Information spiraling: Movement of bacteria and their genes in streams

Bacteria in transport in streams are largely derived from other parts of the ecosystem. Here we review factors that influence transport of bacteria and their movement between habitats (such as sediment, water column, rocks, wood, and leaves) and consider the role of these movements in ecosystem processes. Bacteria enter the water column by sloughing, scouring, as a consequence of changes in morphology or hydrophobicity, or dislodgment by invertebrates and fish or other aquatic vertebrates. Transported cells (which may be planktonic or particle-associated) that colonize surfaces may establish new gene pools through cell division (vertical transfer) or genetic exchange (lateral transfer). Genetic information is also transported in streams as free or protected DNA or in bacteriophages. Movement of these vectors causes genetic information to spiral along a stream in a manner analogous to that of nutrients and organic carbon. Spiraling refers to the pattern of transport, uptake or attachment, and release of a molecule or cell. The flow of water in streams causes this cycle of attachment and release to be displaced downstream resulting in a spiral rather than a closed, stationary loop. Offprint requests to: L. G. Leff.     

Interaction between T cell receptor beta chain and immunoglobulin heavy chain region genes in susceptibility to insulin-dependent diabetes mellitus.

Despite some reports of an association between insulin-dependent diabetes mellitus (IDDM) and a BglII RFLP in the T cell receptor beta chain (TCRB) constant region, results of several recent studies, including our own, have failed to support such an association. However, we here report evidence for an IDDM-TCRB relationship which is dependent on immunoglobulin heavy-chain-region genes. We analyzed 198 unrelated diabetics and 84 normal siblings (maximum one sibling per diabetic) typed for the BglII TCRB RFLP and Gm immunoglobulin allotypes Glm(1), Glm(2), G2m(23), and G3m(5), which identify the four common Gm haplotypes. The BglIII TCRB genotype frequencies were significantly different between diabetics positive and negative for G2m(23) (P = .017) and G3m(5) (P = .021) but were not different between normal siblings positive and negative for those allotypes (P = .94 and P = .77, respectively). Thus, there were significant interactions between TCRB, Gm, and IDDM for two of the four immunoglobulin allotypes examined. We have previously reported interactions between HLA, Gm (particularly G2m(23)), and IDDM and postulate that the TCRB-Gm-IDDM and HLA-Gm-IDDM interaction effects may be functionally related.     

Triazole-linked transition state analogs as selective inhibitors against V. cholerae sialidase

Sialidases or neuraminidases are enzymes that catalyze the cleavage of terminal sialic acids from oligosaccharides and glycoconjugates. They play important roles in bacterial and viral infection and have been attractive targets for drug development. Structure-based drug design has led to potent inhibitors against neuraminidases of influenza A viruses that have been used successfully as approved therapeutics. However, selective and effective inhibitors against bacterial and human sialidases are still being actively pursued. Guided by crystal structural analysis, several derivatives of 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (Neu5Ac2en or DANA) were designed and synthesized as triazole-linked transition state analogs. Inhibition studies revealed that glycopeptide analog E-(TriazoleNeu5Ac2en)-AKE and compound (TriazoleNeu5Ac2en)-A were selective inhibitors against Vibrio cholerae sialidase, while glycopeptide analog (TriazoleNeu5Ac2en)-AdE selectively inhibited Vibrio cholerae and A. ureafaciens sialidases.     

The relative importance of refugia in determining the drift and habitat selection of predaceous stoneflies in a sandy-bottomed stream

Patch structure in sandy, compared to rocky streams, is characterized by isolated snags that can only be colonized by drifting. By measuring drift from patches (snags) of various quality we determined the factors that influence habitat selection and drift of the predaceous stoneflies Acroneuria abnormis and Paragnetina fumosa. The presence of refugia (loose bark and leaf packs) was more important than hunger level and modified the effects of increased predator densities and aggressive interactions. Stoneflies concentrated to 8x natural densities with access to refugia remained longer on snags than a single stonefly without access to refugia. During periods of activity, refugia were defended with larger stoneflies always displacing smaller nymphs. During long periods of inactivity, two and sometimes three nymphs would rest side-by-side sharing the same refuge. Hunger level (starved versus satiated stoneflies), an indirect measure of a predator's response to prey availability, had no significant effect on drift or habitat selection regardless of the presence of refugia. Stonefly predators had a uniform distribution while their prey were clumped. Drift was deliberate and almost always delayed until night, usually at dusk or dawn. An examination of previous research plus the results of this study suggest that non-predatory intra- and interspecific interactions can be an important mechanism causing drift in streams.     

