'Cover story': a study in land management

This article summarises an environmental research project undertaken by pupils of Mondeor High School, Johannesburg. The project was entered for the Enviro '85 Competition where it won the Civic Awareness Section and was overall winner of the competition

MUTATION CONFERRING STREPTOMYCIN RESISTANCE IN XANTHOMONAS PHASEOLI

Spontaneous mutations conferring resistance to the action of 500 to 2000 μg/ml streptomycin occur at an over-all rate of about 3 × 10−10per bacterium per generation in Xanthomonas phaseoli. Some mutants will not grow in the absence of streptomycin; others grow both in the presence and in the absence of the drug. In most cases resistance to high concentrations of streptomycin does not affect the virulence of this organism for bean plants.</jats:p

LYSOGENY IN RHIZOBIUM TRIFOLII

A phage-like particle (phage i) found in filtrates of Rhizobium trifolii (strain RT 9) did not produce plaques but induced development of two different phages in a presumed defective lysogenic strain (RT 10). These induced phages (phages 9 and 10) differed in their host ranges and produced plaques on strains RT 9 and RT 10, respectively. Phages 9 and 10 were closely related serologically and were distinct from phage i. Although ultraviolet irradiation resulted in the lysis of RT 10, no free phage was detectable in such lysates. Phage i particles had morphological, chemical, and physical properties similar to those of functional Rhizobium phages but did not produce plaques on any of 12 R. trifolii strains tested. Development of phage i could be induced with ultraviolet irradiation or by treatment with mitomycin C. </jats:p

Soil bacteria: a principal component analysis and guanine–cytosine contents of some arthrobacter–coryneform soil isolates and of some named cultures

A two-stage principal component (P.C.) procedure was applied in a comparison of the nature and properties of 19 named cultures of Arthrobacter and 77 arthrobacter–coryneform soil isolates: cultures of Brevibacterium linens, Nocardia cellulans, Corynebacterium michiganense, and Jensenia canicruria were also studied. These cultures were characterized in terms of their reaction to a set of 98 tests. Deoxyribonucleic acid (DNA) was isolated from 55 of the cultures and the moles % guanine + cytosine (% GC) content determined by thermal denaturation and ultracentrifugation methods. The P.C. analysis resulted in the recognition of 13 groups of cultures. Twelve of the Arthrobacter cultures (representing nine species) were contained in two groups, one of which contained only Arthrobacter cultures. Arthrobacter citreus, A. duodecadis, A. flavescens, and A. terregens were contained in another group with 13 soil isolates. Arthrobacter simplex and A. tumescens were located in separate groups which also included B. linens and N. cellulans respectively; otherwise these groups contained soil isolates. C. michiganense was located in a group of four soil isolates which was spatially related to the two groups of Arthrobacter cultures. Twenty-five characteristics were considered important for differentiating the groups of cultures and they were concerned with nutritional requirements, use of carbon compounds, catalase production, nitrate reduction, antibiotic sensitivity, and the Gram reaction. Most of the named Arthrobacter cultures were located in groups which were separated from the groups of the soil isolates. The DNA of the 55 cultures examined contained from 40 to 74% GC: for 32 of these cultures the GC content of DNA was between 59 and 66% and for 19 cultures the GC content was between 66 and 74%. With few exceptions cultures grouped together by the numerical method had similar GC contents. </jats:p

LYSOGENY IN A STRAIN OF XANTHOMONAS GAMPESTRIS

Fourteen bacterial strains representing eight so-called species of phytopathogenic xanthomonads were tested for lysogeny both before and after treatments known to induce phage development in lysogenic bacteria. Only a single temperate phage, of restricted host range, was found. Evidence suggestive of defective lysogeny was found in a number of cases.Strain P165, Xanthomonas campestris, when treated with antibiotic Mitomycin C at a concentration of 0.1,ug/ml in nutrient broth, produced phage particles active on strain P12S, X. campestris. No other sensitive strains were found among the 81 tested, representing 22 species of Xanthomonas. This phage (P165/P125) produced small turbid plaques, 0.6 mm to 0.8 mm in diameter, with indefinite margins. Evidence for the lysogenization of P125 strain by this phage was found. Clear plaques were sometimes found in lawns of lysogenized cells of P12S. These were presumably derived from phage mutants with increased virulence. When examined under the electron microscope, the phage particles were semispherical, approximately 65 m/x in diameter with rudimentary tails.</jats:p