Diversity and Distribution of Culturable Thermus Species in Terrestrial Hot Springs of Southwestern Yunnan Province in China

The Yunnan geothermal area has many neutral and alkalescent thermal springs. Members of the genus Thermus have been found in thermal environments. In this study, we attempted to cultivate numerically abundant Thermus species using a variety of different strategies. A total of 223 strains of Thermus-like bacteria were isolated from seventeen hot spring samples of four geothermal regions (Baoshan, Dali, Lincang and Dehong). These strains were classified into two genera, Thermus and Meiothermus, based on 16S rDNA. The optimal isolation temperature of the Thermus genus was 63–70 °C. The highest Thermus diversity was found at 63 °C. Thermus brockianus was a universal culturable bacterium in the four geothermal regions. The principal component analysis (PCA) showed that T. oshimai preferred to inhabit the hot springs of the Baoshan (Bs) geothermal region, and T. amyloliquefaciens dominated the Dali (Dl) geothermal region, whereas T. tengchongensis accumulated in the Lincang (Lc) and Dehong (Dh) geothermal regions. The results suggested that Thermus species had habitat-preferable characteristics among the four geothermal regions. The findings may help identify the niche from which Thermus strains can likely be isolated.

Early Population Dynamics of “Candidatus Liberibacter asiaticus” in Susceptible and Resistant Genotypes After Inoculation With Infected Diaphorina citri Feeding on Young Shoots

Huanglongbing is a highly destructive citrus disease associated with “Candidatus Liberibacter asiaticus” (Las), a phloem−limited and non-culturable bacterium, naturally transmitted by the psyllid Diaphorina citri. Although diverse approaches have been used to understand the molecular mechanisms involved in the pathogen–host interaction, such approaches have focused on already infected and/or symptomatic plants, missing early events in the initial days post-inoculation. This study aimed to identify the time course of Las multiplication and whole-plant colonization immediately following inoculation by infected psyllids feeding for 2 days. Thus, the experimental approach was to track Las titers after psyllid inoculation in new shoots (NS) of Citrus × sinensis (susceptible), Murraya paniculata (partially resistant), and Bergera koenigii (fully resistant). Soon after psyllid removal, Las titers dropped until the 10–12th days in all three species. Following this, Las titers increased exponentially only in C. × sinensis and M. paniculata, indicating active bacterial multiplication. In C. × sinensis, Las reached a stationary phase at ∼5 log Las cells/g of tissue from the 40th day onward, while in M. paniculata, Las increased at a lower rate of up to ∼3 log Las cells/g of tissue between the 40th and 60th days, decreasing gradually thereafter and becoming undetectable from the 160th day onward. In B. koenigii, Las titers decreased from the start and remained undetectable. In C. × sinensis, an average of 2.6 log of Las cells/g of tissue was necessary for Las to move out of 50% of the NS in 23.6 days and to colonize the rest of the plant, causing a successful infection. Conversely, the probability of Las moving out of the NS remained below 50% in M. paniculata and zero in B. koenigii. To our knowledge, this is the first study on Las dynamics and whole-plant colonization during the earliest stages of infection. Identification of critical time-points for either successful multiplication or Las resistance may help to elucidate initial events of Las–host interactions that may be missed due to longer sampling intervals and at later stages of infection.

Two Peptides, Cycloaspeptide A and Nazumamide A from a Sponge Associated Marine Actinobacterium Salinispora sp

Marine sponges are a major component of benthic communities and act as a reservoir for microbial species. In terms of biomass, they are the richest source of secondary metabolite production, with the potential to influence both benthic and pelagic systems. In most cases it is the sponge-associated microbes that account for many of the secondary metabolites assigned to the host. Here we report the occurrence of cycloaspeptide A, a fungus-derived cyclic peptide, in a culturable bacterium Salinispora arenicola. We have also identified nazumamide A, a sponge-derived linear tetrapeptide currently used as a thrombin inhibitor, in Salinispora pacifica. Their structures were determined using an integrated approach consisting of: (1) HPLC-UV-Vis-QToF-MS analysis with multimode ionization (ESI and APCI) and fast polarity switching; (2) database searching and matching of monoisotopic masses, retention times, mass spectra of the precursor and product ions of the compounds of interest and the authentic reference standards thereof.

Symbiosis of Aeromonas veronii Biovar sobria and Hirudo medicinalis, the Medicinal Leech: a Novel Model for Digestive Tract Associations

ABSTRACT Hirudo medicinalis, the medicinal leech, is applied postoperatively in modern medicine. Infections by Aeromonasoccur in up to 20% of patients unless a preemptive antibiotic treatment is administered. The associated infections demonstrate the need for a better understanding of the digestive tract flora ofH. medicinalis. Early studies reported the presence of a single bacterial species in the digestive tract and suggested that these bacteria were endosymbionts contributing to the digestion of blood. In this study, we cultivated bacteria from the digestive tract and characterized them biochemically. The biochemical test results identified the isolates as Aeromonas veronii biovar sobria. This species identification was supported by sequence comparison of a variable region of the genes coding for 16S rRNA. In a colonization assay, a rifampin-resistant derivative of a symbiotic isolate was fed in a blood meal to H. medicinalis. The strain colonized the digestive tract rapidly and reached a concentration similar to that of the native bacterial flora. For the first 12 h, the in vivo doubling time was 1.2 h at 23°C. After 12 h, at a density of 5 × 107 CFU/ml, the increase in viable counts ceased, suggesting a dramatic reduction in the bacterial growth rate. Two human fecal isolates, identified as Aeromonas hydrophila and A. veronii biovar sobria, were also able to colonize the digestive tract. These data demonstrate that the main culturable bacterium in the crop of H. medicinalis isA. veronii biovar sobria and that the medicinal leech can be used as a model for digestive tract association ofAeromonas species.