Ruminal Bacterial Community Composition in Dairy Cows Is Dynamic over the Course of Two Lactations and Correlates with Feed Efficiency.

Fourteen Holstein cows of similar ages were monitored through their first two lactation cycles, during which ruminal solids and liquids, milk samples, production data, and feed consumption data were collected for each cow during early (76 to 82 days in milk [DIM]), middle (151 to 157 DIM), and late (251 to 257 DIM) lactation periods. The bacterial community of each ruminal sample was determined by sequencing the region from V6 to V8 of the 16S rRNA gene using 454 pyrosequencing. Gross feed efficiency (GFE) for each cow was calculated by dividing her energy-corrected milk by dry matter intake (ECM/DMI) for each period of both lactation cycles. Four pairs of cows were identified that differed in milk production efficiency, as defined by residual feed intake (RFI), at the same level of ECM production. The most abundant phyla detected for all cows were Bacteroidetes (49.42%), Firmicutes (39.32%), Proteobacteria (5.67%), and Tenericutes (2.17%), and the most abundant genera included Prevotella (40.15%), Butyrivibrio (2.38%), Ruminococcus (2.35%), Coprococcus (2.29%), and Succiniclasticum (2.28%). The bacterial microbiota between the first and second lactation cycles were highly similar, but with a significant correlation between total community composition by ruminal phase and specific bacteria whose relative sequence abundances displayed significant positive or negative correlation with GFE or RFI. These data suggest that the ruminal bacterial community is dynamic in terms of membership and diversity and that specific members are associated with high and low milk production efficiency over two lactation cycles.

Serine/threonine phosphatase Stp1 mediates post-transcriptional regulation of hemolysin, autolysis, and virulence of group B Streptococcus.

Elucidating how serine/threonine phosphatases regulate kinase function and bacterial virulence is critical for our ability to combat these infections. Group B streptococci (GBS) are ß-hemolytic Gram-positive bacteria that cause invasive infections in humans. To adapt to environmental changes, GBS encodes signaling mechanisms comprising two component systems and eukaryotic-like enzymes. We have previously described the importance of the serine/threonine kinase Stk1 to GBS pathogenesis. However, how the presence or absence of the cognate serine/threonine phosphatase Stp1 affects Stk1 function and GBS virulence is not known. Here, we show that GBS deficient only in Stp1 expression are markedly reduced for their ability to cause systemic infections, exhibit decreased ß-hemolysin/cytolysin activity, and show increased sensitivity to autolysis. Although transcription of genes important for ß-hemolysin/cytolysin expression and export is similar to the wild type (WT), 294 genes (excluding stp1) showed altered expression in the stp1 mutant and included autolysin genes. Furthermore, phosphopeptide enrichment analysis identified that 35 serine/threonine phosphopeptides, corresponding to 27 proteins, were unique to the stp1 mutant. This included phosphorylation of ATP synthase, DNA and RNA helicases, and proteins important for cell division and protein synthesis. Collectively, our results indicate that Stp1 is important for appropriate regulation of Stk1 function, hemolysin activity, autolysis, and GBS virulence.

Regulation of CovR expression in Group B Streptococcus impacts blood-brain barrier penetration.

Group B Streptococcus (GBS) is an important cause of invasive infections in humans. The pathogen encodes a number of virulence factors including the pluripotent beta-haemolysin/cytolysin (beta-H/C). As GBS has the disposition of both a commensal organism and an invasive pathogen, it is important for the organism to appropriately regulate beta-H/C and other virulence factors in response to the environment. GBS can repress transcription of beta-H/C using the two-component system, CovR/CovS. Recently, we described that the serine/threonine kinase Stk1 can phosphorylate CovR at threonine 65 to relieve repression of beta-H/C. In this study, we show that infection with CovR-deficient GBS strains resulted in increased sepsis. Although CovR-deficient GBS showed decreased ability to invade the brain endothelium in vitro, they were more proficient in induction of permeability and pro-inflammatory signalling pathways in brain endothelium and penetration of the blood-brain barrier (BBB) in vivo. Microarray analysis revealed that CovR positively regulates its own expression and regulates the expression of 153 genes. Collectively, our results suggest that the positive feedback loop which regulates CovR transcription modulates host cell interaction and immune defence and may facilitate the transition of GBS from a commensal organism to a virulent meningeal pathogen.

Quorum sensing in bacterial species that use degenerate autoinducers can be tuned by using structurally identical non-native ligands.

