The significance of a facultative bacterium to natural populations of the pea aphid Acyrthosiphon pisum

Abstract. 1.  Laboratory studies have implicated various accessory bacteria of aphids as important determinants of aphid performance, especially on certain plant species and under certain thermal regimes. One of these accessory bacteria is PABS (also known as T-type), which is distributed widely but is not universal in natural populations of the pea aphid Acyrthosiphon pisum in the U.K.
2.  To explore the impact of PABS on the performance of A. pisum , the nymphal development time and fecundity of aphids collected directly from natural populations and caged on the host plant Vicia faba in the field were quantified. Over 4 consecutive months June–September 1999, the performance of PABS-positive and PABS-negative aphids did not differ significantly.
3.  Deterministic modelling of the performance data showed that the variation in simulated population increase of PABS-positive and PABS-negative aphids would overlap substantially.
4.  Analysis of aphids colonising five host plants ( Lathyrus odoratus , Medicago sativa , Pisum sativum , Trifolium pratense , Vicia faba ) between April and September 2000 and 2001, identified no robust differences between the distribution of PABS-positive and PABS-negative aphids on different plants and with season or temperature.
5.  It is concluded that PABS is not an important factor shaping the performance or plant range of A. pisum under the field conditions tested. Reasons for the discrepancies between this study and laboratory-based studies are considered.     

Intergeneric and intrageneric conjugal transfer of plasmids pAMβ1, pIL205 and pIP501 in Lactobacillus sake

Abstract Three membrane-bound acid-stable cytochromes c with molecular masses of 46, 30 and 21 kDa were characterized from a new Thiobacillus ferrooxidans strain. They were solubilized with high concentrations of dodecylmaltoside at pH 8. The 30 kDa cytochrome c was purified to a homogeneous state as established by SDS-PAGE analysis. It showed an absorption peak at 410 nm in the oxidized form and at 418, 523 and 552 nm in the reduced form. The 46 kDa cytochrome c co-purified with a non-heme protein of 36 kDa. The amino acid composition and the N-terminal amino acid sequence of the 46 kDa cytochrome c were determined and compared with those of the soluble 14 kDa and the membrane-bound 21, 22.3 and 68 kDa cytochromes c isolated from two different strains. The results clearly show that this cytochrome is distinct from both the 22.3, 21 and 14 kDa cytochrome species, and exhibits some similarities with the 68 kDa cytochrome c as regards its amino acid composition.     

Effect of pea bacterial blight (Pseudomonas syringae pv. pisi) on the yield of spring sown combining peas (Pisum sativum)

Field trials to examine the effect of pea bacterial blight (Pseudomonas syringae pv. pisi) (Psp) on the yield of combining peas were carried out at five sites (HRI Wellesbourne, ADAS Rosemaund, ADAS Terrington, PGRO, SASA East Craigs) in the UK in 1990, 1991 and 1992. Healthy seed, cv. Solara, and seed naturally infected with Psp Race 2 was sown in large plots (c. 200 m²) in the open or under nets to prevent bird damage by pigeons. Despite relatively low disease severity levels (< 15% leaf area) and separation by at least 12 m of cv. Consort (resistant to Race 2) between plots there was considerable spread of disease into plots sown with healthy seed. Regression analysis demonstrated a significant relationship between yield and disease. Of the disease measurements examined, disease severity on the leaves (stipules) at growth stage 208 was found to be the best predictor of yield. A model containing environmental and bird damage terms, in addition to disease, suggested that a yield loss of 0.98 t/ha would be expected for a disease severity score of 1, equivalent to 5% leaf area affected, at growth stage 208.     

Diversity of antagonistic bacteria isolated from medicinal plant Peganum harmala L.