Gene duplication and divergence produce divergent MHC genotypes without disassortative mating

Genes of the major histocompatibility complex (MHC) exhibit heterozygote advantage in immune defence, which in turn can select for MHC‐disassortative mate choice. However, many species lack this expected pattern of MHC‐disassortative mating. A possible explanation lies in evolutionary processes following gene duplication: if two duplicated MHC genes become functionally diverged from each other, offspring will inherit diverse multilocus genotypes even under random mating. We used locus‐specific primers for high‐throughput sequencing of two expressed MHC Class II B genes in Leach's storm‐petrels, Oceanodroma leucorhoa, and found that exon 2 alleles fall into two gene‐specific monophyletic clades. We tested for disassortative vs. random mating at these two functionally diverged Class II B genes, using multiple metrics and different subsets of exon 2 sequence data. With good statistical power, we consistently found random assortment of mates at MHC. Despite random mating, birds had MHC genotypes with functionally diverged alleles, averaging 13 amino acid differences in pairwise comparisons of exon 2 alleles within individuals. To test whether this high MHC diversity in individuals is driven by evolutionary divergence of the two duplicated genes, we built a phylogenetic permutation model. The model showed that genotypic diversity was strongly impacted by sequence divergence between the most common allele of each gene, with a smaller additional impact of monophyly of the two genes. Divergence of allele sequences between genes may have reduced the benefits of actively seeking MHC‐dissimilar mates, in which case the evolutionary history of duplicated genes is shaping the adaptive landscape of sexual selection.     

Interactions between fire and introduced deer herbivory on coastal heath vegetation

The coastal heathlands of the Royal National Park are impacted by both fire and herbivory by introduced deer, and to date these two factors have been dealt with independently in the management of natural areas. In recent years, there has been increasing recognition for a more integrated approach to manage these two disturbance agents. Fire and its role in Australian heathlands are well known, while impacts from introduced deer and the combined effects of fire and introduced deer are still poorly understood. In this study, we investigated the effects of fire and Javan rusa deer (Cervus timorensis) on both vegetation cover and floristics. The percentage cover of plants at different height layers and the presence/absence of individual species were recorded at sites representing two different burn histories (1993/1994 and 2000/2001) and deer presence or absence. Fire significantly reduced vegetation cover at low (<50 cm) and intermediate heights (50–100 cm), while deer presence affected grasses and sedges, and low vegetation at more recently burnt sites. Rusa deer also affected composition of the plant species assemblages, but no such effect was found for fire. Understanding the influence of each disturbance factor independently and together in the heathlands will be critical for implementing a more robust framework for future management.     

Immunocompetent cells in the chicken. II. Synergism between thymus cells and either bursa or bone marrow cells in the humoral immune response to sheep erythrocytes

Newly hatched F₁ hybrid chicks isogenic for the strong B histocompatibility locus were rendered immunologically incompetent by cyclophosphamide treatment and x-irradiation. They were then injected intravenously with thymus, bone marrow, or bursa cells together with sheep erythrocytes (SE) and received another iv injection of SE 3 days later. Splenic plaque-forming cells (PFC) and serum hemagglutinins were assayed 7 days after transfer. At donor ages of 14–26 days, cells from thymus (T) and bone marrow (BM) showed synergism when injected together, as indicated by a significantly higher geometric mean of PFC per recipient spleen in the BM + T group than in the BM group. The response of the T group was extremely low. With thymus and bursa cells from 6- to 28-day-old donors, significant synergism was demonstrated in 3 of 9 individual experiments. However, almost all the other 6 experiments showed marked differences in the same direction, and the combined probability for all experiments was < 0.001. The most striking demonstration of thymus + bursa synergism was made in 2 experiments using 1-week-old donors. Bone marrow cells from 1-week-old donors failed to cooperate with thymus, as did BM cells from older bursectomized agammaglobulinemic donors. This suggests that B cells from bone marrow originate in the bursa. Thymus-bursa cooperation was somewhat difficult to demonstrate in individual experiments using donors over 1 week of age, owing to the occurrence of some responses with bursal cells alone and to variability of response within bursa or bursa + thymus recipient groups. Synergism between thymus and bursa cells was more consistently demonstrable when irradiated normal spleen or low doses of bone marrow cells were added. These additions led to an increased response and a lowered coefficient of variation in the thymus + bursa recipient groups. The ‘third’ cell type needed for optimal response by the thymus and bursa cells together was tentatively identified as a macrophage.