Anna S. Persson

Transmission of BSA during cross-flow microfiltration: influence of pH and salt concentration

In many downstream processes microfiltration (MF) is used as the first step to separate the micro-organisms from the product-containing broth. The transmission of proteins through these MF membranes is of great importance, especially when a protein is the desired product. Usually, the largest fraction of the proteins retained in the membrane during the separation of micro-organisms is retained in the filter cake of micro-organisms that is built up on the membrane surface. However, this is not always the case. In some cases the transmission of proteins can decrease below 100% even though there are no micro-organisms present in the broth. In the present study the transmission of BSA through two different MF membranes (a nylon membrane, Pall Filtron Ultipore, Nylon66, 0.2 m, and a membrane made of polyether sulphone, Pall Filtron, Omega, 0.16 m) was investigated. The transmission of BSA was highest for the membrane that was said to be a low protein binding membrane (Omega) and it was affected by the pH in the solution. At pH 5, which is close to the IEP of the protein, the transmission was 100%, while at pH 3 and 7 the transmission was much lower (sometimes as low as 40%). However, when the ionic strength in the solution was increased the transmission of BSA through both MF membranes increased dramatically (at pH 3 and 7). This shows that the electrostatic interactions between the protein and the filter cake (made up of protein aggregates) and between the protein and the membrane affect the transmission. The increase in transmission when the protein is close to its IEP (at pH 5), is believed to be due to the lack of electrostatic repulsion between the proteins in the solution and filter cake of protein aggregates formed on the membrane. At high ionic strength the charged protein molecules are shielded from each other and from the membrane and the filter cake, by the ions in the solution. Due to this shielding effect the protein molecules act as if they were uncharged and the transmission of BSA is thus increased. (Less)

Separation of lactic acid-producing bacteria from fermentation broth using a ceramic microfiltration membrane with constant permeate flow

The influence of several operating parameters on the critical flux in the separation of lactic acid-producing bacteria from fermentation broth was studied using a ceramic microfiltration membrane equipped with a permeate pump. The operating parameters studied were crossflow velocity over the membrane, bacterial cell concentration, protein concentration, and pH. The influence of the isoelectric point (IEP) of the membrane was also investigated. In the interval studied (5.3-10.8 m/s), the crossflow velocity had a marked effect on the critical flux. When the crossflow velocity was increased the critical flux also increased. The bacterial cells were retained by the membrane and the concentration of bacterial cells did not affect the critical flux in the interval studied (1.1-3.1 g/L). The critical flux decreased when the protein concentration was increased. It was found that the protein was adsorbed on the membrane surface and protein retention occurred even though the conditions were such that no filter cake was present on the membrane surface. When the pH of the medium was lowered from 6 to 5 (and then further to 4) the critical flux decreased from 76 L/m(2)h to zero at both pH 5 and pH 4. This was found to be due to the fact that the lowering in pH had affected the physiology of the bacterial cells so that the bacteria tended to adhere to the membrane and to each other. The critical flux, for wheat flour hydrolysate without particles, was much lower (28 L/m(2)h) when using a membrane with an IEP of 5.5 than the critical flux of a membrane with an IEP at pH 7 (96 L/m(2)h). This was found to be due to an increased affinity of the bacteria for the membrane with the lower IEP.

Sparing Land for Biodiversity at Multiple Spatial Scales

A common approach to the conservation of farmland biodiversity and the promotion of multifunctional landscapes, particularly in landscapes containing only small remnants of non-crop habitats, has been to maintain landscape heterogeneity and reduce land-use intensity. In contrast, it has recently been shown that devoting specific areas of non-crop habitats to conservation, segregated from high-yielding farmland (‘land sparing’), can more effectively conserve biodiversity than promoting low-yielding, less intensively managed farmland occupying larger areas (‘land sharing’). In the present paper we suggest that the debate over the relative merits of land sparing or land sharing is partly blurred by the differing spatial scales at which it is suggested that land sparing should be applied. We argue that there is no single correct spatial scale for segregating biodiversity protection and commodity production in multifunctional landscapes. Instead we propose an alternative conceptual construct, which we call ‘multiple-scale land sparing’, targeting biodiversity and ecosystem services in transformed landscapes. We discuss how multiple-scale land sparing may overcome the apparent dichotomy between land sharing and land sparing and help to find acceptable compromises that conserve biodiversity and landscape multifunctionality.

