Susceptibility of Agrobacterium tumefaciens Strains to Two Agrocin-Producing Agrobacterium Strains

Sixty-five strains and isolates of Agrobacterium tumefaciens representing each of the known biotypes, were tested for in vitro and in vivo susceptibility to the agrocin-producing strains Agrobacterium radiobacter 84 and A. tumefaciens D286. No biotype 3 strain was susceptible to the effects of either of the agrocinogenic strains in vitro. On datura and tobacco, the best inhibition of tumor formation was obtained when the agrocinogenic strains were applied to wounds 24 h before the pathogens and by the concomitant application of agrocin producer and pathogen at cell ratios of 10:1 or 3:1; inhibition of infection tended to decrease progressively as the cell ratio decreased from 10:1 to 3:1 to 1:1. Generally, strain 84 was superior to D286 in inhibiting tumor formation. A combined cell suspension of 84 and D286 was as effective as 84 alone. The overall pattern of inhibition of tumor formation by biotype 1 and 2 pathogens resistant to the agrocinogenic strains in vitro was similar to that obtained with strains that were susceptible in vitro.     

Emergence of Novel Streptococcus iniae Exopolysaccharide-Producing Strains following Vaccination with Nonproducing Strains

Streptococcus iniae is a major pathogen of fish, producing fatal disease among fish species living in very diverse environments. Recently, reoccurrences of disease outbreaks were recorded in rainbow trout (Oncorhynchus mykiss, Walbaum) farms where the entire fish population was routinely vaccinated. New strains are distinguished from previous strains by their ability to produce large amounts of extracellular polysaccharide that is released into the medium. Present findings indicate that the extracellular polysaccharide is a major antigenic factor, suggesting an evolutionary selection of strains capable of extracellular polysaccharide production.     

Influence of Azospirillum Strains on the Nodulation of Clovers by Rhizobium Strains

Mixed cultures of several Azospirillum and Rhizobium trifolii strains caused either an inhibition or stimulation of nodule formation on plant hosts as compared with nodulation of plants inoculated with R. trifolii alone. Azospirillum strains affected the nodulation process at a precise cell ratio (R. trifolii/Azospirillum cells) and time of inoculation. All Azospirillum strains used showed a variation in their ability to inhibit or enhance nodulation by R. trifolii strains. When nonviable cell preparations of Azospirillum strains were used for mixing experiments, no effect on nodulation was observed. A decrease in the effectiveness of normally Nod⁺ Fix⁺R. trifolii strains was observed when an Azospirillum strain caused an increase in nodule number.     

Deoxyribonuclease-Positive Staphylococcus epidermidis Strains

Use of the agar plate test for the enzyme deoxyribonucleate 3′-nucleotidohydrolase (deoxyribonuclease) can result in frequent misdiagnosis of Staphylococcus epidermidis as S. aureus.     

火菇属野生菌株发酵液对栽培菌株的化感效应

为探究火菇属Flammulina野生菌株发酵液对栽培菌株的影响,以火菇属野生柳生金针菇F. rossica F52、野生金针菇F. filiformis F39和栽培金针菇F. filiformis F47为供试菌株,采用固体平板培养和液体发酵的方法,对比了添加不同体积分数火菇属野生菌株发酵液对栽培菌株平板中菌丝长速、液体发酵中菌丝生物量、干质量及漆酶和淀粉酶活力的影响。结果表明：不同体积分数野生金针菇菌株F39发酵液对栽培菌株F47菌丝长速有抑制作用,对发酵液中菌丝生物量无显著影响,当添加发酵液体积分数为50%时可显著提高菌株F47发酵液中漆酶活力,当体积分数为40%时,可显著提高菌株F47发酵液中淀粉酶的活力（P<0.05）;添加不同体积分数的野生柳生金针菇菌株F52发酵液对菌株F47除淀粉酶外其他指标均影响显著,添加体积分数为30%的发酵液对栽培金针菇F47菌丝长速具有显著的促进作用,当添加发酵液体积分数为40%时,对菌株F47液体发酵中菌丝干质量和漆酶活力均有显著促进作用（P<0.05）。证明了化感效应不仅存在于属间,在同属下的种间也存在。     

The Ah Phenotype. Survey of Forty-Eight Rat Strains and Twenty Inbred Mouse Strains

Forty-four inbred and four randombred rat strains and 20 inbred mouse strains were examined for their Ah phenotype by determining the induction of liver microsomal aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity (EC 1.14.14.1) by intraperitoneal treatment with either β-naphthoflavone or 3-methylcholanthrene. All 48 rat strains were found to be Ah-responsive. The maximally induced hydroxylase specific activities of the ALB/Pit, MNR/Pit, MR/Pit, SHR/Pit, and Sprague-Dawley strains were of the same order of magnitude as the basal hydroxylase specific activities of the ACI/Pit, F344/Pit, OKA/Pit, and MNR/N strains. Six of the 20 mouse strains were Ah-nonresponsive (i.e. lacking the normal induction response and presumably lacking detectable amounts of the Ah receptor). The basal hydroxylase specific activities of the BDL/N, NFS/N, STAR/N, and ST/JN mouse strains were more than twice as high as the maximally induced hydroxylase specific activity of the CBA/HT strain.——To date, 24 Ah-nonresponsive mouse strains have been identified, out of a total of 68 known to have been characterized. The reasons for not finding a single Ah-nonresponsive inbred rat strain—as compared with about one Ah-nonresponsive inbred mouse strain found for every three examined—remain unknown.     

