Effects of limited feeding of aflatoxin B1 contaminated feed on the performance of broilers

The forty-two days long experiment was conducted on a total of 1000 Arbor Acres broilers, divided into two groups. Both groups of broilers were fed with a commercial feed mixture which consisted of standard feedstuffs and contained enough nutrients regarding the requirements. During the first three weeks of the trial, corn naturally contaminated with AFB₁ 0.0445 ppm per kg dry matter was used in the amount of 20% in the experimental group, while AFB₁ free corn was given to birds in the control group. After the period of toxin administration until the end of the trial, broilers from both groups were normally fed another 5 weeks with uncontaminated feed. In the first phase of the trial, broilers in the control groups had an average daily gain (ADG) of 31 g, average daily feed intake (ADFI) of 45 g and a feed: gain ratio (FCR) of 1.42. In the same time, experimental broilers achieved an ADG of 25 g, ADFI of 35 g and a FCR of 1.39. During the whole period of the trial, control and experimental broilers achieved 49.12 g, 95.24 g and 1.94 and 39.71 g, 86.90 g and 2.19, respectively.     

Heat stress in the presence of low RNA polymerase activity increases chromosome copy number of Escherichia coli

Summary A temperature shift-up accompanied by a reduction in RNA polymerase activity in Escherichia coli causes an increased rate of initiation leading to a 1.7- to 2.2-fold increase in chromosome copy number. A temperature shift-up without a reduction in polymerase activity induces only a transient non-scheduled initiation of chromosome replication caused by heat shock with no detectable effect on chromosome copy number.     

Mutagenic and clastogenic activity of nitracrine analogues in cultured V79 Chinese hamster cells

Nitracrine is used clinically as an antitumour agent, and analogues are actively being developed in some laboratories. The mutagenic activity of 9-[(3-dimethylaminopropyl)amino]-acridine and its 1-nitro (nitracrine), 2-, 3- and 4-nitro derivatives was evaluated at the 6-thioguanine and ouabain resistance loci in cultured Chinese hamster fibroblasts (V79-171b cell line). The des-nitro, 2- and 3-nitro caused no statistically significant mutagenic activity at either locus. Each of these 3 compounds weakly increased (approximately 2-fold) the incidence of micronuclei in the same cell line when tested at cytotoxic doses. Both the 1- and 4-nitro compounds increased the incidence of 6-thioguanine resistant cells from around 1 in 10(-6) to approximately 1 in 10(-4). The former compound significantly increased the frequency of ouabain-resistant cells. Both of these compounds were potent inducers of micronuclei in V79-171b cells, indicating high clastogenic activity. It would appear prudent to regard both of these compounds as potential human carcinogens.     

Dasyclads, cyclocrinitids and receptaculitids: comparative morphology and paleoecology

The cyclocrinitids are an extinct tribe of dasycladacean green algae. They were anatomically very similar to certain Recent dasyclads, even at early growth stages. The morphology and preservation of cyclocrinitids strongly suggest that they had a siphonous cellular organization with extracellular, aragonitic calcification; these features are characteristic of living dasyclads. The light surficial calcification of cyclocrinitids and other dasyclads had important paleoecological effects. It restricted them to low-energy waters, as it provided relatively little structural support. It also confined them to warm, tropical waters; they are good paleoequatorial indicators. The decline of these algae during the late Ordovician and early Silurian may therefore reflect the simultaneous cooling and glaciation. Receptaculitids are entirely unrelated organisms. Their meroms have several distinctive features; they are not homologous to the lateral branches of cyclocrinitids or dasyclads. Receptaculitid calcification was extensive and their thalli were apparently quite sturdy; they often occurred in reefs. Receptaculitids also lived in high-latitude, cold-water environments. Thus, they were ecologically unlike any calcareous green algae, and cannot be used as paleoequatorial indicators. Receptaculitids remain problematical, although the arrangement of meroms suggests plant affinities. □ Calcareous algae, Problematica, Dasycladales, Cyclocriniteae, Receptaculitales, morphology, classification, paleoecology, paleogeography .     

Biology, serology and biochemistry of leucemogenic viruses derived from a radiation-induced tumor of C57BL mice

Two distinct rat propagates of a radiation leukemia virus (RadLV-Rs) from the C57BL mouse respectively induced characteristic leukemogenic effects. These were found to be related with the infection titers of the isolates, but not with either their antigenic specificities or their viral and proviral genome sequences.