plum, Japanese plum, nectarine and kiwifruit were susceptible to the B. cepacia pathogen. However, the B. cepacia pathogen failed to cause any visible symptoms when it was inoculated onto 16 other fruits. This is the first report of a bacterial disease of apricot caused by B. cepacia in China.