FIG. 3.
Limited exposure to TAN 31504 is sufficient to produce an increase in host mortality rate. (A to D) Bright-field micrographs of the vulva-uterus regions of Glp adult worms; the vulva is placed toward the bottom and the intestine is positioned toward the top of each worm body image, with the uterus situated directly above the vulva and below the intestine (×200 magnification). The black arrowheads point to the vulvas. (A to C) Accumulation of the food source bacteria within the nematode uterus was not found after 4 days of continuous exposure to the standard-food-source condition (A) or to L. chromiireducens subsp. chromiireducens LMG 22506 (B); however, uterine accumulation of L. chromiireducens subsp. solipictus TAN 31504 was observed (C). (D) Extensive uterine infection in a worm initially exposed to TAN 31504 for 24 h followed by 3 days of exposure to the standard food source. Similar extensive uterine infections were observed in worms exposed to mixed lawns of TAN 31504 and OP50-1 comprised of only 3 to 6% TAN 31504. (E) Survival curves of Glp adult N2 worms exposed continuously and discretely to pathogen. OP50-1, TAN 31504, and LMG 22506 indicate constant exposure to the respective pathogens. “24hLMG 22506” indicates an initial 24-h exposure to LMG 22506 followed by an extended exposure to TAN 31504. “12hTAN 31504” and “24hTAN 31504” indicate initial 12-h and 24-h exposures to TAN 31504, respectively, followed by extended exposure to standard-food-source lawns. Survival curves begin with time zero set to the time just prior to application of the infection conditions described above. The remaining worm populations on OP50-1 and LMG 22506 were censored after 10 days. Initial exposure to LMG 22506 did not appear to offer extended protection with regard to host life span extension over the TAN 31504 condition. Although from time zero the average 19.1-h extension in mean life span observed was significant (log rank P = 0.044), it was less than the 24-h period of initial LMG 22506 exposure (LTmean = 130.8 ± 3.9 h for 24 h of LMG 22506 exposure and 111.7 ± 6.5 h for TAN 31504). The brief 12-h exposure to TAN 31504 was sufficient to increase the host mortality rate (LTmean = 90.9 ± 4.2 h) significantly over that yielded by the constant exposure condition (log rank, P = 0.0041). The shortened host life span produced by the 24-h TAN 31504 condition (LTmean = 96.8 ± 7.9 h) was no different from that generated by the 12-h TAN 31504 condition (log rank, P = 0.66), nor was it significantly resolvable from that produced by the constant exposure condition (log rank, P = 0.26). (F) Survival curves of Glp adult N2 worms exposed to LB lawns consisting of varied ratios of bacteria. “100%” indicates exposure to pure lawns of TAN 31504; “0%” indicates exposure to pure lawns of OP50-1; and “3%,” “6%,” “31%,” and “67%” represent proportions of TAN 31504 to OP50-1 at the time of worm exposure. Host mortality rate was significantly enhanced by exposure to TAN 31504 (100%) compared to OP50-1 (0%) (log rank, P = 0.010; LTmean = 151.4 ± 7.7 h and 183.4 ± 5.8, respectively). Worms exposed to the 3%, 6%, and 37% lawns displayed an enhanced mortality rate compared to those exposed to the pure TAN 31504 lawn (log rank, P < 0.0001, P < 0.0001, and P = 0.0024, respectively; LTmean = 103.8 ± 3.4 h, 114.7 ± 4.0 h, and 125.7 ± 5.0 h, respectively). The mean host life span (LTmean = 132.4 ± 5.9 h) on the 67% lawn was shorter than that exhibited on the OP50-1 lawn (log rank, P < 0.0001), but was not significantly different from that displayed on the 100% lawn (log rank, P = 0.081).