Structure-function studies of the Vitreoscilla hemoglobin D-region

The D-region connecting helices C and E of Vitreoscilla hemoglobin (VHb) appears disordered in the crystal structure. Six site-directed mutants in this region were made to investigate its possible functions. The mutant VHb's were analyzed using UV-visible and FTIR spectroscopy, using primarily the CO liganded forms, and their heme/protein ratios were determined. The results implicate Asp44, Arg47, and Glu49 as especially important in heme-globin interactions and ligand binding, and enabled construction of a model in which the D-region forms a loop that protrudes upward over the heme. Interactions between VHb (wild type and the D-region mutants) with the flavin domain of 2,4-DNT dioxygenase from Burkholderia were tested using bacterial two-hybrid screening. There was a correlation between the extent of the D-loop perturbation predicted for each mutant and the amount of the reduction in VHb-flavin domain interaction, suggesting that this region may be more generally involved in binding of VHb to flavoproteins.     

Effects of host plant environment and Ustilago maydis infection on the fungal endophyte community of maize (Zea mays)

The focus of many fungal endophyte studies has been how plants benefit from endophyte infection. Few studies have investigated the role of the host plant as an environment in shaping endophyte community diversity and composition. The effects that different attributes of the host plant, that is, host genetic variation, host variation in resistance to the fungal pathogen Ustilago maydis and U. maydis infection, have on the fungal endophyte communities in maize (Zea mays) was examined. The internal transcribed spacer (ITS) region of the rDNA was sequenced to identify fungi and the endophyte communities were compared in six maize lines that varied in their resistance to U. maydis. It was found that host genetic variation, as determined by maize line, had significant effects on species richness, while the interactions between line and U. maydis infection and line and field plot had significant effects on endophyte community composition. However, the effects of maize line were not dependent on whether lines were resistant or susceptible to U. maydis. Almost 3000 clones obtained from 58 plants were sequenced to characterize the maize endophyte community. These results suggest that the endophyte community is shaped by complex interactions and factors, such as inoculum pool and microclimate, may be important.     

Identification and characterization of bacterial endophytes of rice

We isolated seven different bacteria from rice seedlings grown from surface sterilized seeds. Three were associated with the rice seed husk and the other four were growing endophytically within the seed. Microscopic studies revealed that the endophytes were concentrated in the root stele region. Some of the bacteria exhibited strong anti-fungal activity against Rhizoctonia solani, Pythium myriotylum, Guamannomyces graminis and Heterobasidium annosum.     

The facilitation of social interactions by domestic dogs

Abstract

Research suggests that dogs can facilitate social interactions, which, in turn, may promote psychological health. This study explored the ability of dogs to facilitate social responses relative to other accompaniments and investigated whether the social catalysis effect is generic or influenced by the appearance of the dog. The behavior of 1800 pedestrians approaching a female experimenter was recorded as a function of the presence of three dogs (Labrador Retriever pup, Labrador adult, Rottweiler adult) and two neutral stimuli (teddy bear, potted plant). The behavior of pedestrians approaching the woman whenever she was alone (control) was also explored. Information was collected on the passers-by’ gender, number of people in the party, type of acknowledgement elicited and length of conversations. More people ignored the experimenter whenever she was alone or with the teddy or plant, than whenever she was walking a dog. The Rottweiler resulted in more nonresponses than the puppy or adult Labrador, who in turn elicited more smiles and verbal responses. Females, and those alone, elicited more smiles and conversations than males, or those in pairs. It is concluded that dogs can facilitate social interactions between adults better than other accompaniments; however, the social catalysis effect is not generic, but dog specific.     

Lytic Activity of the Vibrio cholerae Type VI Secretion Toxin VgrG-3 Is Inhibited by the Antitoxin TsaB

The type VI secretion system (T6SS) of Gram-negative bacteria has been implicated in microbial competition; however, which components serve purely structural roles, and which serve as toxic effectors remains unresolved. Here, we present evidence that VgrG-3 of the Vibrio cholerae T6SS has both structural and toxin activity. Specifically, we demonstrate that the C-terminal extension of VgrG-3 acts to degrade peptidoglycan and hypothesize that this assists in the delivery of accessory T6SS toxins of V. cholerae. To avoid self-intoxication, V. cholerae expresses an anti-toxin encoded immediately downstream of vgrG-3 that inhibits VgrG-3-mediated lysis through direct interaction.     

Hydrolases on silica surfaces: Coverage-activity–molecular property relationships revealed

A set of recommendations to maintain high activity of immobilized enzymes is developed based on direct observation via AFM. This helps to close knowledge gaps that often lead to poor performance of nanobiocatalysts for chemical synthesis. Molecule-level height and volume distribution analyses from high-resolution AFM images were applied to Candida antarctica Lipase B (CALB), subtilisin Carlsberg, and the Lipase from Thermomyces lanuginosus (TLL) deposited on model silica surfaces. Ensembles of flexible or “soft” enzymes appear separated when interactions with the surface are considerable at low surface coverage but form highly entangled structures of increased conformational stability at high surface coverage. By contrast, ensembles of rigid or “hard” enzymes appear to maintain stable aggregates even under strong interaction with the surface. The more rigid the enzyme the higher its tendency to remain in a densely packed state that is able to withstand surface-induced conformational transitions detrimental to catalysis. Weakening of surface-protein interactions for “soft” enzymes will prevent single-molecule immobilization, which reduces catalytic competency through structural changes. Multi-layer coverage in enzyme immobilization should generally be avoided due to mass transfer limitations.