Composition of Acridid gut bacterial communities as revealed by 16S rRNA gene analysis.

The gut bacterial community from four species of feral locusts and grasshoppers was determined by denaturing gradient gel electrophoresis (DGGE) analysis of bacterial 16S rRNA gene fragments. The study revealed an effect of phase polymorphism on gut bacterial diversity in brown locusts from South Africa. A single bacterial phylotype, consistent with Citrobacter sp. dominated the gut microbiota of two sympatric populations of Moroccan and Italian locusts in Spain. There was evidence for Wollbachia sp. in the meadow grasshopper caught locally in the UK. Sequence analysis of DGGE products did not reveal evidence for unculturable bacteria and homologies suggested that bacterial species were principally Gammaproteobacteria from the family Enterobacteriaceae similar to those recorded previously in laboratory reared locusts.

The gut bacteria of insects: nonpathogenic interactions.

The diversity of the Insecta is reflected in the large and varied microbial communities inhabiting the gut. Studies, particularly with termites and cockroaches, have focused on the nutritional contributions of gut bacteria in insects living on suboptimal diets. The indigenous gut bacteria, however, also play a role in withstanding the colonization of the gut by non-indigenous species including pathogens. Gut bacterial consortia adapt by the transfer of plasmids and transconjugation between bacterial strains, and some insect species provide ideal conditions for bacterial conjugation, which suggests that the gut is a "hot spot" for gene transfer. Genomic analysis provides new avenues for the study of the gut microbial community and will reveal the molecular foundations of the relationships between the insect and its microbiome. In this review the intestinal bacteria is discussed in the context of developing our understanding of symbiotic relationships, of multitrophic interactions between insects and plant or animal host, and in developing new strategies for controlling insect pests.

An indigo-reducing moderate thermophile from a woad vat, Clostridium isatidis sp. nov.

A Gram-positive, anaerobic, moderate thermophile, strain Wv6T, capable of reducing indigo dye, was isolated from a fermenting woad vat prepared essentially as in medieval Europe. Strain Wv6T formed rod-shaped cells, which occurred singly, in pairs or in chains and produced terminal oval endospores. Strain Wv6T was saccharolytic. Growth occurred at pH 5.9-9.9 (initial pH) with an optimum at 50 degrees C of pH 7.2 +/- 0.2 (constant pH). At pH 7.8, the temperature range for growth was 30-55 degrees C with the optimum at 49-52 degrees C. Comparative 16S rRNA gene sequence analysis demonstrated that the bacterium represents a hitherto unknown subline within rRNA cluster I Clostridium. Based on the results of the phylogenetic analysis and phenotypic criteria, it is proposed that the unknown moderate thermophile should be classified as Clostridium isatidis sp. nov., a new species of the genus Clostridium. The type strain of Clostridium isatidis is strain Wv6T (= NCFB 3071T).

Assessment of cyanogenic glucoside (cyanide) residues in Mbege: an opaque traditional Tanzanian beer.

Levels of cyanide in two varieties of malted millet, spent grain (Machicha) and opaque beer (Mbege) were determined. Protein content and amino acid composition of the malt, Mbege and Machicha were determined. Mbege was made in the laboratory using an improved method. The cyanide content of millet, malt, spent grain and Mbege were 40.6, 513.4, 18.9 and 8.1 ppm, respectively for the Moshi local millet variety. For Sumbawanga-2 millet variety the cyanide content was found to be 41.2, 489.2, 17.8 and 6.8 ppm for the millet, malt, spent grain and Mbege, respectively. The cyanide content increased linearly as the number of days of germination of the millet grain increased and the highest values of cyanide were attained on the third day of germination. Cyanogenic glucosides in the millet were enzymetically hydrolysed to respective cyanohydrins and volatile hydrogen cyanide due to low pH level of the Mbege which was 4. Malting of the millet increased the protein content by 5%. Lysine, the most limiting amino acid in millet, increased by 20%. It was concluded that the fermentation process of the millet malt into Mbege is efficient in reducing the levels of cyanogenic glucosides below levels considered toxic and therefore rendering the product safe.

