University of São Paulo

About: University of São Paulo is a education organization based out in São Paulo, Brazil. It is known for research contribution in the topics: Population & Health care. The organization has 136513 authors who have published 272320 publications receiving 5127869 citations. The organization is also known as: USP & Universidade de São Paulo.

Distribution of nitrogen fixation and nitrogenase-like sequences amongst microbial genomes

Abstract: The metabolic capacity for nitrogen fixation is known to be present in several prokaryotic species scattered across taxonomic groups. Experimental detection of nitrogen fixation in microbes requires species-specific conditions, making it difficult to obtain a comprehensive census of this trait. The recent and rapid increase in the availability of microbial genome sequences affords novel opportunities to re-examine the occurrence and distribution of nitrogen fixation genes. The current practice for computational prediction of nitrogen fixation is to use the presence of the nifH and/or nifD genes. Based on a careful comparison of the repertoire of nitrogen fixation genes in known diazotroph species we propose a new criterion for computational prediction of nitrogen fixation: the presence of a minimum set of six genes coding for structural and biosynthetic components, namely NifHDK and NifENB. Using this criterion, we conducted a comprehensive search in fully sequenced genomes and identified 149 diazotrophic species, including 82 known diazotrophs and 67 species not known to fix nitrogen. The taxonomic distribution of nitrogen fixation in Archaea was limited to the Euryarchaeota phylum; within the Bacteria domain we predict that nitrogen fixation occurs in 13 different phyla. Of these, seven phyla had not hitherto been known to contain species capable of nitrogen fixation. Our analyses also identified protein sequences that are similar to nitrogenase in organisms that do not meet the minimum-gene-set criteria. The existence of nitrogenase-like proteins lacking conserved co-factor ligands in both diazotrophs and non-diazotrophs suggests their potential for performing other, as yet unidentified, metabolic functions. Our predictions expand the known phylogenetic diversity of nitrogen fixation, and suggest that this trait may be much more common in nature than it is currently thought. The diverse phylogenetic distribution of nitrogenase-like proteins indicates potential new roles for anciently duplicated and divergent members of this group of enzymes.

Can Lignin Be Accurately Measured

Abstract: too simplistic (Sarkanen and Ludwig, 1971), and there are now many examples showing that other phenolics Foragesserve animportant rolein providingnutrients toruminants besides the cinnamyl alcohols can be incorporated into while providing positive benefits to the environment. Forage cell wall digestibility is incomplete because of several structural features within lignins (as reviewed by Sederoff et al., 1999). From a the wall, but digestion is mostly inversely correlated with the amount functional point of view, lignins impart strength to cell of lignification that has occurred during cell wall development. Lignin walls, facilitate water transport, and impede the degrais a hydrophobic polymer formed through enzyme-mediated radical dation of wall polysaccharides, thus acting as a major coupling of monolignols, mainly coniferyl and sinapyl alcohols. The lineof defenseagainstpathogens, insects,and otherherpolymerishighlyresistanttodegradationandgenerallypassesthrough bivores. the ruminant unmodified. Though lignin is resistant to degradation, It is important, no matter which definition you prefer, it is not easily quantified within various types of forages. Numerous to be able to determine the concentration of lignin methods have been developed over the years to measure lignin levels within a wide range of cell wall types. Since lignin is in different plant species. Most frequently used among workers infairly resistant to both chemical and biological degradavolved with forage development or utilization are the acid detergent, Klason, and permanganate lignin methods. More recently, acetyl bro- tion, one would think that it would be relatively easy midehasreceivedattentionasapossiblelignindeterminationmethod. to measure (Sarkanen and Ludwig, 1971). Lignin has The acetyl bromide method is dependent on determining the ab- been defined, at least in general chemical terms, for sorbance of the extract in which all the lignin of a sample has been 50 yr and several well-defined procedures to quantify dissolved. Each of these methods gives different lignin values for the lignin in plant tissues have been developed and apsame type of forage sample. For example, acid detergent, Klason, proved as AOAC (Association of Analytical Communipermanganate, and acetyl bromide lignin methods give quite different ties International formerly Association of Official Anavalues for alfalfa stems: 93, 145, 158, and 135 g lignin kg 1