Poly-3-hydroxybutyrate production by washed cells of Alcaligenes eutrophus; purification, characterisation and potential regulatory role of citrate synthase

Washed cells prepared from carbon-limited continuous cultures of Alcaligenes eutrophus synthesised poly-3-hydroxybutyrate (PHB) rapidly when supplied with glucose, dl-lactate or l-lactate. Unlike growing cultures, washed cells excreted significant amounts of pyruvate. The combined rates of PHB production (qPHB) and pyruvate excretion (qPyr) were linearly related to the rate of carbon substrate utilisation (qS), showing that washed cells behaved similarly to growing cultures when corrected for the absence of non-PHB biomass production. The addition of formate (as a potential source of NADH and/or ATP) significantly stimulated both qPHB and qPyr, but slightly decreased qS and substantially decreased the flux of carbon through the tricarboxylic acid cycle (qTCA). Citrate synthase activity of broken cells was inhibited by physiological concentrations of NADH, but not of ATP, in a manner that was not reversible by AMP. Citrate synthase was purified and shown to be a “large” form of the enzyme (M _r 227,000), comprising a single type of subunit (M _r 47,000) as found in several other gram-negative aerobes. The potential role of citrate synthase in the regulation of PHB production via its ability to control carbon flux into the tricarboxylic acid cycle is discussed. Received: 14 March 1997 / Accepted: 9 July 1997     

Genetic Diversity through the Looking Glass: Effect of Enrichment Bias

The effect of enrichment bias on the diversity of 2,4-dichlorophenoxyacetate (2,4-D)-degrading (2,4-D(sup+)) bacteria recovered from soil was evaluated by comparing the diversity of isolates obtained by direct plating to the diversity of isolates obtained from 85 liquid batch cultures. By the two methods, a total of 159 isolates were purified from 1 g of soil and divided into populations based on repeated extragenic palindromic sequence PCR (rep-PCR) genomic fingerprints. Approximately 42% of the direct-plating isolates hybridized with the tfdA and tfdB genes from Alcaligenes eutrophus JMP134(pJP4), 27% hybridized with the tfdA and tfdB genes from Burkholderia sp. strain RASC, and 30% hybridized with none of the probes. In contrast, the enrichment isolates not only represented fewer populations than the isolates obtained by direct plating but also exhibited, almost exclusively, a single hybridization pattern with 2,4-D catabolic gene probes. Approximately 98% of the enrichment isolates possessed pJP4-type tfdA and tfdB genes, whereas isolates containing RASC-type tfdA and tfdB genes were obtained from only 2 of the 85 enrichment cultures. The skewed occurrence of the pJP4-type genes among the isolates obtained by enrichment suggests that the competitive fitness of 2,4-D(sup+) populations during growth with 2,4-D may be influenced either by specific tfd alleles or by genetic factors linked to these alleles. Moreover, the results indicate that evaluation of the diversity and distribution of catabolic pathways in nature can be highly distorted by the use of enrichment culture techniques.     

Zinc efficiency of oilseed rape (t Brassica napus and t B. juncea) genotypes

Twenty five genotypes of oilseed rape (canola and mustard) were tested under varied supply of Zn (+Zn: 2 mg kg^–1 soil, -Zn: no Zn added) in two pot experiments in soil culture to determine the genotypic variation in tolerance to the Zn-deficient conditions, that is, to identify the Zn-efficient genotypes. On the basis of performance of genotypes in pot experiments, ten genotypes were tested in 1995 for their performance under varied supply of Zn (+Zn: 3.5 kg ha^–1, -Zn: no Zn added) on a Zn-deficient field in South Australia.Zn efficiency (ratio of shoot dry matter in -Zn to shoot dry matter in +Zn treatment and expressed in percentage) in pot Experiment 1 varied from 35% for 92-13 to 74% for Siren. Narendra, Dunkeld, Barossa, Oscar and Xinza 2 performed well under -Zn treatment. Zn efficiency in Experiment 2 varied from 32% for Wuyou 1 to 62% for Pusa Bold. Pusa Bold and CSIRO-1(mustard genotypes) were the most efficient in terms of dry matter production among all the oilseed rape genotypes tested. Root dry matter accumulation was significantly higher in Zn-efficient genotypes. Zn efficiency (ratio of seed yield in -Zn to seed yield in +Zn and expressed in percentage) in field experiment varied from 62% for Huashang 2 to 76% for Dunkeld. With few exceptions, the ranking of genotypes in pot and field experiments indicates similarity in their response to Zn deficiency. There looks to be genetic control over Zn concentration in tissues. Zn-efficient genotypes had lower Zn concentration in roots and higher Zn concentration in youngest fully opened leaf blades, indicating a better transport of Zn. This, together with a higher Zn uptake, appears to be the basis of expression of Zn efficiency.     

Saltatory search: a theoretical analysis

Many animal search in a saltatory fashion: they move forward,pause briefly, and move forward again. Although many optimal-foragingmodels have been developed, most do not address how an animalsearches for food. We view search strategies as "time-distance"functions to allow not only for the possibility of oscillationsin body speed, as implied by saltatory search, but other movementpatterns as well, including cruise search. The key feature ofour models is distinguishing between the body position and thescan position (where the forager is looking). We see the varyingmovement of saltatory search as a consequence of the curvaturein the functions that relate body speed to benefits (Jensen'sinequality)     

Numerical comparison of several approximations of the word count distribution in random sequences.

The exact distribution of word counts in random sequences and several approximations have been proposed in the past few years. The exact distribution has no theoretical limit but may require prohibitive computation time. On the other hand, approximate distributions can be rapidly calculated but, in practice, are only accurate under specific conditions. After making a survey of these distributions, we compare them according to both their accuracy and computational cost. Rules are suggested for choosing between Gaussian approximations, compound Poisson approximation, and exact distribution. This work is illustrated with the detection of exceptional words in the phage Lambda genome.     

The Distributed Annotation System

Background  

Currently, most genome annotation is curated by centralized groups with limited resources. Efforts to share annotations transparently among multiple groups have not yet been satisfactory.     

Thresholds of Response in Nest Thermoregulation by Worker Bumble Bees, Bombus bifarius nearcticus (Hymenoptera: Apidae)

Regulation of nest temperature is important to the fitness of eusocial insect colonies. To maintain appropriate conditions for the developing brood, workers must exhibit thermoregulatory responses to ambient temperature. Because nest-mate workers differ in task performance, thermoregulatory behavior provides an opportunity to test threshold of response models for the regulation of division of labor. We found that worker bumble bees ( Bombus bifarius nearcticus ) responded to changes in ambient temperature by altering their rates of performing two tasks – wing fanning and brood cell incubation. At the colony level, the rate of incubating decreased, and the rate of fanning increased, with increasing temperature. Changes in the number of workers performing these tasks were more important to the colony response than changes in workers' task performance rates. At the individual level, workers' lifetime rates of incubation and fanning were positively correlated, and most individuals did not specialize exclusively on either of these temperature-sensitive tasks. However, workers differed in the maximum temperature at which they incubated and in the minimum temperature at which they fanned. More individuals fanned at high and incubated at low temperatures. Most of the workers that began incubating at higher temperatures continued performing this task at lower temperatures, when additional nest-mates became active. The converse was true for fanning behavior. These data are consistent with a threshold of response model for thermoregulatory behavior of B. bifarius workers.     

The disease business

A report on the 'Host-Pathogen Interactions' minisymposium at the first meeting of the European Life Scientist Organization (ELSO), Geneva, Switzerland, September 2-6, 2000.