Why on Earth: Self-assembly of the first bacterial cell to abundantand diverse bacterial species

About 80% of the evolutionary history of life on Earth is restricted to microorganisms which have had several billion years to speciate. The reasons for the origin (self-assembly) of life on Earth, bacterial cell division and why there are so many different bacteria and their global dispersal are discussed from an evolutionary perspective.     

How brood influences caste aggregation patterns in the dimorphic ant species Pheidole pallidula

Spatial distribution of ant workers and, notably their aggregation/segregation behaviour, is a key-element of the colony social organization contributing to the efficiency of task performance and division of labour. In polymorphic species, specialized worker castes notably differ in their intrinsic aggregation behaviour. In this context, knowing the preponderant role of minors in brood care, we investigate how a stimulus such as brood can influence the spatial patterns of Pheidole pallidula worker castes. In a homogeneous area without brood, it was shown that minors display only a low level of aggregation while majors form large clusters in the central area. Here we find out that these aggregation patterns of both minors and majors can be deeply influenced by the presence of brood. For minors, it nucleates or enhances the formation of a large stable cluster. Such high sensitivity of minors to brood stimuli fits well with their role as main brood tenders in the colony. For majors, interattraction between individuals still remains the prevailing aggregation factor while brood strongly influences the localisation of their cluster. We discuss how the balance between interattraction and sensitivity to environmental stimuli determines the mobility of each worker castes and, consequently, the availability of minors and majors to participate in everyday colony tasks. Moreover, we will evoke the functional value of majors’ cluster location close to the brood, namely with respect to social regulation of the colony caste ratio. Received 30 May 2005; revised 11 January 2006; accepted 13 January 2006.     

Enzymatic Synthesis of Dehydro Cyclo(His–Phe)s,Analogs of the Potent Cell Cycle Inhibitor,Dehydrophenylahistin, and Their Inhibitory Activities toward Cell Division

Cyclo(His–Phe) was effectively converted to its dehydro derivatives by the enzyme of Streptomyces albulus KO-23, an albonoursin-producing actinomycete. Two types of dehydro derivatives were isolated from the reaction mixture and identified as cyclo(ΔHis–ΔPhe) and cyclo(His–ΔPhe). This is the first report on cyclo(His–ΔPhe) and the enzymatic preparation of both compounds. Cyclo(ΔHis–ΔPhe), a tetradehydro cyclic dipeptide, exhibited a minimum inhibitory concentration of 0.78 μmol/ml inhibitory activity toward the first cleavage of sea urchin embryos, in contrast to cyclo(His–ΔPhe) that had no activity. The finding that the isoprenylated derivative of cyclo(ΔHis–ΔPhe), dehydrophyenylahistin, had 2,000 times higher activity than cyclo(ΔHis–ΔPhe) indicates that an isoprenyl group attached to an imidazole ring of the compound was essential for the inhibitory activity.     

Effects of different sterols on the inhibition of cell culture growth caused by the growth retardant tetcyclacis

Cell division in cell suspension cultures can be completely blocked by the growth retardant tetcyclacis at a concentration of 10^-4 mol l^-1. In rice cells it has been demonstrated that the growth inhibition can be completely overcome by application of cholesterol independent of the duration of pretreatment with tetcyclacis. In suspension cultures of maize and soybean, too, the effect of tetcyclacis on cell division was neutralized by adding cholesterol. Other plant sterols, stigmasterol, campesterol and sitosterol were active in a decreasing order. Modifications in the cholesterol perhydro-cyclopentanophenanthrene-ring system indicate that the hydroxyl group at C-3 and the double bond between C-5 and C-6 in ring B are required for the activity. In contrast, gibberellic acid as well as ent-kaurenoic acid could not compensate retardant effects. Likewise, tetcyclasis did not change the level of gibberellins in rice cells as shown by radioimmunoassay. Thus, it is concluded that in cell suspension cultures sterols play a more important role in cell division than gibberellins.Abbreviation GA_x gibberelin A_x     

An Oscillating MinD Protein Determines the Cellular Positioning of the Motility Machinery in Archaea

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Heteropolarity in unicellular cyanobacteria: structure and development ofCyanocystis violacea

Cyanocystis violacea isolated from a marine rock sample conforms with the diagnosis ofDermocarpa violacea Crouan in all significant characteristics. The distinct heteropolarity of the cells and simultaneous cell divisions, are stable characters in culture. Development and growth of cells, simultaneous cell division and nanocyte formation have been documented by single-cell slide cultures and fine structural studies. The reddish violet color of the cytoplasm is due to the abundance of phycoerythrin.This paper is dedicated to Prof. DrLothar Geitler, whose monumental contribution to the knowledge of blue-green algae will remain the basis for future studies on these organisms for many years to come. One of us (EIF) was fortunate enough to have had Prof.Geitler as his major professor. All of us consider Prof.Geitler our teacher.     

Regulation of cell division and malignant transformation

The problem of regulation of cell division is essentially a problem of understanding regulation of transition from the resting state of a cell to the dividing state and vice versa. In malignancy the ability to revert back to a normal resting state is impaired. A model is presented which attempts to explain the control of the above transitions through control of uptake of essential nutrients by a transport-inhibitory protein. Experimental evidence in favour of the model is given.