A new batch calorimeter for aerobic growth studies

A microcalorimeter for aerobic growth studies, derived from a Tian Calvet differential apparatus, was successfully constructed. The calorimetric vessel was a short cylinder, which permitted a good exchange between the surface area and the gas phase. The time constant of the calorimeter was 3.6 min and the sensitivity 234 V/W. The thermochemical aspect of the aerobic growth of Escherichia coli on succinate, acetate, and glucose was investigated. This analysis revealed that the contribution of biosynthetic reactions varied with the substrate used and strongly influenced the heat evolution. The experimental metabolic enthalpy change was in good agreement with the predicted value for succinate and glucose growth. To explain the discrepancy between the two values observed for acetate growth we suggest that acetate metabolism may generate a by-product which was not further oxidized.     

Metabolism and Solubilization of Cellulose by Clostridium cellulolyticum H10

When Clostridium cellulolyticum was grown with cellulose MN300 as the substrate, the rates of growth and metabolite production were found to be lower than those observed with soluble sugars as the substrate. At low cellulose concentrations, the growth yields were equal to those obtained with cellobiose. The main fermentation products from cellulose and soluble sugars were the same. Up to 15 mM of consumed hexose, a change in the metabolic pathway favoring lactate production similar to that observed with soluble sugars was found to occur concomitantly with a decrease in molar growth yield. With cellulose concentrations above 5 g/liter, accumulation of soluble sugars occurred once growth had ceased. Glucose accounted for 30% of these sugars. A kinetic analysis of cellulose solubilization revealed that cellulolysis by C. cellulolyticum involved three stages whatever cellulose concentration was used. Analysis of these kinetics showed three consecutive enzymatic activity levels having the same K_m (0.8 g of cellulose per liter, i.e., 5 mM hexose equivalent) but decreasing values of V_max. The hypothesis is suggested that each step corresponds to differences in cellulose structure.     

Multiple controls exerted on in vivo expression of the pepN gene in Escherichia coli: studies with pepN-lacZ operon and protein fusion strains.

Lipoteichoic acid (LTA) from Lactobacillus casei contains poly(glycerophosphate) substituted with D-alanyl ester residues. The distribution of these residues in the in vitro-synthesized polymer is uniform. Esterification of LTA with D-alanine may occur in one of two modes: (i) addition at random or (ii) addition at a defined locus in the poly(glycerophosphate) chain followed by redistribution of the ester residues. A time-dependent transacylation of these residues from D-[14C]alanyl-lipophilic LTA to hydrophilic acceptor was observed. The hydrophilic acceptor was characterized as D-alanyl-hydrophilic LTA. This transacylation requires neither ATP nor the D-alanine incorporation system, i.e., the D-alanine activating enzyme and D-alanine:membrane acceptor ligase. No evidence for an enzyme-catalyzed transacylation reaction was observed. We propose that this process of transacylation may be responsible for the redistribution of D-alanyl residues after esterification to the poly(glycerophosphate). As a result, it is difficult to distinguish between these proposed modes of addition.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Microcalorimetric evaluation of the efficacy of the alkaline treatment on the fermentation of straw

Summary A microcalorimetric study is proposed to follow the degradation of straw by a mixed bacterial culture. The effect of an alkali pretreatment of straw is described.     

Microcalorimetric study of Escherichia coli aerobic growth: theoretical aspects of growth on succinic acid.

Two methods of investigation were used to evaluate the heat quantity associated with anabolic processes (qan) during the aerobic growth of Escherichia coli in a minimal medium containing succinic acid as the sole energy and carbon source. The study of the contribution of biosynthetic reactions from succinic acid and ammonia were investigated by both methods. The two qan values obtained were in excellent agreement and were found to be significant. Thus it was demonstrated that the contribution of anabolism strongly influenced the quantity of heat associated with microbial aerobic growth. The qan calculated as above explained the experimental enthalpy change which was recently reported.     

(Study on the beta-galactoside permease of Escherichia coli). Solubilization of a thiodigalactoside-binding protein from E.coli membrane containing beta-galactoside permease.

A thiodigalactoside binding protein is solubilized from membrane vesicles of $\text{Escherichia}\text{Coli}$ containing the M protein by use of the detergents Triton X-100 or Emulfogen BC 720. Thiodigalactoside binding affinity of the soluble protein is the same as the membrane embedded β-galactoside permease whereas the residual particulate fraction is free of affinity for this substrate.     

What can we learn from noncoding regions of similarity between genomes?

Background  

In addition to known protein-coding genes, large amounts of apparently non-coding sequence are conserved between the human and mouse genomes. It seems reasonable to assume that these conserved regions are more likely to contain functional elements than less-conserved portions of the genome.