Nutrient requirements of dairy cattle , Nutrient requirements of dairy cattle , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Nutrient requirements of dairy cattle

Mechanisms and applications of plant growth promoting rhizobacteria: Current perspective

Physical and mechanical properties of PLA, and their functions in widespread applications - A comprehensive review.

Poly(lactic acid) (PLA), so far, is the most extensively researched and utilized biodegradable aliphatic polyester in human history. Due to its merits, PLA is a leading biomaterial for numerous applications in medicine as well as in industry replacing conventional petrochemical-based polymers. The main purpose of this review is to elaborate the mechanical and physical properties that affect its stability, processability, degradation, PLA-other polymers immiscibility, aging and recyclability, and therefore its potential suitability to fulfill specific application requirements. This review also summarizes variations in these properties during PLA processing (i.e. thermal degradation and recyclability), biodegradation, packaging and sterilization, and aging (i.e. weathering and hygrothermal). In addition, we discuss up-to-date strategies for PLA properties improvements including components and plasticizer blending, nucleation agent addition, and PLA modifications and nanoformulations. Incorporating better understanding of the role of these properties with available improvement strategies is the key for successful utilization of PLA and its copolymers/composites/blends to maximize their fit with worldwide application needs.

Physical and mechanical properties of PLA, and their functions in widespread applications — A comprehensive review

Application of prebiotics and probiotics in poultry production

The microbiota of the intestinal tract of chickens plays an important role in inhibiting the establishment of intestinal pathogens. Earlier culturing and microscopic examinations indicated that only a fraction of the bacteria in the cecum of chickens could be grown in the laboratory. Therefore, a survey of cecal bacteria was done by retrieval of 16S rRNA gene sequences from DNA isolated from the cecal content and the cecal mucosa. The ribosomal gene sequences were amplified with universal primers and cloned or subjected to temporal temperature gradient gel electrophoresis (TTGE). Partial 16S rRNA gene sequences were determined from the clones and from the major bands in TTGE gels. A total of 1,656 partial 16S rRNA gene sequences were obtained and compared to sequences in the GenBank. The comparison indicated that 243 different sequences were present in the samples. Overall, sequences representing 50 phylogenetic groups or subgroups of bacteria were found, but approximately 89% of the sequences represented just four phylogenetic groups (Clostridium leptum, Sporomusa sp., Clostridium coccoides, and enterics). Sequences of members of the Bacteroides group, the Bifidobacterium infantis subgroup, and of Pseudomonas sp. each accounted for less than 2% of the total. Sequences related to those from the Escherichia sp. subgroup and from Lactobacillus, Pseudomonas, and Bifidobacterium spp. were generally between 98 and 100% identical to sequences already deposited in the GenBank. Sequences most closely related to those of the other bacteria were generally 97% or less identical to those in the databases and therefore might be from currently unknown species. TTGE and random cloning indicated that certain phylogenetic subgroups were common to all birds analyzed, but sequence data from random cloning also provided evidence for qualitative and quantitative differences among the cecal microbiota of individual birds reared under very similar conditions.

16S rRNA-Based Analysis of Microbiota from the Cecum of Broiler Chickens

Alternatives to antibiotics: bacteriocins, antimicrobial peptides and bacteriophages

A tremendous effort has been made over the last decade to develop and test films with antimicrobial properties to improve food safety and shelf life. This review catalogues and analyses the outcome of these research efforts. The bacteriocin nisin was the antimicrobial most commonly incorporated into films, followed by food-grade acids and salts, chitosan, plant extracts, and the enzymes lysozyme and lactoperoxidase. The methodologies for measuring antimicrobial activity of both edible and inedible films varied considerably among the studies. Results, defined as the difference in the log10 colony-forming unit (CFU) of a test organism exposed to a control film and the log10 CFU of the organism exposed to the antimicrobial film, ranged from 0 to 9 for many of the antimicrobials tested. Even for antimicrobials such as nisin, chitosan or antimicrobial acids with a ‘long’ history of studying their incorporation into antimicrobial films, the majority of results centred around 2 log10 reductions. The results suggest that antimicrobial films still face limitations and are perhaps still best viewed as part of a hurdle strategy to provide safe foods. Copyright © 2007 John Wiley & Sons, Ltd.

Antimicrobial films for food applications: a quantitative analysis of their effectiveness

The nucleotide sequence of a region of the Azotobacter vinelandii genome exhibiting sequence similarity to nifH has been determined. The order of open reading frames within this 6.1-kilobase-pair region was found to be anfH (alternative nitrogen fixation, nifH-like gene), anfD (nifD-like gene), anfG (potentially encoding a protein similar to the product of vnfG from Azotobacter chroococcum), anfK (nifK-like gene), followed by two additional open reading frames. The 5'-flanking region of anfH contains a nif promoter similar to that found in the A. vinelandii nifHDK gene cluster. The presumed products of anfH, anfD, and anfK are similar in predicted Mr and pI to the previously described subunits of nitrogenase 3. Deletion plus insertion mutations introduced into the anfHDGK region of wild-type strain A. vinelandii CA resulted in mutant strains that were unable to grow in Mo-deficient, N-free medium but grew in the presence of 1 microM Na2MoO4 or V2O5. Introduction of the same mutations into the nifHDK deletion strain CA11 resulted in strains that grew under diazotrophic conditions only in the presence of vanadium. The lack of nitrogenase 3 subunits in these mutant strains was demonstrated through two-dimensional gel analysis of protein extracts from cells derepressed for nitrogenase under Mo and V deficiency. These results indicate that anfH, anfD, and anfK encode structural proteins for nitrogenase 3.

Nucleotide sequence and mutational analysis of the structural genes (anfHDGK) for the second alternative nitrogenase from Azotobacter vinelandii.

INTRODUCTION 109 BRIEF OVERVIEW OF THE GENETICS OF MOLYBDENUM-CONTAINING NITROGENASES ..... . . . .. . . . . . 111 IDENTIFICATION AND ORGANIZATION OF GENES REQUIRED FOR MOLYBDENUM-INDEPENDENT NITROGENASES. . . . . ...... . . . . . .. . . . . ..... II3 nif Genes Shared by the Three Nitrogenase Systems in Azotobacter vinelandii...... 113 Genes Encoding Nitrogenase 2 . 115 Genes Encoding Nitrogenase 3 . ....... ......... . . ... ...... 116 Sequence Comparisons Between Structural Genes . . . . . . . . . . . . . . . . ... . . . . . . . . . . ... . . . . . . . . . 116 Nonstructural Genes.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . ..... . . . 118 REGULATION OF EXPRESSION OF THE ALTERNATIVE Nz FIXATION SySTEMS 119 CONCLUDING REMARKS 120

Rolf D. Joerger

Papers

16S rRNA-Based Analysis of Microbiota from the Cecum of Broiler Chickens

Alternatives to antibiotics: bacteriocins, antimicrobial peptides and bacteriophages

Antimicrobial films for food applications: a quantitative analysis of their effectiveness

Nucleotide sequence and mutational analysis of the structural genes (anfHDGK) for the second alternative nitrogenase from Azotobacter vinelandii.

Genetics and Molecular Biology of Alternative Nitrogen Fixation Systems