Soil microbial biomass and community composition along an anthropogenic disturbance gradient within a long-leaf pine habitat

Some of the finest surviving natural habitat in the United States is on military reservations where land has been protected from development. However, responsibilities of military training often require disturbance of that habitat. Herein, we show how the soil microbial community of a long-leaf pine ecosystem at Fort Benning, Georgia responds to military traffic disturbances. Using the soil microbial biomass and community composition as ecological indicators, reproducible changes showed increasing traffic disturbance decreases soil viable biomass, biomarkers for microeukaryotes and Gram-negative bacteria, while increasing the proportions of aerobic Gram-positive bacterial and Actinomycete biomarkers. Soil samples were obtained from four levels of military traffic (reference, light, moderate, and heavy) with an additional set of samples taken from previously damaged areas that were remediated via planting of trees and ground cover. Utilizing 17 phospholipid fatty acid (PLFA) variables that differed significantly with land usage, a linear discriminant analysis with cross-validation classified the four groups. Wilks’ lambda for the model was 0.032 (P<0.001). Overall, the correct classifications of profiles was 66% (compared to the chance that 25% would be correctly classified). Using this model, 10 observations taken from the remediated transects were classified. One observation was classified as a reference, three as light trafficked, and six as moderately trafficked. Non-linear artificial neural network (ANN) discriminant analysis was performed using the biomass estimates and all of the 61 PLFA variables. The resulting optimal ANN included five hidden nodes and resulted in an r² of 0.97. The prediction rate of profiles for this model was again 66%, and the 10 observations taken from the remediated transects were classified with four as reference (not impacted), two as moderate, and four as heavily trafficked. Although the ANN included more comprehensive data, it classified eight of the 10 remediated transects at the usage extremes (reference or heavy traffic). Inspection of the novelty indexes from the prediction outputs showed that the input vectors from the remediated transects were very different from the data used to train the ANN. This difference suggests as a soil is remediated it does not escalate through states of succession in the same way as it descends following disturbance. We propose to explore this hysteresis between disturbance and recovery process as a predictor of the resilience of the microbial community to repeated disturbance/recovery cycles.     

Biologic activity of antigen receptors artificially incorporated onto B lymphocytes

We describe a method for incorporating monoclonal antibody molecules onto viable murine lymphocytes and summarize the biologic activity of these artificial receptors on B cells. Mouse spleen cells incubated overnight with palmitate conjugates of a monoclonal anti-DNP IgA (protein 315) in the presence of deoxycholic acid incorporate about 50,000 antibody molecules per cell. When concentrations of deoxycholate and palmitoyl-protein 315 are carefully controlled, this labeling procedure does not affect the viability or the normal functions of the receptor-decorated cells. The incorporated antibody specifically binds DNP-antigens, although it appears to be unable to communicate directly with internal cellular components. Yet when these receptor-decorated, unprimed cells are challenged with any one of several DNP-antigens, up to 42,000 per 10(6) B cells differentiate into Ig-secreting cells. This response is about 23-fold greater than that induced in normal cell cultures and is of the same magnitude as that induced by the polyclonal B cell activator LPS. This, in addition to the observation that only about 3.6% of receptor-decorated B cells responding to DNP-conjugated polymerized flagellin (DNP-POL) produce hapten-specific antibody, demonstrates that these antigens cause polyclonal B cell differentiation. Normal spleen cells in the presence of DNP-POL and irradiated spleen cells bearing the artificial receptors do not exhibit the polyclonal antibody response. Also, the response of receptor-decorated B cell is blocked by high but nontoxic concentrations of the nonimmunogenic hapten DNP-lysine. These observations demonstrate that the polyclonal B cell response in this system requires the binding of antigen to artificial receptors on functionally viable cells. The polyclonal B cell response to a thymus-dependent antigen DNP-conjugated bovine gamma-globulin (DNP-BGG) requires the presence of the carrier-primed T cells. On the other hand, T cell depletion by anti-Thy-1.2 monoclonal antibody and complement causes only a slight reduction in the number of receptor-decorated B cells that respond to the relatively thymus-independent antigen DNP-POL. This type of phenomenon is also seen with natural antigen-specific B cells. Thus, polyclonal activation of receptor-decorated B cells exhibits the same gross helper cell requirements as antigenic activation of natural antigen-specific B cells. The results of this study are discussed in the context of the role of membrane-bound surface Ig in antigen-dependent B cell activation.(ABSTRACT TRUNCATED AT 400 WORDS)