Yeasts from sub-Antarctic region: biodiversity,enzymatic activities and their potential as oleaginous microorganisms

Various microbial groups are well known to produce a range of extracellular enzymes and other secondary metabolites. However, the occurrence and importance of investment in such activities have received relatively limited attention in studies of Antarctic soil microbiota. Sixty-one yeasts strains were isolated from King George Island, Antarctica which were characterized physiologically and identified at the molecular level using the D1/D2 region of rDNA. Fifty-eight yeasts (belonging to the genera Cryptococcus, Leucosporidiella, Rhodotorula, Guehomyces, Candida, Metschnikowia and Debaryomyces) were screened for extracellular amylolytic, proteolytic, esterasic, pectinolytic, inulolytic xylanolytic and cellulolytic activities at low and moderate temperatures. Esterase activity was the most common enzymatic activity expressed by the yeast isolates regardless the assay temperature and inulinase was the second most common enzymatic activity. No cellulolytic activity was detected. One yeast identified as Guehomyces pullulans (8E) showed significant activity across six of seven enzymes types tested. Twenty-eight yeast isolates were classified as oleaginous, being the isolate 8E the strain that accumulated the highest levels of saponifiable lipids (42 %).     

Functional role of bacterial multidrug efflux pumps in microbial natural ecosystems

Multidrug efflux pumps have emerged as relevant elements in the intrinsic and acquired antibiotic resistance of bacterial pathogens. In contrast with other antibiotic resistance genes that have been obtained by virulent bacteria through horizontal gene transfer, genes coding for multidrug efflux pumps are present in the chromosomes of all living organisms. In addition, these genes are highly conserved (all members of the same species contain the same efflux pumps) and their expression is tightly regulated. Together, these characteristics suggest that the main function of these systems is not resisting the antibiotics used in therapy and that they should have other roles relevant to the behavior of bacteria in their natural ecosystems. Among the potential roles, it has been demonstrated that efflux pumps are important for processes of detoxification of intracellular metabolites, bacterial virulence in both animal and plant hosts, cell homeostasis and intercellular signal trafficking.     

The bacteriophage phi 29 DNA polymerase, a proofreading enzyme.

The bacteriophage phi 29 DNA polymerase, involved both in the protein-primed initiation and elongation steps of the viral DNA replication, displays a very processive 3',5'-exonuclease activity acting preferentially on single-stranded DNA. This exonucleolytic activity showed a marked preference for excision of a mismatched versus a correctly paired 3' terminus. These characteristics enable the phi 29 DNA polymerase to act as a proofreading enzyme. A comparative analysis of the wild-type phi 29 DNA polymerase and a mutant lacking 3',5'-exonuclease activity indicated that a productive coupling between the exonuclease and polymerase activities is necessary to prevent fixation of polymerization errors. Based on these data, the phi 29 DNA polymerase, a model enzyme for protein-primed DNA replication, appears to share the same mechanism for the editing function as that first proposed for T4 DNA polymerase and Escherichia coli DNA polymerase I on the basis of functional and structural studies.     

Pollen limitation may be a common Allee effect in marine hydrophilous plants: implications for decline and recovery in seagrasses

Oecologia - Pollen limitation may be an important factor in accelerated decline of sparse or fragmented populations. Little is known whether hydrophilous plants (pollen transport by water) suffer...     

Aureobasidium pullulans as a biocontrol agent of postharvest pathogens of apples in Uruguay

Aureobasidium pullulans was the microorganism most frequently recovered from the surface of apple fruit (cv. Red Delicious) stored in commercial cold chambers for 6 months. In the present work, 10 isolates of Aureobasidium pullulans were assayed to determine if they could control blue and grey mold disease of apple during cold storage. Although nine of 10 isolates, significantly reduced the percentage of decayed wounds when compared to the control, one of them, designated isolate ApB, showed the highest levels of protection. ApB was able to grow in a wide range of temperatures lower than 35°C, which is an important human health safety factor. ApB was resistant to thiabendazole, iprodione and imazalil, the most commonly commercially applied fungicides in postharvest treatment of apples in Uruguay. Regarding the mechanisms of action of the selected biocontrol agent, lytic enzymes did not seem to play a central role. ApB depleted iron from nutrient media, which may be an important aspect of its ability to inhibit Botrytis cinerea. Further experiments are needed, however, to determine if the depletion of iron is caused by the production of siderophores, by the immobilization of iron in an insoluble pigment, or a combination of both.     

