Optimal thermotolerance of Bifidobacterium bifidum in gellan-alginate microparticles

The purpose of this research was to encapsulate Bifidobacterium bifidum using gellan, sodium alginate and prebiotics as coating materials, and to maximize the thermotolerance of the probiotics with an optimal combination of the coating materials. The optimal ratio of the coating materials for the microparticles under heat treatments (75 degrees C, 1 min) was obtained by using the response surface method and the sequential quadratic programming technique. Optimization results indicated that 2% sodium alginate mixed with 1% gellan gum as coating materials would produce the highest thermotolerance in terms of B. bifidum count. The verification experiment yielded a result close to the predicted values, with no significant difference (P > 0.05). The results of heat treatments also demonstrated that the addition of gellan gum in the walls of probiotic microcapsules provided improved protection for B. bifidum. These probiotic counts remained at 10(5)-10(6) CFU/g for the microcapsules stored for 2 months, then treated in heat and in simulated gastric fluid.     

Transient persistence of bobcat (Lynx rufus) occurrence throughout a human-dominated landscape

Human developments have detrimental effects on wildlife populations globally with carnivores being particularly sensitive. The bobcat (Lynx rufus) is often considered an adaptable mesocarnivore that occurs throughout varied landcover types within its wide distribution and may be less susceptible to the negative effects of development. Our objectives were to investigate the landscape occupancy dynamics of bobcats in a highly developed and densely populated region of the northeastern United States to evaluate the sensitivity of bobcat occurrence to natural and anthropogenic landscape features. We established a large-scale camera trapping survey throughout Rhode Island, USA, sampling from 2018 to 2020. Using dynamic occupancy models, we found initial site occupancy was positively influenced by the amount of forested wetland habitat, while increasing road density and shrub cover negatively influenced the probability of site colonization. Surprisingly, we found no hypothesized variables to influence site-level extirpation probability, or any seasonal effects on dynamic parameters. Lastly, we found that forest cover and road density negatively influenced the probability of detection. The probability of occupancy was high, >0.8, throughout much of the study area (49%), but we also found relatively high site transients, with the probability a site would change occurrence status from season to season at ≈0.27 in the majority of the study area (70%). Our results show that although bobcats can persist in human-dominated landscapes, they require contiguous natural areas to do so. Future expansion of road infrastructure may reduce habitat connectivity and increase road mortalities, thus jeopardizing the population.     

Response of Amazonian forests to mid-Holocene drought: A model-data comparison

There is a major concern for the fate of Amazonia over the coming century in the face of anthropogenic climate change. A key area of uncertainty is the scale of rainforest dieback to be expected under a future, drier climate. In this study, we use the middle Holocene (ca. 6000 years before present) as an approximate analogue for a drier future, given that palaeoclimate data show much of Amazonia was significantly drier than present at this time. Here, we use an ensemble of climate and vegetation models to explore the sensitivity of Amazonian biomes to mid-Holocene climate change. For this, we employ three dynamic vegetation models (JULES, IBIS, and SDGVM) forced by the bias-corrected mid-Holocene climate simulations from seven models that participated in the Palaeoclimate Modelling Intercomparison Project 3 (PMIP3). These model outputs are compared with a multi-proxy palaeoecological dataset to gain a better understanding of where in Amazonia we have most confidence in the mid-Holocene vegetation simulations. A robust feature of all simulations and palaeodata is that the central Amazonian rainforest biome is unaffected by mid-Holocene drought. Greater divergence in mid-Holocene simulations exists in ecotonal eastern and southern Amazonia. Vegetation models driven with climate models that simulate a drier mid-Holocene (100–150 mm per year decrease) better capture the observed (palaeodata) tropical forest dieback in these areas. Based on the relationship between simulated rainfall decrease and vegetation change, we find indications that in southern Amazonia the rate of tropical forest dieback was ~125,000 km² per 100 mm rainfall decrease in the mid-Holocene. This provides a baseline sensitivity of tropical forests to drought for this region (without human-driven changes to greenhouse gases, fire, and deforestation). We highlight the need for more palaeoecological and palaeoclimate data across lowland Amazonia to constrain model responses.     

