Altering Microbiomes with Hydroxyapatite Nanoparticles: A Metagenomic Analysis

Abstract

Hydroxyapatite (HAp), the most abundant biological material among mammals, has been recently demonstrated to possess moderate antibacterial properties. Metagenomics provides a series of tools for analyzing the simultaneous interaction of materials with larger communities of microbes, which may aid in optimizing the antibacterial activity of a material such as HAp. Here, a microbiome intrinsic to the sample of sandy soil collected from the base of an African Natal plum (Carissa macrocarpa) shrub surrounding the children’s sandbox at the Arrowhead Park in Irvine, California was challenged with HAp nanoparticles and analyzed with next-generation sequencing for hypervariable 16S ribosomal DNA base pair homologies. HAp nanoparticles overwhelmingly reduced the presence of Gram-negative phyla, classes, orders, families, genera and species, and consequently elevated the relative presence of their Gram-positive counterparts. Thermodynamic, electrostatic and chemical bonding arguments were combined in a model proposed to explain this selective affinity. The ability of amphiphilic surface protrusions of lipoteichoic acid in Gram-positive bacteria and mycolic acid in mycobacteria to increase the dispersibility of the bacterial cells and assist in their resistance to capture by the solid phase is highlighted. Within the Gram-negative group, the variability of the distal, O-antigen portion of the membrane lipopolysaccharide was shown to be excessive and the variability of its proximal, lipid A portion insufficient to explain the selectivity based on chemical sequence arguments. Instead, flagella-driven motility proves to be a factor favoring the evasion of binding to HAp. HAp displayed a preference toward binding to less pathogenic bacteria than those causative of disease in humans, while taxa having a positive agricultural effect were largely captured by HAp, indicating an evolutionary advantage this may have given it as a biological material. The capacity to selectively sequester Gram-negative microorganisms and correspondingly alter the composition of the microbiome may open up a new avenue in environmental and biomedical applications of HAp.

Teaching Chess History to Students in Natural Sciences: How to Do It and Why

“…The same goes for homemade research, carried out in more intimate settings than those of the mainstream labs of academic institutions and industrial sites: they connect to the young people, according to my experience, much better than the formally conducted research, alongside transmitting the noble idea that everyone at any time can be a creator and conductor of experiments that can change the world. At this spot, an excursion is made to the aforementioned research from my personal oeuvre in the early 2020s, when the excommunication from academia for political reasons, the loss of employment and the closure of an institutional lab inspired me to involve myself and children in research carried out in home bedrooms 75 , garages 76 , kitchens 77,78 , backyards 79 , lakes 80 , parks 81 , pools 82 and playgrounds 83,84 , arriving at far more stimulating findings and presenting them in far more inspirational ways than ever before. At the time this game was played, in May 1991, a bigger conflict was looming over my world than that taking place on the chessboard before me.…”