Bacterial chemotaxis to effluent from a rum distillery in tropical near-shore coastal waters

Hydrodynamic effects on microcapillary motility and chemotaxis assays of Methylosinus trichosporium OB3b

A study of the random motility and chemotaxis of Methylosinus trichosporium OB3b was conducted by using Palleroni-chamber microcapillary assay procedures. Under the growth conditions employed, this methanotroph was observed qualitatively with a microscope to be either slightly motile or essentially nonmotile. However, the cells did not not respond in the microcapillary assays in the manner expected for nonmotile Brownian particles. As a consequence, several hydrodynamic effects on these Palleroni microcapillary assays were uncovered. In the random-motility microcapillary assay, nondiffusive cell accumulations occurred that were strongly dependent upon cell concentration. An apparent minimal random-motility coefficient (mu) for this bacterial cell of 1.0 x 10(-7) cm2/s was estimated from microcapillary assays. A simple alternative spectrophotometric assay, based upon gravitational settling, was developed and shown to be an improvement over the Palleroni microcapillary motility assay for M. trichosporium OB3b in that it yielded a more-accurate threefold-lower random-motility coefficient. In addition, it provided a calculation of the gravitational-settling velocity. In the chemotaxis microcapillary assay, the apparent chemotactic responses were strongest for the highest test-chemical concentrations in the microcapillaries, were correlated with microcapillary fluid density, and were strongly dependent upon the microcapillary volume. A simple method to establish the maximal concentration of a chemical that can be tested and to quantify any contributions of abiotic convection is described. Investigators should be aware of the potential problems due to density-driven convection when using these commonly employed microcapillary assays for studying cells which have low motilities.

In situ survival of Vibrio cholerae and Escherichia coli in tropical coral reefs

Vibrio cholerae and Escherichia coli were inoculated into membrane diffusion chambers and placed around two small coral reef islands in Puerto Rico and monitored for 5 days. Several chambers were also buried in the sands of one of the reefs. Both E. coli and V. cholerae densities declined by 2 orders of magnitude, as measured by direct particle counts with a Coulter Counter (Coulter Electronics, Inc., Hialeah, Fla.). However, the density of neither bacteria changed dramatically when the same samples were analyzed by epifluorescent direct counts. Differences in the two direct count methods were accounted for by changes in cell morphology that occurred in both bacteria after exposure to seawater. Morphological changes occurred more rapidly in E. coli compared with those in V. cholerae. Bacteria in chambers exposed to sediment did not show significant changes in morphology and had only a slight decline in density. Physiological activity declined by more than 40% for both bacteria within 24 h. The decline in activity was less severe in the sediments. Tropical coral reef sands and turtle grass beds were shown to be less stressful environments for V. cholerae and E. coli than would have been predicted from temperature and microcosm studies. V. cholerae can survive the in situ conditions of a tropical coral reef and could become a source of bacterial contamination for fish and shellfish in this environment. The simultaneous monitoring of E. coli levels established that this bacteria can not be used as an indicator of V. cholerae or other fecal-borne pathogens in coral reef environments because of the greater stress these environments put on E. coli. Both bacteria could be of greater public health importance in tropical marine areas than previously imagined.

Comparison of the in situ survival and activity ofKlebsiella pneumoniae andEscherichia coli in tropical marine environments

A near-shore coastal mangrove island receiving untreated sewage and a coastal cove receiving rum distillery effluent in Puerto Rico were examined for their ability to support survival and activity ofKlebsiella pneumoniae andEscherichia coli. Pure cultures of both bacteria were monitored for 96 hours in situ at both locations using membrane diffusion chambers.K. pneumoniae survived at all sites as measured by AODC and Coulter Counter direct counts. However, at the mangrove island less than 20% of theK. pneumoniae population was active (AODC) after the first 3 hours and less than 10% of this population was respiring (INT). In contrast, the coastal area which was receiving rum distillery effluent was able to maintain 40% of theK. pneumoniae population in an active state with 90% respiring. TheE. coli population declined by two orders of magnitude at the mangrove island, but remained unchanged at the rum distillery outfall. TheE. coli population had a higher proportion of active cells and respiring cells thanK. pneumoniae at all sites. At the rum distillery site, theE. coli population was remarkable in that 95% remained active and 99% were respiring. This study suggests that, when sufficient organic loading exists,E. coli, a "nonsurvivor," can overcome the bactericidal effects of tropical marine waters.K. pneumoniae, a "survivor," could survive under all conditions but could not maintain the activity or respiration that theE. coli population could, even when high organic loads were present. Morphological changes related to nutrient stress in the tropical marine environment were apparent inE. coli, but not inK. pneumoniae. Based on physiological activityE. coli is just as much a "survivor" asK. pneumoniae in tropical marine waters.

Comparison of four membrane filter methods for fecal coliform enumeration in tropical waters

Four membrane filter methods for the enumeration of fecal coliforms were compared for accuracy, specificity, and recovery. Water samples were taken several times from 13 marine, 1 estuarine, and 4 freshwater sites around Puerto Rico, from pristine waters and waters receiving treated and untreated sewage and effluent from a tuna cannery and a rum distillery. Differences of 1 to 3 orders of magnitude in the levels of fecal coliforms were observed in some samples by different recovery techniques. Marine water samples gave poorer results, in terms of specificity, selectivity, and comparability, than freshwater samples for all four fecal coliform methods used. The method using Difco m-FC agar with a resuscitation step gave the best overall results; however, even this method gave higher false-positive error, higher undetected-target error, lower selectivity, and higher recovery of nontarget organisms than the method using MacConkey membrane broth, the worst method for temperate waters. All methods tested were unacceptable for the enumeration of fecal coliforms in tropical fresh and marine waters. Thus, considering the high densities of fecal coliforms observed at most sites in Puerto Rico by all these methods, it would seem that these density estimates are, in many cases, grossly overestimating the degree of recent fecal contamination. Since Escherichia coli appears to be a normal inhabitant of tropical waters, fecal contamination may be indicated when none is present. Using fecal coliforms as an indicator is grossly inadequate for the detection of recent human fecal contamination and associated pathogens in both marine and fresh tropical waters.