Viscophobic turning regulates microalgae transport in viscosity gradients

Gradients in fluid viscosity characterize microbiomes ranging from mucus layers on marine organisms1 and human viscera2,3 to biofilms4. While such environments are widely recognized for their protective effects against pathogens and their ability to influence cell motility2,5, the physical mechanisms controlling cell transport in viscosity gradients remain elusive6–8, primarily due to a lack of quantitative observations. Through microfluidic experiments with a model biflagellated microalga (Chlamydomonas reinhardtii), we show that cells accumulate in high viscosity regions of weak gradients as expected, stemming from their locally reduced swimming speed. However, this expectation is subverted in strong viscosity gradients, where a novel viscophobic turning motility – consistent with a flagellar thrust imbalance9,10 – reorients the swimmers down the gradient and causes striking accumulation in low viscosity zones. Corroborated by Langevin simulations and a three-point force model of cell propulsion, our results illustrate how the competition between viscophobic turning and viscous slowdown ultimately dictates the fate of population scale microbial transport in viscosity gradients.

Metagenomic investigation of African dust events in the Caribbean

ABSTRACT African dust from the Sahara and Sahel regions of Northern Africa is blown intercontinental distances and is the highest portion of atmospheric dust generated each year. During the Northern Hemisphere summer months (boreal summer), these dust events travel into the Caribbean and southern United States. While viability assays, microscopy and bacterial amplicon analyses have shown that dust-associated microbes may be diverse, the specific microbial taxa that are transported intercontinental distances with these dust events remain poorly characterized. To provide new insights into these issues, five metagenomes of Saharan dust events occurring in the Caribbean, collected in the summer months of 2002 and 2008, were analyzed. The data revealed that similar microbial composition existed between three out of the five of the distinct dust events and that fungi were a prominent feature of the metagenomes compared to other environmental samples. These results have implications for better understanding of microbial transport through the atmosphere and may implicate that the dust-associated microbial load transiting the Atlantic with Saharan dust is similar from year to year.

Narrow Grass Hedge Effects on Microbial Transport Following Variable Applications of Beef Cattle Manure

The effectiveness of a 1.4 m wide grass hedge in reducing microbial transport following manure application was examined in this study. Beef cattle manure was applied to 0.75 m wide by 4.0 m long plots established on an Aksarben silty clay loam located in southeast Nebraska. Manure was added at rates required to meet none or the 1-, 2-, or 4-year nitrogen requirements for corn. The transport of phages, total coliforms, , and enterococci was measured for three 30 min simulated rainfall events, which were separated by approximately 24 h intervals. The narrow grass hedge reduced total counts of phages, , and enterococci from 10.8 to 9.01 log PFU ha-1, from 12.4 to 11.9 log CFU ha-1, and from 11.8 to 11.2 log CFU ha-1, respectively. For the plots that received manure, no significant differences in transport of phages or enterococci were found among the three manure application rates. Rainfall simulation run significantly affected measurements of phages, total coliforms, and enterococci, with measurements during the three runs varying from 8.91 to 10.5 log PFU ha-1, from 12.7 to 13.3 log CFU ha-1, and from 11.2 to 11.7 log CFU ha-1, respectively. Counts for phages, total coliforms, and enterococci were significantly less for the first than the second and third rainfall simulation runs. All four of the microbial constituents were significantly correlated to dissolved P, particulate P, total P, and total N. A narrow grass hedge placed on the contour significantly reduced microbial transport following variable applications of beef cattle manure. Keywords: Bacteria, Cattle manure, E. coli, Filter strips, Land application, Manure management, Manure runoff, Microbial, Microorganisms, Runoff.

Wheat Strip Effects on Microbial Transport Following Variable Applications of Beef Cattle Manure

Vegetative filter strips (VFS) consisting of perennial vegetation have been successfully used to reduce the transport of contaminants in runoff from land application areas. The effectiveness of a winter wheat strip, which may be more acceptable to producers, in reducing microbial transport was examined in this study. A 1.4 m wheat strip was used to allow direct comparison with experimental results obtained in previous studies. Beef cattle manure was applied to 0.75 m wide by 4.0 m long plots established on an Aksarben silty clay loam located in southeast Nebraska. Manure was added at rates required to meet the 0- 1-, 2-, or 4-year phosphorus requirement for corn. The transport of selected microbes was measured for three 30 min simulated rainfall events separated by 24 h intervals. The narrow wheat strip did not significantly reduce counts of any of the measured microbes. The application of manure to meet the 4-year P requirement resulted in and enterococci loads that were significantly greater than the 1-year P requirement. Rainfall simulation run significantly affected measurements of phages, total coliforms, , and enterococci, with measurements during the three runs varying from 9.35 to 10.9 log plaque-forming units (PFU) ha-1, from 11.5 to 12.1 log colony-forming units (CFU) ha-1, from 12.1 to 12.5 log CFU ha-1, and from 11.1 to 11.4 log CFU ha-1, respectively. The transport of was found to be significantly correlated to selected nutrient loads and electrical conductivity of runoff. The presence of narrow wheat strips did not reduce microbial loads in runoff. Keywords: Bacteria, Cattle manure, E. coli, Filter strips, Land application, Manure management, Manure runoff, Microbial, Microorganisms, Runoff.