生物结皮胞外多糖理化特性及菌群结构的季节动态

胞外多糖(EPS)是蓝藻重要抗逆物质,也是生物结皮中主要的碳储存形式,对结皮的物质循环、稳定度等具有重要作用。本研究以古尔班通古特沙漠不同季节(1月、4月、7月、10月)生物结皮为对象,对其EPS含量、组成、形貌特征及微生物群落结构进行了动态研究。结果表明: 1)EPS的分泌格局呈现明显的季节动态变化特征。1、4、7、10月EPS含量分别为81.72、52.46、76.77、70.54 μg·cm^-2,叶绿素a含量分别为2.7、4.94、4.2、5.98 μg·cm^-2,说明冬、夏两季蓝藻将固定的有机碳更多地分配给EPS,而春、秋两季则更多地用于自身生物量的积累。2)各个季节的EPS均由7种单糖组成,且葡萄糖和半乳糖的相对摩尔百分比之和为46%～56%,显著高于另外5种单糖;EPS的单糖组分与气温和降水之间具有显著的相关性;各季节EPS的傅里叶红外图谱无明显差别。3)原子力显微镜观测结果显示,7月、10月EPS具有更多的丝状及粗绳状结构,而1月、4月则呈块状结构。4)16S rDNA高通量测序结果表明,4个季节下蓝藻门和微鞘藻属始终为生物结皮优势细菌门和属,其相对丰度显著高于其他细菌门和属。变形菌门的相对丰度与岩藻糖和半乳糖的相对摩尔百分比呈显著正相关关系,说明单糖的百分比组成对结皮中异养细菌影响显著。在荒漠生境中,温度、水分等环境因子随季节变化显著,结皮胞外多糖理化特性及细菌群落的季节性变化受温度、水分、光照等气象因子的共同调控。     

拟南芥微丝加帽蛋白β亚基参与壳梭孢素诱导的气孔开放过程

气孔是植物响应外源信号,与环境进行水分和气体交换的门户。由外源信号引起的保卫细胞微丝骨架动态变化在气孔运动中发挥重要作用,但是具体的精确调节机制仍不清楚。微丝结合蛋白家族(ABPs) 是微丝动态组装最直接的调控者,它们的作用不容忽视。本文运用反向遗传学,以微丝结合蛋白—加帽蛋白 (CP) β-亚基 (CPB) 突变体cpb-3为实验材料,探究其在壳梭孢素 (FC)诱导气孔开放中的作用。结果发现:离体叶片干燥3 h,cpb-3突变体的叶片失水率为63.45%,明显高于野生型的48.99%。气孔开度测量及激光共聚焦显微镜观察发现,cpb-3突变体的气孔开放程度以及微丝动态重排对FC分子更敏感。气孔开度相比野生型增大了20% (P<0.05),含辐射状微丝排布的保卫细胞数量比例增幅达到58.3%,比对照组高出18.5%。此外,非损伤微测技术记录保卫细胞Ca²⁺、K⁺等跨膜运输动态,FC处理下,cpb-3突变体保卫细胞中Ca²⁺外流速度升至212.86 pmol cm^-2s^-1,野生型仅为68.76 pmol cm^-2s^-1,明显快于野生型。且K⁺内流也有相同表现。综上表明,微丝加帽蛋白CP的β亚基CPB可能通过调节保卫细胞微丝骨架动态重排以及离子流动,在FC诱导的气孔运动中发挥重要的作用。     

Dynamic investigation and modeling of the nitrogen cometabolism in Methylococcus capsulatus ( Bath)

The methanotrophic bacterium Methylococcus capsulatus is capable of assimilating methane and oxygen into protein-rich biomass, however, the diverse metabolism of the microorganism also allows for several undesired cometabolic side-reactions to occur. In this study, the ammonia cometabolism in Methylococcus capsulatus is investigated using pulse experiments. Surprisingly Methylococcus capsulatus oxidizes ammonia to nitrate through a yet unknown mechanism and fixes molecular nitrogen even at a high dissolved oxygen tension. The observed phenomena can be modeled using 14 ordinary differential equations and 18 kinetic parameters, of which 6 were revealed by Morris screening to be identifiable from the experimental data. Monte Carlo simulations showed that the model was robust and accurate even with uncertainty in the parameter values as confirmed by statistical error analysis.     

In silico strategies to couple production of bioethanol with growth in cyanobacteria

Cyanobacteria have been considered as promising candidates for sustainable bioproduction from inexpensive raw materials, as they grow on light, carbon dioxide, and minimal inorganic nutrients. In this study, we present a genome-scale metabolic network model for Synechocystis sp. PCC 6803 and study the optimal design of the strain for ethanol production by using a mixed integer linear problem reformulation of a bilevel programming problem that identifies gene knockouts which lead to coupling between growth and product synthesis. Five mutants were found, where the in silico model predicts coupling between biomass growth and ethanol production in photoautotrophic conditions. The best mutant gives an in silico ethanol production of 1.054 mmol·gDW ⁻¹·h ⁻¹.     

Sequence-specific dynamic information in proteins

We examine the local and global properties of the average B-factor, 〈B〉, as a residue-specific indicator of protein dynamic characteristics. It has been shown that values of 〈B〉 for the 20 amino acids differ in a statistically significant manner, and that, while strongly determined by the static physical properties of amino acids, they also encode averaged information about the influence of global fold on single-residue dynamics. Therefore, complete sequences of amino acids also encode fold-related global dynamic information, in addition to the local information that arises from static physical properties. We show that the relative magnitudes of these two contributions can be determined using Fourier methods, which represent the global properties of the sequences. It has also been shown that the behavior of Fourier components of 〈B〉 differs, with very high statistical significance, between structural groups, and that this information is not available from a comparable analysis of static amino acid properties.