Munkoyo beverage, a traditional Zambian fermented maize gruel using Rhynchosia root as amylase source.

A typical munkoyo beverage was made by fermenting Rhynchosia heterophylla root extract-cooked maize meal mixture with Lactobacillus confusus LZI and Saccharomyces cerevisiae YZ20. The fermented munkoyo beverage had a pH of 3.3, lactic acid content of 60 mmol/l, ethanol 320-410 mmol/l and a characteristic 'munkoyo' aroma. L. confusus, used alone, produced a beverage with a faint munkoyo flavour note whilst beverage produced with S. cerevisiae alone seemed not to have a typical munkoyo note. R. heterophylla root extract converted 75% of the starch in sterile cooked maize meat to maltose (80% of total sugars), maltotriose (17%) and glucose (3%) in I h at 45 degrees C. During fermentation by the mixed culture or the yeast alone most of the maltose was utilised but little or none of the maltotriose. The ratio of yeast to lactic acid bacteria in the starter culture affected the rate of production of ethanol but had no effect on the growth or acid production by the bacterium. To obtain a munkoyo beverage with the desired low alcohol concentration (< 100 mmol/l), the ratio of yeast concentration (cfu/ml) to Lactobacillus concentration in the starter culture should be 1:1000 or less and the beverage should be fermented for 24 h only.

A study of sulfite-tolerant yeasts from comminuted lamb products.

The sulfite tolerance of meat yeasts was shown to be determined by pH, sulfite concentration, substrate availability, and the composition of the preincubation medium. Acetaldehyde production by Candida norvegica was sulfite-induced and occurred during the exponential growth phase in sulfited (500 micrograms SO2 ml-1) lab lemco glucose broth cultures buffered at pH 5, 6, or 7. Growth at pH 4, however, was inhibited by sulfite. Acetaldehyde production occurred in sulfited medium containing fructose or ethanol but not lactate nor a range of other assimilable substrates. A non-acetaldehyde-producing yeast, Candida vini, grew in sulfited (500 micrograms SO2 ml-1) lab lemco broth containing glucose or lactate buffered at pH 6 or 7 but not at pH 4 or 5.

Glucose, the key substrate in the microbiological changes occurring in meat and certain meat products.

The literature dealing with the role of glucose in the microbiological changes of meat and certain meat products is reviewed. Discussion is centered on two aspects. First, glucose plays a part in the selection of the dominant spoilage organisms, Pseudomonas fragi, Ps. lundensis, and Ps. fluorescens, on red meat stored aerobically under chill (2-7 degrees C) conditions. It is concluded that the pseudomonads flourish because they convert glucose to the less commonly used substrate, gluconate. The latter serves as an extracellular energy store. With its depletion, the pseudomonads utilize amino acids, thereby producing the characteristic off-odors of spoiled meat. Storage of meat in a modified atmosphere (viz., 20% CO2:80% O2) selects Gram-positive flora (lactobacilli and Brochothrix thermosphacta) which impart a "cheesy odor" through acid production from glucose and volatile fatty acids from amino acids. The first mentioned organisms produce the same off-odors in "acid" meat (pH 5.5) from which oxygen is excluded. So too does the less acid-tolerant Br. thermosphacta in less acid meat (pH greater than 5.8), especially if trace amounts of O2 are present. Such meat may be colonized by Shewanella putrefaciens also, with green discoloration resulting from the release of H2S from amino acids. The addition of glucose and NO2- to, and the exclusion of oxygen from, comminuted meat selects a flora dominated by Lactobacillus spp. and staphylococci such as Staphylococcus carnosus. Second, sulfite, the preservative of British-style sausages, has a sparing action on glucose. As a consequence of its curtailed breakdown there is only a meager acid drift with storage even though a fermentative flora of lactobacilli and Br. thermosphacta is selected. Yeasts also contribute to the microbial association in sausages; members of four of the six commonly occurring genera bind sulfite through acetaldehyde production. Glucose appears to be essential for acetaldehyde synthesis. The role of glucose in spoilage and the conditions which select particular groups of spoilage organisms are considered in the context of chemical probes and/or instrumental methods for routine assessment of the "freshness" of meat and meat products.