Experience matters: prior exposure to plant toxins enhances diversity of gut microbes in herbivores

For decades, ecologists have hypothesised that exposure to plant secondary compounds (PSCs) modifies herbivore‐associated microbial community composition. This notion has not been critically evaluated in wild mammalian herbivores on evolutionary timescales. We investigated responses of the microbial communities of two woodrat species (Neotoma bryanti and N. lepida). For each species, we compared experienced populations that independently converged to feed on the same toxic plant (creosote bush, Larrea tridentata) to naïve populations with no exposure to creosote toxins. The addition of dietary PSCs significantly altered gut microbial community structure, and the response was dependent on previous experience. Microbial diversity and relative abundances of several dominant phyla increased in experienced woodrats in response to PSCs; however, opposite effects were observed in naïve woodrats. These differential responses were convergent in experienced populations of both species. We hypothesise that adaptation of the foregut microbiota to creosote PSCs in experienced woodrats drives this differential response.     

Proteomic studies highlight outer‐membrane proteins related to biofilm development in the marine bacterium Pseudoalteromonas sp. D41

Bacterial biofilm development is conditioned by complex processes involving bacterial attachment to surfaces, growth, mobility, and exoproduct production. The marine bacterium Pseudoalteromonas sp. strain D41 is able to attach strongly onto a wide variety of substrates, which promotes subsequent biofilm development. Study of the outer‐membrane and total soluble proteomes showed ten spots with significant intensity variations when this bacterium was grown in biofilm compared to planktonic cultures. MS/MS de novo sequencing analysis allowed the identification of four outer‐membrane proteins of particular interest since they were strongly induced in biofilms. These proteins are homologous to a TonB‐dependent receptor (TBDR), to the OmpW and OmpA porins, and to a type IV pilus biogenesis protein (PilF). Gene expression assays by quantitative RT‐PCR showed that the four corresponding genes were upregulated during biofilm development on hydrophobic and hydrophilic surfaces. The Pseudomonas aeruginosa mutants unable to produce any of the OmpW, OmpA, and PilF homologues yielded biofilms with lower biovolumes and altered architectures, confirming the involvement of these proteins in the biofilm formation process. Our results indicate that Pseudoalteromonas sp. D41 shares biofilm formation mechanisms with human pathogenic bacteria, but also relies on TBDR, which might be more specific to the marine environment.     

More than 400 million years of evolution and some plants still can't make it on their own: plant stress tolerance via fungal symbiosis

All plants in natural ecosystems are thought to be symbioticwith mycorrhizal and/or endophytic fungi. Collectively, thesefungi express different symbiotic lifestyles ranging from parasitismto mutualism. Analysis of Colletotrichum species indicates thatindividual isolates can express either parasitic or mutualisticlifestyles depending on the host genotype colonized. The endophytecolonization pattern and lifestyle expression indicate thatplants can be discerned as either disease, non-disease, or non-hosts.Fitness benefits conferred by fungi expressing mutualistic lifestylesinclude biotic and abiotic stress tolerance, growth enhancement,and increased reproductive success. Analysis of plant–endophyteassociations in high stress habitats revealed that at leastsome fungal endophytes confer habitat-specific stress toleranceto host plants. Without the habitat-adapted fungal endophytes,the plants are unable to survive in their native habitats. Moreover,the endophytes have a broad host range encompassing both monocotsand eudicots, and confer habitat-specific stress tolerance toboth plant groups. Key words: Colletotrichum, fungal endophytes, stress tolerance, symbiosis, symbiotic lifestyle Received 19 June 2007; Revised 25 November 2007 Accepted 30 November 2007     

石油降解细菌降解条件优化研究

采用富集培养法从工业油污土壤中分离到1株能以石油为惟一碳源而生长的细菌菌株,采用正交设计实验对该菌株的降解条件进行了初步研究。结果表明,最佳降解条件为NH_4Cl 4.0 g/LL,K_2HPO_4 1.5 g/L,pH 8.0,NaCl 15.0 g/L。在最佳条件下,浓度为1 mL/L的原油可在4 d内降解50%以上。     

The function of three indigenous plasmids in Mtesorhizobium huakuii 2020 and its symbiotic interaction with Sym pJB5JI of Rhizobium leguminosarum

