Pontixanthobacter rizhaonensis sp. nov., a marine bacterium isolated from surface seawater of the Yellow Sea, and proposal of Pseudopontixanthobacter gen. nov., Pseudopontixanthobacter confluentis comb. nov. and Pseudopontixanthobacter sediminis comb. nov.

A bacterial strain designated RZ02T was isolated from surface seawater collected from the Yellow Sea in PR China and characterized by polyphasic taxonomy. Cells of strain RZ02T were Gram-stain-negative, aerobic, non-motile, catalase- and oxidase-positive rods forming ochre-pigmented colonies. Growth occurred at 7-36 °C (optimum, 30 °C), at pH 6.0-9.0 (optimum, pH 7.0) and with 1-5 % (optimum, 2 %) NaCl. The major cellular fatty acids (>10 %) of strain RZ02T were summed feature 8 (C18 : 1 ω6c and/or C18 : 1 ω7c), summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and C16 : 0. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol and sphingoglycolipid. The genome size of strain RZ02T was 2.79 Mbp with a G+C content of 55.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain RZ02T was mostly related to Pontixanthobacter luteolus SW-109T and Pontixanthobacter aestiaquae HDW-31T (97.3 and 97.1% sequence similarity, respectively), and formed a phyletic lineage with members of the genus Pontixanthobacter. The phylogenetic analysis based on the up-to-date bacterial core gene sequences confirmed that strain RZ02T clustered within the genus Pontixanthobacter. The average nucleotide identity and in silico DNA-DNA hybridization values between strain RZ02T and P. luteolus SW-109T and P. aestiaquae HDW-31T were 72.8 and 72.9 % and 18.7 and 18.5%, respectively. Based on these evidences, strain RZ02T is proposed to represent a novel species of the genus Pontixanthobacter under the name Pontixanthobacter rizhaonensis sp. nov. The type strain is RZ02T (=KCTC 62828T=MCCC 1K04521T). In addition, based on the results of whole genome analyses, proposals of Pseudopontixanthobacter gen. nov., Pseudopontixanthobacter confluentis comb. nov. and Pseudopontixanthobacter sediminis comb. nov. are also included.

[Experimental study on cross-resistance of Culex pipiens pallens to 3 kinds of chemical pesticides].

OBJECTIVE: To understand the cross-resistance of Culex pipiens pallens to common pesticides, so as to provide the evidence for improving the application of chemical pesticides. METHODS: The IV instar larvae of DDVP-resistant, propoxur-resistant and cypermethrin-resistant strains as well as the sensitive strain of Culex pipiens pallens were collected to detect the resistance to DDVP, propoxur and cypermethrin based on the WHO bioassay method. RESULTS: The resistance coefficients of DDVP-resistant strain to DDVP, propoxur and cypermethrin were 14.47, 8.96 and 207.27 respectively. The resistance coefficients of propoxur-resistant strain to DDVP, propoxur and cypermethrin were 3.27, 6.93 and 8.65 respectively. The resistance coefficients of cypermethrin-resistant strain to DDVP, propoxur and cypermethrin were 2.93, 1.61 and 501.11 respectively. CONCLUSION: The resistance and cross-resistance could be generated during the long-term application of a single kind of chemical pesticide, and we should pay more attention to the varieties and dosages of them.

[Differences of acetylcholinesterase level in variety classes and strains of Culex pipiens pallens].

OBJECTIVE: To investigate the diversity of acetylcholinesterase (AChE) activity in variety classes and strains of Culex pipiens pallens and provide a basis for the insecticide-resistance detection of mosquito by biochemical method. METHODS: AChE insensitivity of single mosquito was determined, using acetythiocholine iodide (ATch) as the substrate, 5,5'-dithio-bis (2-nitrobenzoic acid) (DTNB) as the developer, and propoxur as the inhibitor. RESULT: There were significant differences in AChE activity among the four types of IV instar larvae and 3-day-old adult female of sensitive strain mosquito (P<0.01). The AChE activity of the 3-day-old adult female was higher than that of IV instar larvae of the four types of sensitive strain mosquito (P<0.01). The AChE activity of anti-DDVP (Rd) and anti-propoxur (Rp) strains of Culex pipiens pallens was significantly higher than that of sensitive (S) strain (P<0.01), while the AChE activity of anti-cypermethrin (Rc) strain of Culex pipiens pallens was similar to that of S strain (P>0.05). The individual frequency of insensitive AChE of Rd and Rp strains of Culex pipiens pallens was significantly higher than that of sensitive (S) strain (P<0.01), while the individual frequency of insensitive AChE of Rc strain of Culex pipiens pallens was similar to that of S strain(P>0.05). CONCLUSION: The AChE activity determination can be used to examine the insecticide-resistance of mosquito.

[Drug resistance evolution of dichlorvos-resistant and cypermethrin-resistant strains of Culex pipiens pallens].

Susceptible strain of Culex pipiens pallens was selected with dichlorvos and cypermethrin for 42 generations in the laboratory. At generation 42, the resistance level to dichlorvos and cypermethrin was 12.2-fold and 534.3-fold, respectively, in comparison to their parent generations. The dichlorvos-resistant and cypermethrin-resistant strains were then conventionally bred for another 20 generations, the resistance level to dichlorvos and cypermethrin decreased to 6.1-fold and 83.3-fold, respectively. The results indicated that the two resistant strains showed different development of resistance.