Function and distribution of EspG2, a type III secretion system effector of enteropathogenic Escherichia coli

The enteropathogenic Escherichia coli (EPEC) effector protein EspG, like the Shigella effector VirA, functions through disruption of the host cell microtubule network. Reports have differed as to whether the EspG homologue, EspG2, is also responsible for microtubule disruption. In this study we show that following translocation, EspG2 and VirA are localised under adherent bacteria and able to restore the microtubule disruption phenotype to an espG/espG2 double EPEC mutant. The espG/espG2 double mutant produced A/E lesions similar to wild-type EPEC on human intestinal in vitro organ cultures. Determining the distribution of espG and espG2 among clinical EPEC isolates revealed two different types of espG (espG alpha and espG beta) and espG2 (intact and pseudo genes), which were associated with specific EPEC serotypes and closely followed the EPEC lineage. This investigation has established a role for EspG2 in the disruption of the microtubule network and associated different espG and espG2 types with different groups of EPEC.     

The role of the interdomain B linker in the activation of the XylR protein of Pseudomonas putida

In the presence of toluene and other structural analogues, the enhancer binding protein XylR activates the sigma54 promoter Pu of the TOL (toluene degradation) plasmid pWW0 of Pseudomonas putida. Introduction of amino acid changes Val-219Asp and Ala-220Pro, which enter a proline kink at the interdomain region (B linker) between the A (signal reception) module and the central portion of XylR, originated a protein with unforeseen properties. These included a minor ability to activate Pu in the absence of aromatic effectors, a much higher responsiveness to m-xylene and a significant response to a large collection of aromatic inducers. Such changes could not be attributed to variations in XylR expression levels or to the fortuitous creation of a novel promoter, but to a genuine change in the properties of the activator. Structural predictions suggested that the mutation entirely disrupted an otherwise probable coiled-coil structure. A second directed mutant within the same region consisting of a major replacement of amino acids A220-N221 by the peptide HHHR produced an even more exacerbated phenotype. These data support a model in which the linker B region influences the effector profile by modifying at a distance the operative shape of the effector pocket and fixing the protein in an intermediate step of the activation process.     

Moderate drought influences the effect of arbuscular mycorrhizal fungi as biocontrol agents against Verticillium-induced wilt in pepper

Previous studies have shown that the arbuscular mycorrhizal fungus (AMF) Glomus deserticola (Trappe, Bloss and Menge) can diminish the negative effect of Verticillium dahliae Kleb. on pepper yield. On the other hand, it is known that AMF can be more beneficial for plant growth and physiology under dry conditions than when soil moisture is plentiful. Therefore, our objective was to assess if a moderate water deficit imposed on pepper plants before their inoculation with V. dahliae could improve the effectiveness of G. deserticola as biocontrol agent. In the present experiment, the delay in disease development in Verticillium-inoculated plants associated with AMF did not occur under well watered conditions. In addition, the establishment of mycorrhizal symbiosis and the development of structures by AMF were delayed when both symbiotic and pathogenic fungi infected the same root. Therefore, it is suggested that the equilibrium between pepper plant, G. deserticola and V. dahliae is so complex that small changes in competition between symbiotic and pathogenic fungi for host resources can modify the efficiency of AMF as a biocontrol agent. On the other hand, water deficit enhanced the deleterious effect of V. dahliae on fruit set and yield only when pepper plants were not associated with G. deserticola, which reinforces the idea that AMF may be more important for host plants subjected to stressful conditions. However, comparing well watered non-mycorrhizal and predroughted mycorrhizal plants, we found that moderate water deficit imposed before inoculation with V. dahliae did not improve the effectiveness of G. deserticola as a biocontrol agent.