Drought legacy interacts with wildfire to alter soil microbial communities in a Mediterranean climate-type forest

Mediterranean forest ecosystems will be increasingly affected by hotter drought and more frequent and severe wildfire events in the future. However, little is known about the longer-term responses of these forests to multiple disturbances and the forests' capacity to maintain ecosystem function. This is particularly so for below-ground organisms, which have received less attention than those above-ground, despite their essential contributions to forest function. We investigated rhizosphere microbial communities in a resprouting Eucalyptus marginata forest, southwestern Australia, that had experienced a severe wildfire four years previously, and a hotter drought eight years previously. Our aim was to understand how microbial communities are affected over longer-term trajectories by hotter drought and wildfire, singularly, and in combination. Fungal and bacterial DNA was extracted from soil samples, amplified, and subjected to high throughput sequencing. Richness, diversity, composition, and putative functional groups were then examined. We found a monotonic decrease in fungal, but not bacterial, richness and diversity with increasing disturbance with the greatest changes resulting from the combination of drought and wildfire. Overall fungal and bacterial community composition reflected a stronger effect of fire than drought, but the combination of both produced the greatest number of indicator taxa for fungi, and a significant negative effect on the abundance of several fungal functional groups. Key mycorrhizal fungi, fungal saprotrophs and fungal pathogens were found at lower proportions in sites affected by drought plus wildfire. Wildfire had a positive effect on bacterial hydrogen and bacterial nitrogen recyclers. Fungal community composition was positively correlated with live tree height. These results suggest that microbial communities, in particular key fungal functional groups, are highly responsive to wildfire following drought. Thus, a legacy of past climate conditions such as hotter drought can be important for mediating the responses of soil microbial communities to subsequent disturbance like wildfire.

How much organic carbon could the soil store? The carbon sequestration potential of Australian soil

Soil is a huge carbon (C) reservoir, but where and how much extra C can be stored is unknown. Current methods to estimate the maximum amount of mineral-associated organic carbon (MAOC) stabilized in the fine fraction (clay + silt,< 20 μm $$ <20\;\upmu \mathrm{m} $$ ) fit through the MAOC versus clay + silt relationship, not their maxima, making their estimates more uncertain and unreliable. We need a function that 'envelopes' that relationship. Here, using 5089 observations, we estimated that the uppermost 30 cm of Australian soil holds 13 Gt (10-18 Gt) of MAOC. We then fitted frontier lines, by soil type, to the relationship between MAOC and the percentage of clay + silt to estimate the maximum amounts of MAOC that Australian soils could store in their current environments, and calculated the MAOC deficit, or C sequestration potential. We propagated the uncertainties from the frontier line fitting and mapped the estimates of these values over Australia using machine learning and kriging with external drift. The maps show regions where the soil is more in MAOC deficit and has greater sequestration potential. The modelling shows that the variation over the whole continent is determined mainly by climate, linked to vegetation and soil mineralogy. We find that the MAOC deficit in Australian soil is 40 Gt (25-60 Gt). The deficit in the vast rangelands is 20.84 Gt (13.97-29.70 Gt) and the deficit in cropping soil is 1.63 Gt (1.12-2.32 Gt). Management could increase C sequestration in these regions if the climate allowed it. Our findings provide new information on the C sequestration potential of Australian soils and highlight priority regions for soil management. Australia could benefit environmentally, socially and economically by unlocking even a tiny portion of its soil's C sequestration potential.

In search of a counter you can count on: relative efficacy of human visual and automated colony counting

To evaluate comparative efficiency of traditional vs automated colony counting methods, cultures of Escherichia coli (ATCC 25945), Staphylococcus epidermidis (ATCC 12225), Streptococcus pyogenes (ATCC19615) and Streptococcus pneumoniae (ATCC49619) were prepared as pure cultures and mixed cultures at 0·5 McFarland standard and serial dilutions were performed. Plates were inoculated in triplicate with 50, 125, 250 and 500 colony forming units and counted by four researchers, visually and using each of the automated counters. Colony count and counting time were recorded. The pattern of efficiency for all bacterial species was similar: plates with low counts were accurate and quick to count for all methods, with an increase in time and a decrease in accuracy and precision as counts rose. Higher counts of single round colonies required less time and had greater precision with automated counters than human visual counting counts with no loss of accuracy; however, counts were reduced in accuracy and increased in time for species with less regular morphology or when plates had mixed species. Surprisingly, a free phone application was only slightly less precise and more time consuming than the high-end professional counter indicating that automation may be achievable at lower cost than expected.

SIGNIFICANCE AND IMPACT OF THE STUDY

Colony quantification is essential in clinical and research settings as well as pedagogy at the college level. Human visual (HV) counting, the most common method, is time consuming and fraught with errors. The time, accuracy and precision of HV counting were compared to a high-end professional automated counter, an inexpensive phone application and a free phone application. Low cost benefits of increased speed and accuracy with automated counting are maximized when counting single round colonies; but much reduced if colonies have irregular morphology or demonstrate haemolysis.

The effect of 2-methoxyoestrone-3-O-sulphamate on the growth of breast cancer cells and induced mammary tumours

2-Methoxyoestrogens are emerging as a new class of drug that can inhibit tumour growth and angiogenesis. As sulphamoylation of oestrogens enhances their potency and bioavailability we have synthesized 2-methoxyoestrone-3-O-sulphamate (2-MeOEMATE) and compared its ability to inhibit the proliferation of breast cancer cells with that of 2-methoxyoestrone (2-MeOE1). 2-MeOEMATE (1 microM) inhibited the growth of oestrogen receptor positive MCF-7 breast cancer cells by 52% whereas 2-MeOE1 had little effect at this concentration. 2-MeOEMATE also inhibited the growth of oestrogen receptor negative MDA-MB-231 breast cancer cells. Exposure of cells to 2-MeOEMATE caused them to round up and become detached suggesting that this compound may induce cells to undergo apoptosis. Cell cycle analysis revealed that 2-MeOEMATE caused cells to arrest in the G(2)/M phase with the increase in G(2)/M arrested cells being detectable by 12 hr. Exposure of MCF-7 cells to 2 L-MeOEMATE for 24 hr followed by culture in drug-free medium for 24 hr did not reverse the arrest of cells in the G(2)/M phase. TUNEL analysis confirmed that 2-MeOEMATE induced apoptosis in a significant proportion of treated MCF-7 cells. In an in vivo study, employing nitrosomethylurea-induced mammary tumours in intact rats, 2-MeOE1 (20mg/kg/d, p.o. for 11 days) had little effect on tumour growth. In contrast, the same dose of 2-MeOEMATE resulted in the almost complete regression of 2/3 tumours over an 11-day period. We conclude that 2-MeOEMATE should have considerable therapeutic potential for the treatment of breast tumours.

Stimulating cancer screening among Latinas and African-American women. A community case study

Recent studies have attributed underutilization of early cancer detection programs among the disadvantaged to knowledge deficits and myths, lack of belief in cancer susceptibility (denial), and such attitudinal barriers as fear and embarrassment. Video modalities have been demonstrated to be effective in increasing knowledge and promoting health-protective behavior in low-income people of color. Waiting rooms of public health clinic facilities in large urban areas provide a captive audience of predominantly African Americans and Latinos with a preference for obtaining health information from audiovisual media. The development of a culturally sensitive, cost-effective documentary format is described. An experience of rapid acceleration in demand for Pap smears in an underserved Latino community of East Los Angeles following the showing of one of these videos is chronicled as a spontaneous and informal evaluation of this approach to health education/promotion video production.