We have studied 15 gene loci coding for enzymes in 121 Trypanosoma cruzi stocks from a wide geographic range-from the United States and Mexico to Chile and southern Brazil. T. cruzi is diploid but reproduction is basically clonal, with very little if any sexuality remaining at present. We have identified 43 different clones by their genetic composition; the same genetic clone is often found in very distant places and in diverse hosts. There is much genetic heterogeneity among the different clones, and they cannot be readily classified into a few discrete groups that might represent natural taxa. These findings imply that the biological and medical characteristics need to be ascertained separately for each natural clone. The evidence indicates that clonal evolution is very ancient in T. cruzi. We propose two alternative hypotheses concerning the relationship between the biochemical diversity and the heterogeneity in other biological and medical characteristics of T. cruzi. One hypothesis is that the degree of diversity between strains simply reflects the time elapsed since their last common ancestor. The second hypothesis is that biological and medical heterogeneity is recent and reflects adaptation to different transmission cycles. A decision between the two hypotheses can be reached with appropriate studies, with important medical consequences.Isozyme studies of Trypanosoma cruzi, the causative agent of Chagas disease, were initiated in 1974 (1). Analysis of the zymograms revealed substantial isozymic variability among stocks (2-7), which were classified into three groups or "zymodemes" (2,3,8).We studied T. cruzi from Bolivian populations and proposed a genetic interpretation of the zymograms that lead to the following hypotheses. (i) T. cruzi is a diploid organism (9, 10), a conclusion supported by a DNA study (11).(ii) Mendelian sexuality is absent or very rare (10,12,13 115The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Background: Streptococcus uberis, a Gram positive bacterial pathogen responsible for a significant proportion of bovine mastitis in commercial dairy herds, colonises multiple body sites of the cow including the gut, genital tract and mammary gland. Comparative analysis of the complete genome sequence of S. uberis strain 0140J was undertaken to help elucidate the biology of this effective bovine pathogen.

Pasteurella multocida toxin (PMT) is a potent mitogen that also affects bone resorption. PMT acts intracellularly and is therefore postulated to have several domains involved in different aspects of its function. The toxin contains eight cysteine residues. Mutants with individual substitutions for each of these residues were constructed, and the effects of these on the biological activity of the toxin were determined by cultured-cell assays. Only the most C-terminal of the eight cysteines (C1165) was essential for full activity, although mutation of the cysteine residue at position 1159 caused a slight but reproducible loss of potency. In animal challenge experiments, mutant toxin (C1165S) was not toxic to piglets, even at doses exceeding a lethal dose of active PMT 1,000-fold. The mutant and wild-type toxins displayed identical purification characteristics, similar susceptibility to proteolytic digestion, and circular dichroism profiles, which indicated that no gross structural changes had taken place. The function of the essential C1165 residue is not yet known, although its most likely role is an enzymatic one at or near the catalytic center of the toxin.

The SARS-CoV-2 virus is more transmissible than previous coronaviruses and causes a more serious illness than seasonal flu. The SARS-CoV-2 receptor binding domain (RBD) of the Spike protein binds to the human angiotensin-converting enzyme 2 (ACE2) receptor as a prelude to viral entry into the cell. Using a naïve llama single chain nanobody library and PCR maturation we have produced a nanobody, H11-D4, with a KD 9 nM for RBD that blocks the binding of RBD to the ACE2. Single particle cryo-electron microscopy revealed that H11-D4 binds to each of the three RBDs in the Spike trimer. The 1.8 Å crystal structure of the H11-D4 – RBD complex has illuminated the molecular interactions that drive the high affinity. H11-D4 binds to an epitope on RBD that overlaps with the ACE2 binding, explaining the blocking of ACE2 binding. The nanobody showed potent neutralising activity against live SARS-CoV-2 virus.