Zymomonas mobilis is a bacterium of industrial interest due to its high ethanol productivity and high tolerance to stresses. Although the physiological parameters of fermentation are well characterized, there are few studies on the molecular mechanisms that regulate the response to fermentative stress. Z. mobilis ZM4 presents five different sigma factors identified in the genome annotation, but the absence of sigma 38 leads to the questioning of which sigma factors are responsible for its mechanism of fermentative stress response. Thus, in this study, factors sigma 32 and sigma 24, traditionally related to heat shock, were tested for their influence on the response to osmotic and ethanol stress. The overexpression of these sigma factors in Z. mobilis ZM4 strain confirmed that both are associated with heat shock response, as described in other bacteria. Moreover, sigma 32 has also a role in the adaptation to osmotic stress, increasing both growth rate and glucose influx rate. The same strain that overexpresses sigma 32 also showed a decrease in ethanol tolerance, suggesting an antagonism between these two mechanisms. It was not possible to conclude if sigma 24 really affects ethanol tolerance in Z. mobilis, but the overexpression of this sigma factor led to a decrease in ethanol productivity.

Sugarcane bagasse is an agricultural residue rich in xylose, which may be used as a feedstock for the production of high-value-added chemicals, such as xylonic acid, an organic acid listed as one of the top 30 value-added chemicals on a NREL report. Here, Zymomonas mobilis was engineered for the first time to produce xylonic acid from sugarcane bagasse hydrolysate. Seven coding genes for xylose dehydrogenase (XDH) were tested. The expression of XDH gene from Paraburkholderia xenovorans allowed the highest production of xylonic acid (26.17 ± 0.58 g L−1) from 50 g L−1 xylose in shake flasks, with a productivity of 1.85 ± 0.06 g L−1 h−1 and a yield of 1.04 ± 0.04 gAX/gX. Deletion of the xylose reductase gene further increased the production of xylonic acid to 56.44 ± 1.93 g L−1 from 54.27 ± 0.26 g L−1 xylose in a bioreactor. Strain performance was also evaluated in sugarcane bagasse hydrolysate as a cheap feedstock, which resulted in the production of 11.13 g L−1 xylonic acid from 10 g L−1 xylose. The results show that Z. mobilis may be regarded as a potential platform for the production of organic acids from cheap lignocellulosic biomass in the context of biorefineries.

A contaminação de produtos avícolas por Salmonella tem sido um real desafio à avicultura desde o reconhecimento da carne de frango e ovos como importantes fontes de transmissão de salmonelas para humanos. O estado imune das aves tem um papel crítico na defesa contra diferentes patógenos. Lotes de aves com imunossupressão sofrem aumento da incidência de infecções secundárias e têm seu desempenho afetado negativamente. Entre os patógenos virais aviários que têm capacidade imunossupressora encontra-se o vírus da doença infecciosa da bursa ou doença de Gumboro. Neste estudo, avaliou-se a população linfocitária bursal através de exame histopatológico e a contagem de Salmonella em cecos de frango de corte através do método do número mais provável (NMP) buscando-se correlacionar estes fatores. Foram coletados os cecos e as bolsas de Fabricius (BF) de 347 frangos de corte com 28 dias de idade. Os cecos foram congelados e analisados pela microbiologia convencional para determinar a presença ou ausência de Salmonella sp e as amostras positivas submetidas à técnica de contagem pelo NMP. Foram identificadas duas amostras positivas (0,58%) para Salmonella Enteritidis e estas apresentaram 0 e 21 NMP/g, enquanto os cecos correspondentes apresentaram entre 60-70% de depleção linfocitária. Outros gêneros bacterianos identificados foram Providencia rettgeri, Proteus mirabilis e E. coli. Os escores histopatológicos evidenciaram depleção linfocitária moderada a severa nas bursas, porém o isolamento de Salmonella Enteritidis em duas amostras não possibilitou maiores inferências a respeito do envolvimento da Doença de Gumboro quanto à persistência de salmonelas no ceco das aves analisadas, sob a presente metodologia.