Many bacteria use quorum sensing (QS) to regulate cell-density dependent phenotypes that play critical roles in the maintenance of their associations with eukaryotic hosts. In Gram-negative bacteria, QS is primarily controlled by N-acylated L-homoserine lactone (AHL) signals and their cognate LuxR-type receptors. AHL-LuxR-type receptor binding regulates the expression of target genes necessary for QS phenotypes. We recently identified a series of non-native AHLs capable of intercepting AHL-LuxR binding in the marine symbiont Vibrio fischeri, and thereby strongly promoting or inhibiting QS in this organism. V. fischeri utilizes N-(3-oxo)-hexanoyl L-HL (OHHL) as its primary QS signal, and OHHL is also used by several other bacterial species for QS. Such signal degeneracy is common among bacteria, and we sought to determine if our non-native LuxR agonists and antagonists, which are active in V. fischeri, would also modulate QS phenotypes in other bacteria that use OHHL. Herein, we report investigations into the activity of a set of synthetic LuxR modulators in the plant pathogen Pectobacterium carotovora subsp. carotovora Ecc71. This pathogen uses OHHL and two closely related LuxR-type receptors, ExpR1 and ExpR2, to control virulence, and we evaluated their responses to synthetic ligands by quantifying virulence factor production. Our results suggest an overall conservation in the activity trends of the ligands between the ExpR receptors in P. carotovora Ecc71 and LuxR in V. fischeri, and indicate that these compounds could be used as tools to study QS in an expanded set of bacteria. Notable differences in activity were apparent for certain compounds, however, and suggest that it might be possible to selectively regulate QS in bacteria that utilize degenerate AHLs.

Threonine phosphorylation prevents promoter DNA binding of the Group B Streptococcus response regulator CovR.

All living organisms communicate with the external environment for their survival and existence. In prokaryotes, communication is achieved by two-component systems (TCS) comprising histidine kinases and response regulators. In eukaryotes, signalling is accomplished by serine/threonine and tyrosine kinases. Although TCS and serine/threonine kinases coexist in prokaryotes, direct cross-talk between these families was first described in Group B Streptococcus (GBS). A serine/threonine kinase (Stk1) and a TCS (CovR/CovS) co-regulate toxin expression in GBS. Typically, promoter binding of regulators like CovR is controlled by phosphorylation of the conserved active site aspartate (D53). In this study, we show that Stk1 phosphorylates CovR at threonine 65. The functional consequence of threonine phosphorylation of CovR in GBS was evaluated using phosphomimetic and silencing substitutions. GBS encoding the phosphomimetic T65E allele are deficient for CovR regulation unlike strains encoding the non-phosphorylated T65A allele. Further, compared with wild-type or T65A CovR, the T65E CovR is unable to bind promoter DNA and is decreased for phosphorylation at D53, similar to Stk1-phosphorylated CovR. Collectively, we provide evidence for a novel mechanism of response regulator control that enables GBS (and possibly other prokaryotes) to fine-tune gene expression for environmental adaptation.

The ruminal bacterial community in lactating dairy cows has limited variation on a day-to-day basis.

Dairy cows rely on a complex ruminal microbiota to digest their host-indigestible feed. Our ability to characterize this microbiota has advanced significantly due to developments in next-generation sequencing. However, efforts to sample the rumen, which typically involves removing digesta directly from the rumen via a cannula, intubation, or rumenocentesis, is costly and labor intensive. As a result, the majority of studies characterizing the rumen microbiota are conducted on samples collected at a single time point. Currently, it is unknown whether there is significant day-to-day variation in the rumen microbiota, a factor that could strongly influence conclusion drawn from studies that sample at a single time point. To address this, we examined day-to-day changes in the ruminal microbiota of lactating dairy cows using next-generation sequencing to determine if single-day sampling is representative of sampling across 3 consecutive days. We sequenced single-day solid and liquid fractions of ruminal digesta collected over 3 consecutive days from 12 cannulated dairy cows during the early, middle, and late stages of a single lactation cycle using the V4 region of the bacterial 16S rRNA gene. We then generated 97% similarity operational taxonomic units (OTUs) from these sequences and showed that any of the individual samples from a given 3-day sampling period is equivalent to the mean OTUs determined from the combined 3-d data set. This finding was consistent for both solid and liquid fractions of the rumen, and we thus conclude that there is limited day-to-day variability in the rumen microbiota.

A phylogenetic analysis of the phylum Fibrobacteres.

Members of the phylum Fibrobacteres are highly efficient cellulolytic bacteria, best known for their role in rumen function and as potential sources of novel enzymes for bioenergy applications. Despite being key members of ruminants and other digestive microbial communities, our knowledge of this phylum remains incomplete, as much of our understanding is focused on two recognized species, Fibrobacter succinogenes and F. intestinalis. As a result, we lack insights regarding the environmental niche, host range, and phylogenetic organization of this phylum. Here, we analyzed over 1000 16S rRNA Fibrobacteres sequences available from public databases to establish a phylogenetic framework for this phylum. We identify both species- and genus-level clades that are suggestive of previously unknown taxonomic relationships between Fibrobacteres in addition to their putative lifestyles as host-associated or free-living. Our results shed light on this poorly understood phylum and will be useful for elucidating the function, distribution, and diversity of these bacteria in their niches.

The genome sequences of Cellulomonas fimi and "Cellvibrio gilvus" reveal the cellulolytic strategies of two facultative anaerobes, transfer of "Cellvibrio gilvus" to the genus Cellulomonas, and proposal of Cellulomonas gilvus sp. nov.

