Methods for rapid screening and isolation of bacteria producing acidic lipase: feasibility studies and novel activity assay protocols

Acidic lipase finds its commercial values in medical applications and bioremediation of food wastes. In this work, approaches for rapid screening of lipase-producing bacteria were developed and the feasibility assessment of the screening methods was performed. From food waste samples, the proposed screening procedures allowed isolation of sixteen pure bacterial strains expressing higher lipase activity at acidic pH (pH 6.0) than at alkaline pH (pH 9.0). To enhance the accuracy of lipase activity determination under acidic conditions, a novel assay procedure was also developed by deactivating lipase activity by microwave treatment prior to back titration. This additional step could minimize interferences arising from residual lipase activity during conventional direct back-titration methods in measuring lipase activity at acidic pH. Using the four strategies proposed in this work, the best acidic-lipase-producing isolate was obtained by strategy C (SSC) and was identified as Aeromonas sp. C14, displaying an optimal lipase activity of 0.7 U/ml at an acidic pH of 6.0.     

Plato and Peirce on Likeness and Semblance

In his well-known essay, ??What Is a Sign???(CP 2.281, 285) Peirce uses ??likeness?? and ??resemblance?? interchangeably in his definition of icon. The synonymity of the two words has rarely, if ever, been questioned. Curiously, a locus classicus of the pair, at least in F. M. Cornford??s English translation, can be found in a late dialogue of Plato, namely, the Sophist. In this dialogue on the myth and truth of the sophists?? profession, the mysterious ??stranger??, who is most likely Socrates?? persona, makes the famous distinction between eikon (likeness) and phantasma (semblance) (236a,b). For all his broad knowledge in ancient philosophy, Peirce never mentioned this parallel; nor has any Peircean scholar identified it. There seems to be little problem with eikon as likeness, but phantasma may give rise to a puzzle which this paper will attempt to solve. Plato uses two pairs of words: what eikon is to phantasma is eikastikén (the making of likeness [235d]) to phantastikén (semblance making [236c]). In other words, icons come into being because of the act of icon-making, which is none other than indexicality. Witness what Peirce says about the relationship between photographs and the objects they represent: ??But this resemblance is due to the photographs having been produced under such circumstances that they were physically forced to correspond point by point to nature.?? (Ibid.) Thus the iconicity which links the representamen (sign) and its object is made possible not only by an interpretant, but also by idexisation. Their possible etymological and epistemological links aside, the Peircean example of photographing and the Platonic discussion of painting and sculpturing in the Sophist, clearly show the physio-pragmatic aspect of iconicity. The paper will therefore reread the Peircean iconicity by closely analysing this relatively obscure Platonic text, and by so doing restore to the text its hidden semiotic dimension.     

The BNIP-2 and Cdc42GAP Homology (BCH) Domain of p50RhoGAP/Cdc42GAP Sequesters RhoA from Inactivation by the Adjacent GTPase-activating Protein Domain

The BNIP-2 and Cdc42GAP homology (BCH) domain is a novel regulator for Rho GTPases, but its impact on p50-Rho GTPase-activating protein (p50RhoGAP or Cdc42GAP) in cells remains elusive. Here we show that deletion of the BCH domain from p50RhoGAP enhanced its GAP activity and caused drastic cell rounding. Introducing constitutively active RhoA or inactivating GAP domain blocked such effect, whereas replacing the BCH domain with endosome-targeting SNX3 excluded requirement of endosomal localization in regulating the GAP activity. Substitution with homologous BCH domain from Schizosaccharomyces pombe, which does not bind mammalian RhoA, also led to complete loss of suppression. Interestingly, the p50RhoGAP BCH domain only targeted RhoA, but not Cdc42 or Rac1, and it was unable to distinguish between GDP and the GTP-bound form of RhoA. Further mutagenesis revealed a RhoA-binding motif (residues 85-120), which when deleted, significantly reduced BCH inhibition on GAP-mediated cell rounding, whereas its full suppression also required an intramolecular interaction motif (residues 169-197). Therefore, BCH domain serves as a local modulator in cis to sequester RhoA from inactivation by the adjacent GAP domain, adding to a new paradigm for regulating p50RhoGAP signaling.     

T-independent but not T-dependent antigens maintain surface Ig of lymphocytes.

The effect of T-independent (TIA) and T-dependent (IDA) antigens on the surface Ig of 24-hr cultured rabbit spleen cells was investigated by two techniques: the proportion of cells bearing surface Ig was determined by direct rosette formation with anti-light chain allotype-coated erythrocytes; the total amount of surface Ig was estimated by labeling the cells with anti-allotype ¹²⁵I-labeled Fab fragments. The addition of TIA resulted in the maintenance of the proportion of Ig-bearing cells almost to the initial level, an effect which could not be obtained with any of the TDA tested. The same type of effect was observed when the total amount of surface Ig was measured, i.e., there was a slight reduction (about 24%) in the amount of surface Ig in cultures to which TIAs were added and an almost sixfold reduction (about 70%) in cultures to which TDA, Con A, or no antigen was added. Some but not all of the TIA were able to induce [³H]TdR incorporation in 3-day spleen-cell cultures. We concluded that the common feature of TIA is the ability to stimulate the turnover of B-cell surface Ig, a feature that can be used for an easy screening of TIA.