The antimicrobial activity of plant extract of Peganum harmala, a medicinal plant has been studied already. However, knowledge about bacterial diversity associated with different parts of host plant antagonistic to different human pathogenic bacteria is limited. In this study, bacteria were isolated from root, leaf and fruit of plant. Among 188 bacterial isolates isolated from different parts of the plant only 24 were found to be active against different pathogenic bacteria i.e. Escherichia coli, Methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecium, Enterococcus faecalis and Pseudomonas aeruginosa. These active bacterial isolates were identified on the basis of 16S rRNA gene analysis. Total population of bacteria isolated from plant was high in root, following leaf and fruit. Antagonistic bacteria were also more abundant in root as compared to leaf and fruit. Two isolates (EA5 and EA18) exhibited antagonistic activity against most of the targeted pathogenic bacteria mentioned above. Some isolates showed strong inhibition for one targeted pathogenic bacterium while weak or no inhibition for others. Most of the antagonistic isolates were active against MRSA, following E. faecium, P. aeruginosa, E. coli and E. faecalis. Taken together, our results show that medicinal plants are good source of antagonistic bacteria having inhibitory effect against clinical bacterial pathogens.     

Occurrence of two structural types of mercury reductases among Gram-positive bacteria

Structural variants of mercury reductase containing the N-terminal domain, which is easily cleaved by trypsin, have been found in Gram-positive bacteria with a low genomic G + C content (Bacillus, Staphylococcus and, possibly, some other genera). Mercury reductases without the N-terminal domain and relatively resistant to limited proteolysis are typical for Gram-positive bacteria with a high genomic G + C content (Arthrobacter, Citreobacterium, Micrococcus, Mycobacterium, Rhodococcus). Both types of mercury reductase genes may be located on plasmids.     

Phylogenetic analysis of a novel sulfate-reducing magnetic bacterium, RS-1, demonstrates its membership of the δ-Proteobacteria

Abstract Most of the 16S ribosomal RNA gene of a sulfate-reducing magnetic bacterium, RS-1, was sequenced, and phylogenetic analysis was carried out. The results suggest that RS-1 is a member of the δ-Proteobacteria, and it appears to represent a new genus. RS-1 is the first bacterium reported outside the α-Proteobacteria that contains magnetite inclusions. RS-1 therefore disrupts the correlation between the α-Proteobacteria and possession of magnetite inclusions, and that between the δ-Proteobacteria and possession of greigite inclusions. The existence of RS-1 also suggests that intracellular magnetite biomineralization is of multiple evolutionary origins.     

Bacteriolytic activities of the free-living soil amoebae,Acanthamoeba castellanii,Acanthamoeba polyphaga andHartmannella vermiformis

Bacteriolytic activities of axenically grown free-living soil amoebaeAcanthamoeba castellanii, Acanthamoeba polyphaga andHartmannella vermiformis towards various Gram-positive and Gram-negative bacteria were determined. A spectrophotometric assay revealed that the specific bacteriolytic activities of bothAcanthamoeba species were higher as those of the threeHartmannella strains.Bacillus megaterium, Bacillus subtilis, Chromatium vinosum, Micrococcus luteus andPseudomonas fluorescens were more easily lysed than the other bacteria tested.Agrobacterium tumefaciens, Klebsiella aerogenes andSerratia marcescens were hardly affected at all by the amoebal bacteriolytic activities. Among the Gram-negative bacteria we observed differences in lysis sensitivity while the Gram-positive bacteria tested were sensitive to lysis. Isoelectric focusing (IEF) gel-electrophoresis in the pH range 3–10 was performed to separate the bacteriolytic isoenzymes of amoebae. Bacteriolytic patterns were shown by using an activity assay in which lysis bands were formed in the agar/bacteria gel-overlay. The activity assay revealed remarkable differences in typical banding patterns for bacteriolytic activities among amoebae. Distinct differences between typical pI points of bacteriolytic activities inAcanthamoeba andHartmannella were shown. Bacteriolytic activities ofHartmannella were more pronounced and observed in the isoelectric points (pI) range of 4.0–9.3 while forAcanthamoeba the range was pI 4.5–8.9.Abbreviations IEF isoelectric focusing - PAA-IEF polyacrylamide-isoelectric focusing - CCAP culture collection of algae and protozoa - AS amoeba saline medium - pI isoelectric points