Prior Infection Does Not Improve Survival against the Amphibian Disease Chytridiomycosis

Many amphibians have declined globally due to introduction of the pathogenic fungus Batrachochytrium dendrobatidis (Bd). Hundreds of species, many in well-protected habitats, remain as small populations at risk of extinction. Currently the only proven conservation strategy is to maintain species in captivity to be reintroduced at a later date. However, methods to abate the disease in the wild are urgently needed so that reintroduced and wild animals can survive in the presence of Bd. Vaccination has been widely suggested as a potential strategy to improve survival. We used captive-bred offspring of critically endangered booroolong frogs (Litoria booroolongensis) to test if vaccination in the form of prior infection improves survival following re exposure. We infected frogs with a local Bd isolate, cleared infection after 30 days (d) using itraconazole just prior to the onset of clinical signs, and then re-exposed animals to Bd at 110 d. We found prior exposure had no effect on survival or infection intensities, clearly showing that real infections do not stimulate a protective adaptive immune response in this species. This result supports recent studies suggesting Bd may evade or suppress host immune functions. Our results suggest vaccination is unlikely to be useful in mitigating chytridiomycosis. However, survival of some individuals from all experimental groups indicates existence of protective innate immunity. Understanding and promoting this innate resistance holds potential for enabling species recovery.     

Biochanin A improves fibre fermentation by cellulolytic bacteria

Aims

The objective was to determine the effect of the isoflavone biochanin A (BCA) on rumen cellulolytic bacteria and consequent fermentative activity.

Methods and Results

When bovine microbial rumen cell suspensions (n = 3) were incubated (24 h, 39°C) with ground hay, cellulolytic bacteria proliferated, short‐chain fatty acids were produced and pH declined. BCA (30 μg ml^?1) had no effect on the number of cellulolytic bacteria or pH, but increased acetate, propionate and total SCFA production. Addition of BCA improved total digestibility when cell suspensions (n = 3) were incubated (48 h, 39°C) with ground hay, Avicel, or filter paper. Fibrobacter succinogenes S85, Ruminococcus flavefaciens 8 and Ruminococcus albus 8 were directly inhibited by BCA. Synergistic antimicrobial activity was observed with BCA and heat killed cultures of cellulolytic bacteria, but the effects were species dependent.

Conclusions

These results indicate that BCA improves fibre degradation by influencing cellulolytic bacteria competition and guild composition.

Significance and Impact of the Study

BCA could serve as a feed additive to improve cellulosis when cattle are consuming high‐fibre diets. Future research is needed to evaluate the effect of BCA on fibre degradation and utilization in vivo.     

Replication slippage may cause parallel evolution in the secondary structures of mitochondrial transfer RNAs

Presence of the dihydrouridine (D) stem in the mitochondrial cysteine tRNA is unusually variable among lepidosaurian reptiles. Phylogenetic and comparative analyses of cysteine tRNA gene sequences identify eight parallel losses of the D-stem, resulting in D-arm replacement loops. Sampling within the monophyletic Acrodonta provides no evidence for reversal. Slipped-strand mispairing of noncontiguous repeated sequences during replication or direct replication slippage can explain repeats observed within cysteine tRNAs that contain a D-arm replacement loop. These two mechanisms involving replication slippage can account for the loss of the cysteine tRNA D-stem in several lepidosaurian lineages, and may represent general mechanisms by which the secondary structures of mitochondrial tRNAs are altered.      

Effects of growth rate and influent substrate concentration on effluent quality from chemostats containing bacteria in pure and mixed culture

Studies were performed using pure cultures of A. acrogenes and E. coli and a heterogeneous microbial population growing in carbon-limited chemostats with glucose as the sole carbon and energy source. A two-level factorial experimental design was employed to test the hypothesis that the concentration of growth-limiting substrate in a chemostat is controlled by the growth rate alone and is independent of the concentration of substrate entering the reactor. The pure culture experiments showed that the conclusions depend upon the measurement employed for growth-limiting substrate. When the concentration of glucose was measured directly, the hypothesis was found to be true within the limits of the study (500–1500 mg/liter). However, if the chemical oxygen demand (COD) test was used as the measure of growth-limiting substrate the hypothesis was found to be false. When heterogeneous cultures were employed the hypothesis was false regardless of the technique used to measure the concentration of growth-limiting substrate. Nevertheless, it was possible to generate regression equations which described the interactions among influent COD, growth rate, and effluent COD with a high level of correlation.     

Adoption of single and multiple infants by rhesus monkey mothers

Adoption was studied inMacaca mulatta. Multiparous mothers were separated from their biological offspring within hours following parturition, and 2 1/2 days later, on the average, they were offered neonates for adoption. These foster infants had been separated from their biological mothers shortly after birth and averaged 2 3/4 days old when subjected to adoption. Mothers that were offered a single neonate immediately and completely adopted the foster infant. But mothers that were offered two infants at the same time were ambivalent. Many infants were rejected initially, although with one partial exception, the mothers eventually accepted and cared for two infants. It was concluded that the macaque maternal affectional system may be biased toward accepting and nurturing one infant at a time.     

Overexpression of Bacillus subtilis phosphoribosylpyrophosphate synthetase and crystallization and preliminary X-ray characterization of the free enzyme and its substrate–effector complexes

Bacillus subtilis phosphoribosylpyrophosphate (PRPP) synthetase has been expressed to high levels in an Escherichia coli host strain devoid of endogenous PRPP synthetase. A rapid and efficient purification protocol has been developed allowing production of enzyme preparations with purity conforming to the stringent criteria required for crystallization. Crystallization experiments, in combination with dynamic light scattering studies, have led to the production of three crystal forms of the enzyme. These forms include the free enzyme, the enzyme in a binary complex with the substrate adenosine triphosphate (ATP), and the enzyme in a quaternary complex with the substrate analog α, β-methylene adenosine triphosphate (mATP), the substrate ribose-5-phosphate (Rib-5-P), and the allosteric inhibitor adenosine diphosphate (ADP). Diffraction data showed that all three crystal forms are suitable for structure determination. They crystallize in the same hexagonal space group, P6₃, with virtually identical unit cell dimensions of a = b = 115.6 Å c = 107.8 Å, and with two molecules in the asymmetric unit. The self-rotation function showed the existence of a non-crystallographic twofold axis perpendicular to the c axis. The availability of the different complexes should allow questions regarding the molecular mechanisms of catalysis and allostery in PRPP synthetase to be addressed.