A Mesorhizobium huakuii strain 2020, isolated from a rice-growing field in southern China, contains three indigenous plasmids named p2020a, p2020b and p2020c, respectively. The plasmids were deleted via Tn5-sacB insertion, and two cured derivatives were obtained. Interestingly, the mutant 2020D29 curing of p2020c could significantly enhance the capacity of symbiotic nitrogen fixation. But the mutant 2020D8 curing of p2020b lost the ability to nodulate Astragalus sinicus. Furthermore, the third plasmid p2020a could be hardly eliminated, suggesting that some house-keeping genes necessary for strain growth located on this plasmid. Then the Sym plasmid pJB5JI of R. leguminosarum bv. viciae was transferred into 2020 and its cured derivatives. The pot plant test showed that the ability of competition and symbiotic nitrogen fixation of transconjugant 2020-137 (pJB5JI) was increased evidently in con-trast to 2020. pJB5JI could not restore the ability of 2020D8 to nodulate Astragalus sinicus. 2020D8-8 (pJB5JI) could form ineffective nodules on peas, which implied that the symbiotic plasmid pJB5JI could express its function at the chromosomal background of Mesorhizobium huakuii 2020. The plas-mid stability was checked in transconjugants under free-living and during symbiosis. The results indi-cated that pJB5JI failed to be detected in some nodule isolates. That Km resistance gene could be am-plified from all transconjugants and nodule isolates suggested that pJB5JI was fully or partially inte-grated into the chromosome of recipients.     

Probing binding site of bacteriochlorophyll a and carotenoid in the reconstituted LH1 complex from Rhodospirillum rubrum S1 by Stark spectroscopy

Stark spectroscopy is a powerful technique to investigate the electrostatic interactions between pigments as well as between the pigments and the proteins in photosynthetic pigment–protein complexes. In this study, Stark spectroscopy has been used to determine two nonlinear optical parameters (polarizability change Tr(Δα) and static dipole-moment change |Δμ| upon photoexcitation) of isolated and of reconstituted LH1 complexes from the purple photosynthetic bacterium, Rhodospirillum (Rs.) rubrum. The integral LH1 complex was prepared from Rs. rubrum S1, while the reconstituted complex was assembled by addition of purified carotenoid (all-trans-spirilloxanthin) to the monomeric subunit of LH1 from Rs. rubrum S1. The reconstituted LH1 complex has its Q_y absorption maximum at 878 nm. This is shifted to the blue by 3 nm in comparison to the isolated LH1 complex. The energy transfer efficiency from carotenoid to bacteriochlorophyll a (BChl a), which was determined by fluorescence excitation spectroscopy of the reconstituted LH1 complex, is increased to 40%, while the efficiency in the isolated LH1 complex is only 28%. Based on the differences in the values of Tr(Δα) and |Δμ|, between these two preparations, we can calculate the change in the electric field around the BChl a molecules in the two situations to be E _Δ ≈ 3.4 × 10⁵ [V/cm]. This change can explain the 3 nm wavelength shift of the Q_y absorption band in the reconstituted LH1 complex.     

Characterization of aldehyde oxidase from <Emphasis Type="Italic">Brevibacillus</Emphasis> sp. MEY43 and its application to oxidative removal of glutaraldehyde

Bacterium MEY43, an isolate from soil, produced aldehyde oxidase when it was cultivated in a medium containing methanol as a sole source of carbon and energy. The methylotrophic bacterium was identified as Brevibacillus sp. Its cultivation in media containing other substrates, such as ethanol and glucose, resulted in little production of the enzyme. Aldehyde oxidase purified from a cell-free extract of the bacterium was a hetero-trimeric protein comprised of large, medium, and small subunits with molecular masses of 87, 35, and 19 kDa, respectively. Its UV/visible spectrum and the presence of molybdenum, 5′-CMP, flavin adenine dinucleotide, iron, and acid-labile sulfur suggested that the enzyme belonged to the xanthine oxidase family. The enzyme acted on a wide range of aliphatic and aromatic aldehydes. The K _m value for formaldehyde was 32 mM, whereas those for the other aldehydes tested were below 0.2 mM. When 10 mM glutaraldehyde was treated with 2.0 units of the enzyme ml⁻¹ in the presence of 100 units ml⁻¹ catalase for 120 min, the concentration of the aldehyde decreased to below a detectable level.     

Fungal endophyte infection changes growth attributes in Lolium multiflorum Lam

Abstract Lolium multiflorum is a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodium sp.) from early successional stages. We assessed the effect of Neotyphodium infection on the biology of L. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non‐competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands.     

海绵细菌B25W最佳产抗培养基及发酵条件的研究

从辽宁海域的繁茂膜海绵(Hymeniacidonperleve)中分离到1株解淀粉类芽孢杆菌(Paenibacillusamyloliquefaciens),定名为海绵细菌B25W。它产生的抗生素用白色念珠菌(Candidaalbicans)为指示菌,通过单因子和均匀设计实验,发现菌株最佳产抗摇瓶发酵培养基:玉米面0.34%,豆饼粉1.66%,葡萄糖0.1%,ZnSO40.04%,MgSO40.02%,KH2PO40.04%;发酵条件:种龄12h,接种量10%,发酵时间20h,初始pH6.0,250mL三角瓶内含25mL培养基,往复式摇床,116次/min,振幅11cm,培养温度28℃。应用二剂量法(以制霉菌素为标样)测定B25W抗生素的相对效价为13680u/mL,比优化前效价(8444u/mL)提高了62%。