Conversion of sodium lactate to lactic acid with water-splitting electrodialysis

The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.

Bumble bees show trait-dependent vulnerability to landscape simplification

Agricultural intensification has resulted in large-scale loss of bee pollinators, but while some species have been negatively affected others seem to endure changed conditions. It has been suggested that certain morphological, ecological and life-history traits make some species more vulnerable to landscape changes. Information on which traits make species vulnerable and why may aid conservation of declining species. We performed a comprehensive analysis of how multiple traits related to diet breadth, movement and nesting habits moderate vulnerability of bumble bees to landscape simplification. We surveyed bumble bees in flower-rich non-crop habitats in either complex landscapes (with small crop fields bordered by non-crop habitats), or simple landscapes (with larger fields and therefore less non-crop habitats). We analysed if landscape type interacted with colony size, queen emergence date, colony life-cycle length, nesting habitat, thorax width, proboscis length or variability in thorax and proboscis, to explain bumble bee abundances. Workers and males of species with above-ground nests, small sized colonies and long colony cycle were relatively less abundant in simple compared to in complex landscapes. Simple landscapes hosted fewer males of late emerging species and species with highly variable proboscis length. This suggests that both nesting habitat and spatio-temporal availability of food resources act as ecological filters for bumble bees. Colony size correlated with nesting habitat and queen emergence when correcting for phylogenetic correlations, suggesting that landscape simplification acts through effects on combinations of traits. Our results have consequences for conservation by suggesting that declining bumble bee species can be supported by providing adequate nesting habitats and preferred plant species throughout the season and within short distance from nesting habitats, to allow utilisation also by species having colonies with few workers.

Use of microfiltration as first step in recovery of protein A from fermentation broth

The flux and transmission of protein A during microfiltration have been studied. We studied the performance of two commercial membranes: one made of nylon (Pall Ultipore Nylon66, 0.2 µm) and one of polyether sulfone (Pall Omega, 0.16 µm). The Nylon66 membrane had by far the best transmission of protein A although a previous study showed that bovine serum albumin (BSA), often used to characterize membranes, had much better transmission through the Omega membrane. The membrane manufacturer also states that the Omega membrane is the best membrane for this kind of application because it is a low-protein-binding membrane. The lower transmission of the Omega membrane for protein A was assumed to be owing to its smaller pores and higher charge density in combination with the larger Stokes radius for protein A. When the pH was lowered, the Nylon66 membrane still had the higher transmission. It can thus be concluded that a membrane that is found suitable for the recovery process of one protein is not always the best choice for the recovery process for other proteins even though the membrane is low protein binding.

When beggars are choosers—How nesting of a solitary bee is affected by temporal dynamics of pollen plants in the landscape

Abstract Wild bees are declining in intensively farmed regions worldwide, threatening pollination services to flowering crops and wild plants. To halt bee declines, it is essential that conservation actions are based on a mechanistic understanding of how bee species utilize landscapes. We aimed at teasing apart how foraging resources in the landscape through the nesting season affected nesting and reproduction of a solitary bee in a farmland region. We investigated how availability of floral resources and potentially resource‐rich habitats surrounding nests affected nest provisioning and reproduction in the solitary polylectic bee Osmia bicornis. The study was performed in 18 landscape sectors dominated by agriculture, but varying in agricultural intensity in terms of proportion of organic crop fields and seminatural permanent pastures. Pasture‐rich sectors contained more oak (Quercus robur), which pollen analysis showed to be favored forage in early season. More oaks ≤100 m from nests led to higher proportions of oak pollen in nest provisions and increased speed of nest construction in early season, but this effect tapered off as flowering decreased. Late‐season pollen foraging was dominated by buttercup (Ranunculus spp.), common in various noncrop habitats. Foraging trips were longer with more oaks and increased further through the season. The opposite was found for buttercup. Oak and buttercup interacted to explain the number of offspring; buttercup had a positive effect only when the number of oaks was above the mean for the studied sectors. The results show that quality of complex and pasture‐rich landscapes for O. bicornis depends on preserving existing and generating new oak trees. Lignose plants are key early‐season forage resources in agricultural landscapes. Increasing habitat heterogeneity with trees and shrubs and promoting suitable late‐flowering forbs can benefit O. bicornis and other wild bees active in spring and early summer, something which existing agri‐environment schemes seldom target.