Melanin Production by Rhizobium Strains

Different Rhizobium and Bradyrhizobium strains were screened for their ability to produce melanin. Pigment producers (Mel⁺) were found among strains of R. leguminosarum biovars viceae, trifolii, and phaseoli, R. meliloti, and R. fredii; none of 19 Bradyrhizobium strains examined gave a positive response. Melanin production and nod genes were plasmid borne in R. leguminosarum biovar trifolii RS24. In R. leguminosarum biovar phaseoli CFN42 and R. meliloti GR015, mel genes were located in the respective symbiotic plasmids. In R. fredii USDA 205, melanin production correlated with the presence of its smallest indigenous plasmid.     

两株蛋白酶产生菌的分类鉴定

前期试验筛选出两株具有产蛋白酶能力的菌株H1和H2。通过形态学观察及生理生化特征实验对这两株微生物进行了鉴定,初步确定H1属于短杆菌属(Brevibacterium),H2属于葡萄球菌属(Staphylococcus)。进一步测定了两株蛋白酶产生菌的产蛋白酶能力。H1在25℃条件下酶活为每毫升566 U,H2在25℃条件下酶活为每毫升628 U。     

Colony Dimorphism in Bradyrhizobium Strains

Ten isolates of Bradyrhizobium spp. which form two colony types were studied; the isolates originated from a range of legume species. The two colony types differed in the amount of gum formed or size or both, depending on the strain. Whole 7-day-old colonies of each type were subcultured to determine the proportion of cells which had changed to the other type. An iterative computerized procedure was used to determine the rate of switching per generation between the two types and to predict proportions reached at equilibrium for each strain. The predicted proportions of the wetter (more gummy) or larger colony type at equilibrium differed significantly between strains, ranging from 0.9999 (strain CIAT 2383) to 0.0216 (strain CIAT 2469), because some strains switched faster from dry to wet (or small to large) and others switched faster from wet to dry (or large to small). Predicted equilibrium was reached after about 140 generations in strain USDA 76. In all but one strain (CIAT 3030) the growth rate of the wetter colony type was greater than or similar to that of the drier type. The mean difference in generation time between the two colony types was 0.37 h. Doubling times calculated for either colony type after 7 days of growth on the agar surface ranged from 6.0 to 7.3 h. The formation of two persistent colony types by one strain (clonal or colony dimorphism) may be a common phenomenon among Bradyrhizobium strains.     

Physiological Characterizations of Acanthamoeba Strains

ABSTRACT. Thirty-seven strains of Acanthamoeba are described using 69 physiological characters. The characterizations of the strains are based on quantitative estimates of growth responses which were standardized to eliminate any effects of differences in growth rates of the strains. Thirty-six distinct patterns are generated using numerical profiles, but it is possible to distinguish within this total diversity 20 sub-generic groups which, although not completely congruent with the morphological species, are consistent with other non-morphological characters. Evidence is presented that Acanthamoeba is a coherent, well-founded genus, but it is not desirable to recognize formal taxa at the sub-generic level.     

Freeze-drying Various Strains of Shigella

Of six candidate strains of Shigella prepared in Brain Heart Infusion broth as freeze-dried vaccine, low survival rates were obtained with two of the most promising strains. Survival rates with these two strains were increased to acceptable levels when the organisms were suspended in a medium consisting of 8.2% sucrose, 0.01 M phosphate, 0.07% monosodium glutamate, and 2.5% human serum albumin. Alteration of the freezing temperature did not improve the recovery rates significantly.     

Gas-Vacuolated Strains of Microcyclus aquaticus

Two strains of gas-vacuolated heterotrophic bacteria have been isolated from freshwaters by using 0.01% peptone enrichments. Both are nonmotile, vibrioid organisms that form rings before division. In terms of these morphological traits and other characteristics, including nutritional characters and deoxyribonucleic acid base composition, these new isolates are very similar to Microcyclus aquaticus. It is proposed that they be considered strains of this species.     

Strains overproducing tRNA for histidine

Summary Hybridization analysis of total genomic DNA indicated that Escherichia coli K12 contains a single copy of the gene encoding the histidine-accepting tRNA. This gene was subcloned onto an inducible expression vector under the control of the tac promoter. Strains carrying the resulting plasmid showed five- to six-fold increased histidine-accepting activity after induction. This overproduction of tRNA^His did not effect the growth rate of the strain or lead to derepression of the histidine biosynthetic enzymes. Neither did it have an effect on mistranslation elicited by histidine starvation. However, in cells starved for histidine by the addition of -methyl histidine, the overproduction of tRNA^His interfered with the ability of the cells to recover from starvation.