Actinobacteria in the genus Cellulomonas are the only known and reported cellulolytic facultative anaerobes. To better understand the cellulolytic strategy employed by these bacteria, we sequenced the genome of the Cellulomonas fimi ATCC 484(T). For comparative purposes, we also sequenced the genome of the aerobic cellulolytic "Cellvibrio gilvus" ATCC 13127(T). An initial analysis of these genomes using phylogenetic and whole-genome comparison revealed that "Cellvibrio gilvus" belongs to the genus Cellulomonas. We thus propose to assign "Cellvibrio gilvus" to the genus Cellulomonas. A comparative genomics analysis between these two Cellulomonas genome sequences and the recently completed genome for Cellulomonas flavigena ATCC 482(T) showed that these cellulomonads do not encode cellulosomes but appear to degrade cellulose by secreting multi-domain glycoside hydrolases. Despite the minimal number of carbohydrate-active enzymes encoded by these genomes, as compared to other known cellulolytic organisms, these bacteria were found to be proficient at degrading and utilizing a diverse set of carbohydrates, including crystalline cellulose. Moreover, they also encode for proteins required for the fermentation of hexose and xylose sugars into products such as ethanol. Finally, we found relatively few significant differences between the predicted carbohydrate-active enzymes encoded by these Cellulomonas genomes, in contrast to previous studies reporting differences in physiological approaches for carbohydrate degradation. Our sequencing and analysis of these genomes sheds light onto the mechanism through which these facultative anaerobes degrade cellulose, suggesting that the sequenced cellulomonads use secreted, multidomain enzymes to degrade cellulose in a way that is distinct from known anaerobic cellulolytic strategies.

Characterizing the microbiota across the gastrointestinal tract of a Brazilian Nelore steer.

The gastrointestinal tracts (GIT) of herbivores harbor dense and diverse microbiota that has beneficial interactions with the host, particularly for agriculturally relevant animals like ruminants such as cattle. When assessing ruminant health, microbiological indicators are often derived from the rumen or feces. However, it is probable that ruminal and fecal microbiota do not reflect the microbial communities within the GIT of ruminants. To test this, we investigated the compartments of the GIT from a Brazilian Nelore steer and performed a 16S rRNA pyrosequencing analysis on the collected samples. Our results showed high intra-individual variation, with samples clustering according to their location in the GIT including the forestomach, small intestine, and large intestine. Although sequences related to the phyla Firmicutes and Bacteroidetes predominated all samples, there was a remarkable variation at the family level. Comparisons between the microbiota in the rumen, feces, and other GIT components showed distinct differences in microbial community. This work is the first intensive non-culture based GIT microbiota analysis for any ruminant and provides a framework for understanding how host microbiota impact the health of bovines.

The entomopathogenic bacterial endosymbionts Xenorhabdus and Photorhabdus: convergent lifestyles from divergent genomes.

Members of the genus Xenorhabdus are entomopathogenic bacteria that associate with nematodes. The nematode-bacteria pair infects and kills insects, with both partners contributing to insect pathogenesis and the bacteria providing nutrition to the nematode from available insect-derived nutrients. The nematode provides the bacteria with protection from predators, access to nutrients, and a mechanism of dispersal. Members of the bacterial genus Photorhabdus also associate with nematodes to kill insects, and both genera of bacteria provide similar services to their different nematode hosts through unique physiological and metabolic mechanisms. We posited that these differences would be reflected in their respective genomes. To test this, we sequenced to completion the genomes of Xenorhabdus nematophila ATCC 19061 and Xenorhabdus bovienii SS-2004. As expected, both Xenorhabdus genomes encode many anti-insecticidal compounds, commensurate with their entomopathogenic lifestyle. Despite the similarities in lifestyle between Xenorhabdus and Photorhabdus bacteria, a comparative analysis of the Xenorhabdus, Photorhabdus luminescens, and P. asymbiotica genomes suggests genomic divergence. These findings indicate that evolutionary changes shaped by symbiotic interactions can follow different routes to achieve similar end points.

Identification of serine/threonine kinase substrates in the human pathogen group B streptococcus.

All living organisms respond to changes in their internal and external environment for their survival and existence. Signaling is primarily achieved through reversible phosphorylation of proteins in both prokaryotes and eukaryotes. A change in the phosphorylation state of a protein alters its function to enable the control of cellular responses. A number of serine/threonine kinases regulate the cellular responses of eukaryotes. Although common in eukaryotes, serine/threonine kinases have only recently been identified in prokaryotes. We have described that the human pathogen Group B Streptococcus (GBS, Streptococcus agalactiae) encodes a single membrane-associated, serine/threonine kinase (Stk1) that is important for virulence of this bacterium. In this study, we used a combination of phosphopeptide enrichment and mass spectrometry to enrich and identify serine (S) and threonine (T) phosphopeptides of GBS. A comparison of S/T phosphopeptides identified from the Stk1 expressing strains to the isogenic stk1 mutant indicates that 10 proteins are potential substrates of the GBS Stk1 enzyme. Some of these proteins are phosphorylated by Stk1 in vitro and a site-directed substitution of the phosphorylated threonine to an alanine abolished phosphorylation of an Stk1 substrate. Collectively, these studies provide a novel approach to identify serine/threonine kinase substrates for insight into their signaling in human pathogens like GBS.