Publications

4616

AbstractBACKGROUND: In the present investigation, the effect of Candidatus Liberibacter asiaticus (Las), a bacterium considered to be responsible for causing huanglongbing (HLB) disease in citrus, on the physiology of its vector, the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama, was determined. Specifically, the effects of Las infection on the susceptibility of ACP to selected insecticides were determined. Furthermore, total protein content and general esterase activity were quantified in Las‐infected and uninfected ACP to gain insight into the possible mechanism(s) responsible for altered susceptibility to insecticides owing to Las infection.RESULTS: LC50 values were significantly lower in Las‐infected than in uninfected ACP adults for chlorpyrifos and spinetoram. Furthermore, there was a general trend towards lower LC50 values for three other insecticides for Las‐infected ACP; however, the differences were not statistically significant. Total protein content (µg mL−1) was significantly lower in Las‐infected (23.5 ± 1.3 in head + thorax; 27.7 ± 1.9 in abdomen) than in uninfected (29.7 ± 2.1 in head + thorax; 35.0 ± 2.3 in abdomen) ACP. Likewise, general esterase enzyme activity (nmol min−1 mg−1 protein) was significantly lower in Las‐infected (111.6 ± 4.5 in head + thorax; 109.5 ± 3.7 in abdomen) than in uninfected (135.9 ± 7.5 in head + thorax; 206.1 ± 23.7 in abdomen) ACP.CONCLUSION: Susceptibility of ACP to selected insecticides from five major chemistries was greater in Las‐infected than in uninfected ACP. The lower total protein content and reduced general esterase activity in Las‐infected than in uninfected ACP may partly explain the observed higher insecticide susceptibility of Las‐infected ACP. Copyright © 2010 Society of Chemical Industry

Abstract Marine pelagic redoxclines are areas of enhanced biogeochemical cycling inhabited by distinct functional groups of prokaryotes. In this study, the diversity and abundance of archaeal and bacterial nitrifying populations throughout a pelagic redoxcline in the central Baltic Sea were examined using a suite of molecular methods. 16S rRNA/rRNA gene as well as bacterial and archaeal amoA mRNA/amoA gene fingerprints and clone libraries revealed that the putative nitrifying assemblages consisted solely of one crenarchaeotal subcluster, named GD2, which was closely related to Candidatus Nitrosopumilus maritimus. Neither distinct differences between transcript- and gene-based fingerprints nor pronounced differences in the crenarchaeotal composition throughout the whole redoxcline were detected. The abundance of this GD2 subgroup, as determined by the oligonucleotide probe Cren537 and the newly developed and more specific probe Cren679 showed that GD2 and total crenarchaeotal cell numbers were nearly identical throughout the redoxcline. The highest GD2 abundance (2.3 × 105 cells ml−1) occurred in the suboxic zone, accounting for around 26% of total prokaryotic cells. Below the chemocline, GD2 abundance was relatively stable (1.5–1.9 × 105 cells ml−1). Archaeal amoA expression was detected only in the putative nitrification zone and formed a narrow band in the suboxic layer, where ammonium, oxygen, nitrate, nitrite and phosphate concentrations were below 5 μmol l−1. To our knowledge this is the first study to show the dominance of only one crenarchaeotal nitrifying key cluster in a natural habitat. The metabolic properties and survival mechanisms present in this cluster inside and outside the nitrification zone remain to be determined.

A novel aerobic, heterotrophic bacterium, designated BiosLi39T, was isolated from the South East Pacific Ocean. Cells were Gram-negative gliding rods forming yellow colonies on marine agar. The isolate was oxidase-, catalase- and alkaline phosphatase-positive andβ-galactosidase-negative. Strain BiosLi39Tgrew at 20-37 °C (optimum 30 °C), at pH 7.0–9.0 (optimum pH 8.0) and with 20–60 g NaCl l−1(optimum 30–50 g NaCl l−1). The fatty acids (>1 %) comprised iso-C14 : 0, iso-C15 : 1G, iso-C15 : 0, anteiso-C15 : 0, C15 : 1G, C15 : 0, iso-C15 : 02-OH, iso-C16 : 1G, iso-C16 : 0, iso-C16 : 03-OH, iso-C16 : 02-OH, iso-C17 : 03-OH, C17 : 02-OH and three unidentified components with equivalent chain lengths of 17.87, 18.10 and 18.71. A significant proportion of the hydroxylated fatty acids are amide-linked. The lipid pattern indicated the presence of phosphatidylethanolamine, two unidentified aminolipids and three unidentified polar lipids. The strain contained menaquinone 7 as the sole respiratory lipoquinone and did not produce flexirubin-type pigments. The G+C content of the genomic DNA was 37.2 mol%. Comparative 16S rRNA gene sequence analysis indicated that strain BiosLi39Twas distantly related to all of the representatives of the phylumBacteroidetes. Its closest relative wasMarinoscillum furvescensIFO 15994T, with which it shared 92.5 % 16S rRNA gene sequence similarity. On the basis of genotypic, phenotypic and chemotaxonomic characteristics, we propose a novel genus and species,Ekhidnagen. nov., sp. nov., with type strain BiosLi39T(=DSM 19307T=CIP 109600T=OOB 398T).