Ecological and social modeling for migration and adhesion pattern of a benthic diatom

Simulation of various biofilm fractal morphologies by agent-based model

Biofilms are clusters of bacteria wrapped in extracellular matrix and polymers. The study of biofilm morphological transformation has been around for a long time and has attracted widespread attention. In this paper, we present a model for biofilm growth based on the interaction force, in which bacteria are treated as tiny particles and locations of particles are updated by calculating the repulsive forces among particles. We adapt a continuity equation to indicate nutrient concentration variation in the substrate. Based on the above, we study the morphological transformation of biofilms. We find that nutrient concentration and nutrient diffusion rate dominate different biofilm morphological transition processes, in which biofilms would grow into fractal morphology under the conditions of low nutrient concentration and nutrient diffusivity. At the same time, we expand our model by introducing a second particle to mimic extracellular polymeric substances (EPS) in biofilms. We find that the interaction between different particles can lead to phase separation patterns between cells and EPSs, and the adhesion effect of EPS can attenuate this phenomenon. In contrast to single particle system models, branches are inhibited due to EPS filling in dual particle system models, and this invalidation is boosted by the enhancement of the depletion effect.

Underestimated methane production triggered by phytoplankton succession in river-reservoir systems: Evidence from a microcosm study

The impoundment of dammed rivers accelerates phytoplankton succession from river-dominated to lake-dominated species. Little is known about the role of phytoplankton succession in methane (CH₄) production. In this study, we performed a 61-day microcosm investigation to simulate the collapse processes of Cyclotella meneghiniana (river-dominated algae) and Chlorella pyrenoidosa and Microcystis aeruginosa (lake-dominated algae). The results suggested that different methanogenic conditions were induced by the collapse of river-and lake-dominated algae. The rapid settlement of C. meneghiniana induced aerobic conditions in the water that inhibited anaerobic CH₄ production and intensified CH₄ oxidation as a result of an increase in pmoA. However, the decomposition of C. pyrenoidosa and M. aeruginosa depleted dissolved oxygen and provided abundant labile organic matter, which jointly elevated mcrA and the mcrA/pmoA ratio. Under this condition, anaerobic CH₄ production was the dominant pathway for the mineralization of algae-derived carbon. Finally, the CH₄ produced per unit of particulate total carbon (identified as the carbon content of the algal biomass) by C. pyrenoidosa and M. aeruginosa was 16.29-fold and 8.56-fold higher, respectively, than that produced by C. meneghiniana. These observations provided evidence that lake-dominated algae played a more vital role in CH₄ production than river-dominated algae when algal succession occurred. This discovery might be a new and vital, yet largely underestimated CH₄ emission pathway in river-reservoir systems, that should be considered when evaluating the effect of hydraulic projects on greenhouse gas emissions.

The Alterations of Biofilm Formation and EPS Characteristics of a Diatom by a Sponge-Associated Bacterium Psychrobacter sp

A sponge-associated bacterium, which was identified as Psychrobacter sp. in this study, was found with high activity against biofilm formation of benthic diatoms, including Amphora sp., Nitzschia closterium, Nitzschia frustulum, and Stauroneis sp. The activity against diatom biofilm formation by the tested strain was confirmed mostly in the culture supernatant and could be extracted using organic solvents. Treatment with its supernatant crude extract significantly reduced the cells of Stauroneis sp. forming biofilm and slightly increased the cells floating in the culture medium, which results in the ratio of biofilm cell/floating cell altering from 0.736 in control to 0.414 in treatment. Use of the supernatant crude extract led to increased production of extracellular polymeric substances (EPSs) by diatom Stauroneis sp. from 16.66 to 41.59 (g/g cell dry weight). The increase in EPS production was mainly contributed by soluble EPS (SL-EPS) and followed by the EPS that was tightly bound to biofilm cells (BF-TB-EPS). In addition, the supernatant crude extract caused significant changes in the monosaccharides composition of the EPS of Stauroneis sp. Specifically, glucuronic acid (Glc-A) and N-acetyl-D-glucosamine (Glc-NAc) in BF-TB-EPS were 55% fold decreased and 1219% fold increased, respectively. Based on our findings, we proposed that these changes in monosaccharides composition might lead to a decreased biofilm formation efficiency of diatom.