The heyday of continuous culture was in the 1960s, when its versatility and reproducibility were used to address fundamental problems in diverse microbiological fields such as biochemistry, ecology, genetics and physiology. The advent of molecular genetics in the 1970s and 1980s led to a decline in the popularity of continuous culture as a standard laboratory tool. The current trend of studying global proteomics, transcriptomics and metabolomics requires reproducible, reliable and biologically homogeneous datasets with which to approach a given problem. The use of continuous culture techniques can aid the acquisition of such data, and continuous cultures offer advantages over biologically heterogeneous batch cultures, where secondary growth and stress effects can often mask subtle physiological differences and trends. This review is intended to remind microbiologists of the value of continuous cultivation in a wide range of biological investigations, and describes some advantages and recent advances in applications of continuous culture in post-genomic studies.

No abstract

No abstract

Trichomonas vaginalis is the etiological agent of trichomoniasis, the most prevalent non-viral sexually transmitted disease worldwide. Trichomoniasis is a widespread, global health concern, and occurring at an increasing rate. Infections of the female genital tract can cause a range of symptoms, including vaginitis and cervicitis, whilst infections in males are generally asymptomatic. The relatively mild symptoms, and lack of evidence for any serious sequelae, have historically led to this disease being under diagnosed, and under researched. However, growing evidence that T. vaginalis infection is associated with disease states with high morbidity in both men and women has increased the efforts to diagnose and treat patients harbouring this parasite. The pathology of trichomoniasis results from damage to the host epithelia, caused by a variety of processes during infection, and recent work has highlighted the complex interactions between the parasite and host, commensal microbiome, and accompanying symbionts. The commercial release of a number of nucleic acid amplification tests (NAATs) has added to the available diagnostic options. Immunoassay based Point of Care testing is currently available, and a recent initial evaluation of a NAAT Point of Care system has given promising results, which would enable testing and treatment in a single visit.

~_ _ _ _ _ _~ _ _ _ _ _ _ _~The production of the pigments actinorhodin and undecylprodigiosin by Stveptomyces coelicolor A3(2) was examined in a chemically defined medium which permits dispersed growth of the organism. The physiological controls on the production of the two pigments were markedly disparate. Actinorhodin production occurred mainly in the stationary phase of batch cultures grown with glucose and sodium nitrate as the principal carbon and nitrogen sources. In the same batch cultures, undecylprodigiosin accumulated during the exponential growth phase. The production of both pigments was sensitive to the levels of ammonium and phosphate in the medium. Actinorhodin production was exquisitely sensitive to ammonium concentration, and was completely inhibited by as little as 1 mM-ammonium chloride, whereas more than 50 mhl-amnonium chloride was required to prevent undecylprodigiosin production. A similar, but less extreme effect was seen with phosphate: actinorhodin production was completely inhibited by 24 mM-phosphate, whereas undecylprodigiosin was still formed at this high phosphate concentration. The effects of ammonium inhibition of pigmented antibiotic production were relieved by reducing the concentration of phosphate in the medium, but changing the ammonium concentration had no effect on phosphate inhibition. Thus the regulation of pigment production by these two nutrients is interrelated, with phosphate control being epistatic to that of ammonium. The results implicate a phosphorylated intermediate as a major regulator of secondary metabolite synthesis by S. coelicolor.

A physiological and molecular biological study was made of the control of methylenomycin biosynthesis by Streptomyces coelicolor A3(2). A simple and reliable assay for this antibiotic was developed. Conditions that permit the synthesis of methylenomycin by S. coelicolor cultures grown in defined medium were elucidated: a readily assimilated carbon and nitrogen source is required. Under these conditions methylenomycin is produced late in the growth phase, at the time of transition from exponential to linear growth. Provided that the phosphate concentration in the medium is kept high, there is synthesis of methylenomycin but not of the other secondary metabolites that this strain can produce. These conditions were used to study the transcription of the methylenomycin gene cluster during the transition from primary to secondary metabolism. The biosynthetic genes of at least one of the mmy transcription units appear to be transcribed before the mmr resistance determinant. The possibility that methylenomycin induces the transcription of mmr is discussed.

The degree of overrepresentation of selected chromosomal genes in rapidly growing cultures of Streptomyces coelicolor was assessed by quantitative DNA hybridization analysis. The results are consistent with the hypothesis that the principal origin of replication is close to the dnaA-gyrB region, in the center of the linear chromosome, and that replication proceeds bidirectionally.The streptomycete bacteria are among the most complex members of the prokaryotic world and possess large (ca. 8 Mb [11]) linear genomes (12, 13). Since the Streptomyces coelicolor chromosome is linear, it cannot be assumed that its mode of replication will be the same as that of other bacteria, such as Escherichia coli or Bacillus subtilis. Any investigation of the mode of chromosomal replication in Streptomyces species is hampered by a number of methodological and physiological problems which are not encountered with unicellular bacteria. For instance, the mycelial growth habit of streptomycetes means that synchronous cultures are difficult or impossible to prepare, while thymine-requiring mutants, which enable the specific labelling of DNA (15,17), are lacking for this genus (8). In an attempt to circumvent these difficulties, we have used quantitative DNA-DNA hybridization analysis, with specific gene probes from both homologous and heterologous sources, in order to locate the functional origin of DNA replication on the S. coelicolor A3(2) chromosome. This technique was used to compare the relative abundance of particular genes at different locations on the S. coelicolor chromosome in stationary-phase and rapidly growing cultures. This approach is a molecular biological analog of the genetic experiments performed by Masters and Broda (14) to demonstrate the bidirectional replication of the E. coli chromosome from a single fixed site of initiation. It is known that, in bacterial cells which are actively replicating their DNA, genes close to the replication origin will be overrepresented in comparison to those close to the terminus. This effect should be exaggerated in cells growing at, or close to, their maximum specific growth rate, when a number of rounds of chromosome replication may be proceeding at the same time (5). The gyrB gene was chosen as a probe because, in all bacterial genera examined to date, the replication origin has been found to lie within or close to the dnaA-dnaN-recF-gyrB region (16). The other five probes were chosen in order to detect genes which are widely spaced on the chromosome (11).The experiments were performed with continuous-flow cultures of S. coelicolor MT1109, an SCP1-/SCP2-derivative of the wild-type strain 1147 (7) (unpublished data); twofolddiluted Luria broth was used as the growth medium (18). Each chemostat experiment involved several shift-up steps from an initial low growth rate (dilution rate, 0.19 h-1). A steady state was established at each step, until a dilution rate just below the critical dilution rate (0.32 h-1; rate at which dilution exceeds growth) was attained. After establishment ...

SUMMARYA number of scombrotoxin poisoning incidents which have recently occurred in the UK following the consumption of canned fish have been investigated. Symptoms are described and the relationship between the histamine content of incriminated samples and toxicity is discussed.