An in vitro tumorigenesis model based on live-cell-generated oxygen and nutrient gradients

The tumor microenvironment (TME) is multi-cellular, spatially heterogenous, and contains cell-generated gradients of soluble molecules. Current cell-based model systems lack this complexity or are difficult to interrogate microscopically. We present a 2D live-cell chamber that approximates the TME and demonstrate that breast cancer cells and macrophages generate hypoxic and nutrient gradients, self-organize, and have spatially varying phenotypes along the gradients, leading to new insights into tumorigenesis.

An in vitro tumorigenesis model based on live cell-generated oxygen and nutrient gradients

The tumor microenvironment (TME) is multi-cellular, spatially heterogenous, and contains cell-generated gradients of soluble molecules. Current cell-based model systems lack this complexity or are difficult to interrogate microscopically. We present a 2D live-cell chamber that approximates the TME and demonstrate that breast cancer cells and macrophages generate hypoxic and nutrient gradients, self-organize, and have spatially varying phenotypes along the gradients, leading to new insights into tumorigenesis.

Preferential flow induced nutrient gradients create microbial hotspots and shape bacterial community structure

<p>In this study we used oxygen sensitive optodes, or optical sensor devices, to observe oxygen depletion by soil microbes. Depletion served as a reference for microbial activity along three artificially constructed preferential flow paths consisting of coarse sand in the center surrounded fine sand. Following a flow event with glucose addition, images showed that oxygen depletion is greatest along the boundary between preferential flow paths (coarse sand) and the bulk matrix (fine sand). Oxygen gradients as well as nutrient gradients are commonly attributed to shaping soil bacterial communities, however, these mechanisms have not been studied in the specific soil architecture of preferential flow paths. A separate experiment was performed in which the fine sand matrix was replaced with a sandy soil containing its native microbial community. An addition of glucose and DOM was flowed through the columns containing real soil. Oxygen depletion was again monitored using oxygen sensor foils. To assess changes in the microbial community in time 16S rRNA analysis was performed on soil samples taken from different locations within the chambers. By monitoring the levels of oxygen depletion in time, we are able to gain an understanding of how this dynamic process alters microbial community structure. Additionally, zymography was performed to elucidate the locations where enzyme activity was greatest. By studying the microbial community in time along with oxygen depletion and enzyme activity, we are able to gain insight into structure-function relationships that take place within preferential flow paths. Furthering our understanding of processes taking place within preferential flow paths will allow for better estimation of how these entities function biogeochemically.</p>

Growth-rate dependent resource investment in bacterial motile behavior quantitatively follows potential benefit of chemotaxis

Microorganisms possess diverse mechanisms to regulate investment into individual cellular processes according to their environment. How these regulatory strategies reflect the inherent trade-off between the benefit and cost of resource investment remains largely unknown, particularly for many cellular functions that are not immediately related to growth. Here, we investigate regulation of motility and chemotaxis, one of the most complex and costly bacterial behaviors, as a function of bacterial growth rate. We show with experiment and theory that in poor nutritional conditions,Escherichia coliincreases its investment in motility in proportion to the reproductive fitness advantage provided by the ability to follow nutrient gradients. Since this growth-rate dependent regulation of motility genes occurs even when nutrient gradients are absent, we hypothesize that it reflects an anticipatory preallocation of cellular resources. Notably, relative fitness benefit of chemotaxis could be observed not only in the presence of imposed gradients of secondary nutrients but also in initially homogeneous bacterial cultures, suggesting that bacteria can generate local gradients of carbon sources and excreted metabolites, and subsequently use chemotaxis to enhance the utilization of these compounds. This interplay between metabolite excretion and their chemotaxis-dependent reutilization is likely to play an important general role in microbial communities.